by Trevor White
Over the years I’ve been a member of many sorts of club – some good, some … well less so. However, membership of an active motorcycle club such as the Classic Wing Club has always brought something special. No other membership is so willing to share its knowledge and experience so much. Indeed, people can be so ready to help that one can get a bit of a bad conscience. No! it’s not that I’m unwilling to share, but I have doubts about what I can share. When I think about it, I don’t really have that much knowledge about motorcycles. True, after so many years I do have some experience to pass on. Yet that is not experience about builds and re-builds, wrenching this or tweaking that. It is more an experience about riding. However, that experience is in my world, in my conditions – and that may be very different to yours.
An example of some experience and not much knowledge is my response to questions like, “After 24 years I have to replace the OEM tyres on my 1976 GL1000. What do you recommend?” I commonly answer by suggesting this is like asking how long a piece of rubber string is – and I mean it because, if the question can be answered at all, a whole wealth of additional information is required – none of it related to an understanding of tyre specifications. My style of riding varies from sedate swanning to serious scratching – the former anywhere the mood takes, the latter mostly in the nearby mountain environment. Then, we criss-cross the continent to attend weekend events, so 500-600 miles of highways – at cruising speeds of 85-90 mph – on Thursday/Friday and back three days later are not unusual. Then, maybe the biggest difference between you and I is me! I know what I want from my tyres. I want them to feel right – and that means ‘anonymity’. I just don’t want to know they are there, I don’t want them to intrude on my riding at all.
Obviously, mileage is an important aspect of tyres, but even that has to fitted into an overall framework. I just worked out a few prices. Let’s say I ride through a set of tyres in my 10’000 mile riding season. At current European prices and exchange rates, the season’s fuel costs me $0.036 per mile. The Michelin Macadam 50 tyres we run cost almost exactly $200 a set. Therefore, my rubber costs $0.020 per mile – about half the cost of gas (and don’t forget the expense of oil, etc., coffee and doughnuts to do those miles!) I would like to save, say, $50 with other tyres – but not if they don’t feel right. Yes, I would like to squeeze another 1000 miles of wear out of them but, if they stop feeling right without even reaching the 1.6 mm legal tread limit, they will get replaced. A thousand miles contains about 10% of the situations where I need maximal feel and traction – and trading that for $20 is no profit – for me! So, based on knowledge I can’t recommend any tyres to you. All I can do is to offer my experience about what questions you have to ask yourself.
SQUEEZE & BANG
The previous paragraph was an example of experience and personal taste that can be swapped. Yet, I mustn’t do myself down on all counts. There is some knowledge I can share – such as that about a bit of chemistry and combustion technology. Take the perennial subject of octane rating – as in, “Hey, you guys. I put in 98 octane fuel and the old girl took off like Starship Enterprise. Whad d’you use?” (Now, don’t let us get into a debate about U.S. and European octane designations. We will just assume that 98 is the highest rated – and highest priced – fuel at the pumps.)
Now, it’s time to share with you the knowledge of the High Mathematics of the Internal Combustion Engine that I have had since I was a nipper. It doesn’t originate with Einstein but it can be looked upon as The Unified Theory (TUT!). Avoiding complicated terminology it says:
Suck + Squeeze + Bang + Blow = Power (1)
Now, for the moment I will assume that sometime during 125 years engine builders managed to get the suck, and blow bit more or less right. They got the 14:1 air/fuel mixture worked out (that’s chemistry!). They could spark it right to release the energy locked up in the fuel (that’s a bit more chemistry!) and they can get the garbage out again. So, here we are just talking about the release of energy from a smooth flame moving through a combustible mixture – the squeeze and bang.
One of the first insights of engineers was to recognize that to squeeze the mixture into a smaller space – by increasing the Compression Ratio (CP) – would result in a more effective bang. Consider the moment when the fuel burns. This massively increases the volume of the gases in the combustion space but, at that moment, they are still contained within the combustion space. Consider the effect on the gases’ pressure if that combustion space is halved. For a fixed amount of gas there is a very simple relationship between its pressure (P) and volume (V) in situation Aand situation B, which goes like:
Pressure A x Volume A = Pressure B x Volume B (2)
By jiggling around with the units and dividing by the current price of cabbages, this simplifies down to something even I can understand, to whit:
Squeeze BIG = Bang BIG (3)
So, if Volume A of the expanding gases in the low-compression engine is halved by reducing the combustion space in which it is released, then its pressure must double. It is this increased pressure that, initially, is more effective in driving down the piston. The engineers were not getting more energy out of the fuel. They were making that energy work more effectively. In the first instance it was nothing at all to do with the fuel. It was the use of the physics of gas volumes and pressures.
Still, it looks good, doesn’t it? That’s what those early engineers thought – and so they started happily increasing compression ratios. However, with the then available fuels they soon ran into a secondary problem. Their high compression engines started sounding like a bag of old nails, wore out very quickly and did not produce the expected power increases. They soon found that the highly compressed mixtures were no longer burning evenly. The flame front was progressing very raggedly across the combustion space, through local pressure waves causing the piston to shake and judder down instead of being smoothly whooshed down. Not only that, but the compression process generates heat itself. The compression process itself could cause spontaneous ignition as in a diesel motor. With more engine heat and any hot spots caused by engine deposits in the combustion space or on the valves, the mixture could also ignite before it should, before the piston and valves were at the right point for maximally effective combustion. This led to all those nasty symptoms that we now call ‘pinking’ in English, ‘pinging’ in American and ‘klopfen’ (knocking) in German. And the worst symptom of all was a loss of effective power – even before the engine fell apart from stress.
So, the boffins had to find a cheap and efficient way to make highly compressed mixtures that did not pre-ignite or burn unevenly. This they did in the late 1920s. The problem was solved by adding a few parts-per-million (a handful of molecules) of lead tetra-ethyl to the fuel. They also had to find a scale for categorizing the properties of these fuels. This is where the Octane Rating came in. The engineers established a standard engine and tested fuels for their ability to resist knocking. The reference fuel was a mixture of two hydrocarbons – iso-octane that resists knocking and heptane that readily knocks. The Octane Number of a fuel was based on the % mixture of these two that matched the test fuel in anti-knock properties. (Of course the matter is confused with two measuring procedures that give Research Octane (RON) or Motor Octane (MON) Numbers – and the tendency for the US to use an average of these two!)
Engines are obviously designed for a particular fuel. By modern standards, Gold Wings are relatively low in compression (9.2:1). Indeed, Honda recommends non-leaded 92 RON in Europe. (They didn’t need an unforeseen advantage that leaded fuel brought with it. Lead could leave a micro-layer on the valve seats. This acted as a protective cushion against the pounding valves – so allowing cheap-skate manufacturers to save money by having the valves set into cast iron seats. Those with aluminium heads, like Honda, obviously needed inset hardened seats from the outset – and these didn’t need that cushion.) The lowest octane grade available here is unleaded 95 RON, when we could use 92 to prevent power loss through knocking. We do not gain any power with 95. We would not gain any power with 98. We would simply lose money. With a properly tuned ignition system there is no energy in a few molecules of lead. If, without re-designing the carburation, camshaft and/or the exhaust (what else is there?), a claim that putting in high-octane gasoline improves a bike’s performance could be substantiated, then I suggest that we are talking about a very sick engine. It could better profit from having a copper pendulum swinging over it or one of Pharaoh’s shinbones in the tool-tray! Octane ratings are to do with potential losses of power, not gains.
Trying to illuminate the shadows of my ignorance in other areas, I occasionally succeed in bringing a little light on the matter – at other times I only throw my ignorance into high relief! For instance, I became aware that I tended to believe an implicit old wife’s tale. I had grown up in a pretty feline world of motorcycles. There was the long-stroke Panther single and the Triumph Tiger twins. The Panther was regarded as a ‘thumper’ – a torque machine best at hauling family sidecars in pre-Mini days. The Triumphs were looked upon as spitting and scratching horsepower demons. So, implanted in my mind was the idea that torque and horsepower were two different animals – and you couldn’t have both animals at once.
Then, I recall my very first clear memory of a motorcycle – when I was about nine or ten. One of the neighbourhood lads owned it – a beautiful leaf-green and gold pre-war, two-stroke Scott, with burnished brass fittings. (Was that the birth of my interest in motorcycles Gold in name and colour?) I acquired street cred and stature just by hanging on to the fringes of the gang kicking tyres about this and other machines. Obviously I was well brought up enough not to mix in with the conversation of these important men, my elders, but that gave me all the more time to let my eyes linger over that machine. With that serpentine colour and slinky shape, it just had to handle well. Unfortunately that expectation was not met – for soon after the lad ran out of road at a large urban roundabout, and buried his unhelmeted head terminally in an ill-placed tree.
Then there were the ubiquitous British twins. Is that when I first learned the power enhancing effect of accessories, such as the twin carbs on the SS Super-Sports versions, with their seductive bell-mouths sucking in imaginary power from the air. Perhaps these were the origin of so-called Mark I tunings. These appeared mostly on cars. Glue a strip of chequered sticker tape on the side, add the letters ‘GT’, and the car was sure to go 5 mph faster! Certainly the gaping shark jaws I, as an 18 year-old, painted on the Avon fairing of my 350 cc AJS added to its predatory power. I was convinced that this predatory power helped me eat my way through city traffic.
Could it be that these well-informed ignorances still affected my attitudes to the early Wings? I mean, they were tourers, weren’t they. Tourers don’t have gut-wrenching horsepower to hurtle themselves and their riders up to warp speeds. No. Honda had made the choice for torque – and that excluded horsepower … didn’t it? Recently, realizing that I didn’t have many answers – mainly because I knew even fewer questions, I decided to leave the safe plateau of ignorance and start down the slippery path into the eternally deep pit of knowledge.
However, I seldom need one good reason for doing anything that stresses my brain-box – I need several! A second reason came along when I realised that keeping classic bikes on the road was becoming more and more difficult. Basic originality was becoming increasingly difficult to sustain because of the unavailability of parts or the funds to pay for the few remaining. There are constant discussions about the wish or desire to replace parts with non-original (non-OEM) parts. This is not so problematic with cycle parts, but what happens with non-OEM engine parts? Here, most discussion centres on carburettors and exhausts. Now, in my TUT mentioned above, these are in the Suck and Blow part of the equation and so could affect Power. I wanted to know how. I wanted to be able to judge what non-OEM parts could affect the performance of my old Wing – for good or bad.
I had the good fortune to stumble across aids to my scholarship – ones that offered the possibility not necessarily of knowing a few more answers but of being puzzled by a few more questions. These were the publications of the Californian-based Motion Software (www.motionsoftware.com). The basis product is a PC-based engine simulation software, Dyna2000, now in version 3.08. Coupled with this are Larry Atherton’s various handbooks that not only guide the user but explain the technical background to engines and their simulation, in very easy-to-read text (down-loadable from the website, as PDF files). Importantly, they blew away many of the pre-conceptions that I had carried around with me for decades. Additionally to this, I excavated one of the shoeboxes under my bed to come up with a few of useful cornflake packet cut-outs, such as:
J. Bradley, The Racing Motorcycle: A Technical Guide for Construction. 405 pp., Broadland Leisure Publications, York, UK, 1996.
G. Cocco, Motorcycle Design and Technology. 215 pp., Vimodrone, Italy, Giorgio Nada Editore, 1999.
P.E. Irving, Motorcycle Engineering. 326 pp., Los Angeles, CA, Clymer Publications, 1973.
P.E. Irving, Motorcycle Technicalities. 97 pp, Sydney, Turton & Armstrong, 1973. (Articles by “Slide Rule“, Motorcycling, 1932-1944)
P.E. Irvine, Tuning for Speed: How to Increase the Performance of Motorcycle Engines for Touring, Racing and Competition Work. 6th edn., 260 pp., Sydney, Australia, Turton & Armstrong, 1987.
J. Robinson, Motorcycle Tuning: Four-Stroke. 2nd edn., 178 pp., Oxford, UK, Newnes, 1994.
P.H. Smith & J.C. Morrison, Scientific Design of Exhaust & Intake Systems. 3rd edn., 274 pp., Robert Bentley, Cambridge, MA, 1971.
J. Stoffregen, Motorradtechnik: Grundlagen und Konzepte von Motor, Antrieb und Fahrwerk. 322 pp, Vieweg, Wiesbaden, FRG, 1995. (In German)
Oh! Yes. There was a third reason for pursing this knowledge. I wanted to upstage you lads and lasses. I was also a young lad when I discovered a very effective alternative to knowledge – confidence! Let me take a current situation to illustrate this. I would be King, a highly respected king in all the bar-rooms of Miami or Palm Beach these days. I would stay quiet while the arguments – and maybe the bottles – went to and fro. At an opportune moment, when words failed the others or the blood had to be staunched I would, for example, firmly say something like: “I think the solution can be found in Bumsrusher vs. The State of Florida, 1892 … mmm … November, I think.“
This is, of course, total nonsense. However, uttered with the confidence of papal infallibility, few will question it. (That is a Power of a non-mechanical sort!) If some delicate soul does admit to a lack of conviction, like “O.K., smartass, wotsthat gotta do wiv it?“, and backs up his query with a fist the size of a football, then you may have to reveal a few more details of the case. “Well, as anyone knows, it was concerned with the legality of building a privy behind a cat-house – someone’s right to dig a hole and for someone else to fill it with sh… oops! … manure while everyone up at the house is screwing themselves or each other. I think an intelligent person like you can only get the flavour of the case by reading the original.“
So, as you see, there were many reasons for laying aside my favourite hobby – laziness – and getting the gray cells into gear. One of the first things I learned (better late than never) was that the internal combustion engine is nothing more than a self-driven gas pump. You could test this by disconnecting the ignition and connecting up an electric motor to the crankshaft. By spinning the crankshaft you would pump air from outside into the intake tract, through the pots and out of the exhaust. This is a pretty useless exercise pumping atmospheric air into the atmosphere because all that this pumping does is to consume power – giving a pumping loss. However, what if, in the middle of this pumping action, you gave the system a judiciously placed bang in the butt? You may not only overcome those pumping losses, but you may be able to connect the system up to itself – to eliminate that electric starter motor that got the thing turning in the first place. You may also end up with some excess power that, with the addition of a couple of wheels could drive that engine down the street and into the mountains. Now, it was when that slippery path led me to this point that I began to get interested. I thought I could be on the verge of inventing something. (I would call it a motorcycle.) But I still didn’t really know the difference between horsepower and torque. So, back to the armchair.
I recalled Mr. Davies, our second-year physics master at the local Grammar School nearly 50 years ago. (He was affectionately known as “Tosser”, due to his habit of playing ‘pocket billiards’ in front of the class. But that’s not why I remembered him at this juncture.) No, Tosser introduced us to engines – as known to physics. It seems that an engine is a device for doing work, usually by the conversion of one sort of energy into another. Clearly, the internal combustion engine does this, releasing chemical energy to apply a force to a wheel at the back of some mechanical contraption. If this force is strong enough to move the weight of the vehicle, then the engineers say that work is done – and they can measure that. The units they use for this measure – foot-pounds (ft.lbs) – give a clue to what is being measured. If the force moves one pound of weight a distance of one foot, then one foot-pound of work is done. However, if that movement is in a circular direction, as with most engines, then a new name had to be found for that capacity for doing work – and that was torque.
(Don’t think for a moment that ‘work’ is a man-made process, arising from his machines. You stumble across Nature ‘working’ all the time. Think of that Pacific tectonic plate shoving against the American West Coast. It may only move millimetres per year, but those forces move billions of tons of good ol’ USA sideways and a few Rocky Mountains into the sky. Now, that is work, however slowly accomplished.)
THE POWER OF HORSES
However, humans being what they are, they are not just interested in whether a thing happens or not – they must know how quickly it happens. With engines they wanted to know the rate at which the work was done. The 18th century Scottish engineer, Jimmy Watt, came up with a suggestion. He reckoned that a horse could pull 200 pounds over 110 feet (22’000 ft.lbs) in a minute. Therefore, he assumed that any engine that could do this had the power of one horse. Later, he must have gone over the border to test English horses, because he adjusted the power of a horse to 300 lbs over 110 feet. That measure of horsepower (HP), 33’000 ft.lbs per minute or 550 ft.lbs/sec is still used today – except by us funny Europeans who want to use more logical metric units. No sense of tradition, us lot!
So, horsepower is only the rate at which work is done – and is directly related to it by a time factor. It is no different for torque though, because the forces are circular, the factor of pi comes into the equation as well as the rate at which the circular motion takes place. This, of course, the number of revolutions per minute, the RPM. So, by jiggling the numbers, the conversion to horsepower can be made with:
HP = Torque (ft.lbs) x RPM/5252 ft.lbs/min (4)
Although HP is directly related to torque, the relationship is not linear. This is due to that RPM/5252 multiplication factor. It changes as you move over the RPM range. To show this, imagine an engine producing the following torque band, in ft.lbs at various rpm:
75.0 @ 4500, 80.0 @ 5000, 75.0 @ 5500, 70.0 @ 6000, 65.0 @ 6500, 60.0 @ 7000
With the torque peaking at 5000 rpm, my trusty Texas TI-58 calculator (also a late 1970s classic) gives the following power curve, in HP @ rpm:
64.3 @ 4500, 76.0 @ 5000, 78.5 @ 5550, 80.0 @ 6000, 80.4 @ 6500, 80.0 @ 7000
The HP peaks at 6500 rpm. Now, assume we want to have more torque around at lower engine speeds, say, for sidecar pulling. We tweak the engine differently, so that it produces the same torque curve, but shifted 500 rpm lower down the rev-band so that the 80 ft.lbs peak at 4500 rpm. The HP power curve would then look like:
68.5 @ 4500, 71.4 @ 5000, 73.3 @ 5500, 74.3 @ 6000, 74.3 @ 6500, 73.3 @ 7000
Now, I am beginning to get the first insights into engine manipulation. All we have just done is to change the engine speed at which it delivers the same amount of torque to the crankshaft, and we have markedly changed the HP-curve. Gaining low-down torque has resulted in a ‘loss’ of about 6 HP at its peak. That same amount of work, but at lower rates – or rpm – results in the rated HP being less and tending to come down the rev-band. Obviously, doing the reverse – sacrificing the low-down torque by pushing that peak 500 rpm up the rev-band to 5500 rpm – does result in more peak power (86.6 HP @ 6500). However, the cost would be less tractability at those lower rpm.
So, there are no free lunches. HP or torque can be gained or lost up and down the rev-band. The simple conclusion would seem just to be a matter of choice. Unfortunately life isn’t that simple. The engine may be tweaked to get more of this or that, but the bike may not be able to use the extra something. When the basic power curves were obtained, a smart manufacturer would design the gearbox to make optimal use of that power over the rev-band. A tweak to produce a new power curve may not suit that OEM gearing. Technically it is not so difficult to get a bit more torque or horsepower here or there from a standard, suit-all-tastes engine. Tweaking the gearing, however, is a major (a.k.a. expensive) undertaking.
My intense researches have now reached the point where I want to know what sort of tweaks or manipulations can shift the power curves around. That meant that I needed the starting info on the specifications of the four-cylinder Wings (are there any others?). So, it was back under the bed, to search through the workshop manuals hiding in that shoebox. For the Wings of interest (to me), I assembled the available data in Table 1 following. Before we get on to that, though, we have to think about Old Nick who conceived of the four-stroke internal combustion engine. That does not mean that I am a hairshirt-wearing tree-hugger who sees the Devil in all things mechanical. I am talking about Nicolas Otto. Although he made the crucial breakthrough in design in 1876, with the 4-stroke cycle providing that all important compression stroke, he didn’t see far enough into the Suck and Blow bit of power-making.
To be fair, perhaps the dynamic behaviour of gases was not well understood then, nor wave dynamics mathematics, nor even something as simple as organ pipes. Nick seemed to have seen the Sucking and Blowing to take place with static lumps of gas, and not entities that changed their properties when moving and changed them again when moving at high speeds. Well, his engine itself was no turbo, turning over at about 160 rpm. So, his Suck and Blow were timed maybe just as I would have timed them. Otto’s intake valve opened just when the piston was at its top dead centre (TDC) point, so that the immediately descending piston pulled in the fresh charge. It was closed at the piston’s bottom dead centre (BDC) point, so that when it ascended, it could compress the induced charge. When it reached TDC for the second time, at the point of maximal compression, the mixture was ignited so that the expanding combustion gases could push the piston back down again to the second BDC. It was then time to get rid of the spent gases, so the exhaust valve was opened at BDC so that the then ascending piston could drive then out and be ready for the next four strokes to begin. Seems neat and logical, doesn’t it? No trade-offs. However, now we have to start looking at those other properties of moving gases, to see whether any trade can actually increase power. Let’s start back to front, looking at that exhaust, Blow stage.
Clearly, the efficiency of the engine depends on removing those spent gases, to make way for fresh charge. If the exhaust valve doesn’t open early enough to give time for them to get out, power will go down. But what is early enough? At first sight, opening the exhaust valve before BDC (BBDC) should cause a loss of piston-pushing power from the combustion stroke because the excess pressure goes down the spout. However, releasing the exhaust gases at high pressure allows them to get up speed, swoosh down the pipes and then, further encouraged by the rising piston, get out of the way for fresh charge. This leads to power gains. So, the trick is to get a positive balance from the loss of power due to early exhaust opening and the power gains this brings. It was found that exhaust valve opening some considerable time before BBDC does give this positive balance. But when do you close the exhaust? For that we have to get into wave dynamics – about which I know nothing!
My recent reading showed that I was 60 years out of date. I still entertained a concept that was disproved decades ago. I always thought that cylinder emptying was helped by the momentum of the slug of exhaust gases. Rushing down the pipes it sort of ‘sucked’ the residual gases out with it, on its shirt tails. That ain’t so! Of course, contained within the pipe, the gases flow down the pipe with a positive wave of high pressure. However, a peculiar thing happens when they pop out of the pipe. Wave-dynamic processes cause a wave of negative pressure to flow back up the pipe at supersonic speeds. This does not necessarily affect the movement of gas particles still flowing out. (This might be understood by considering a smooth-surfaced flowing stream. Going with the flow is a cork. Tossing a stone ahead of the cork causes the characteristic ripples to spread out. These also spread upstream. They cause the cork to bob up and down, but they do not impede its flow downstream.).
Now, if the exhaust valve is still open when that negative pulse arrives back at the cylinder, it is this that pulls out more exhaust gases, scavenges them. So, the longer the exhaust valve stays open, the more chance this effect has of working. Nonetheless, the timing has got to be just right. The speed of these dynamic waves is pretty constant. However, the times when the exhaust valve is open depend on the engine rpm. Therefore, this exhaust-induced increase in power may operate only over a limited range of rpm.
A further point to consider is that the time the gases need to pop out of the exhaust-pipe and for the returning pulse to arrive back at the cylinder obviously depends on the length of the exhaust system. Still further, the nature of the exhaust ending (or the pseudo-ending created by a voluminous expansion box) can also have an effect. Fitting an open pipe that suddenly exits into the atmosphere produces a really definite, powerful pulse that returns up the pipe. This would have strong and definite scavenging effect – over a very narrow rpm range. With these powerful positive and negative pulses resonating up and down the pipe, we would also have a rather impressive trumpet effect – somewhat ear-shattering perhaps. If the exhaust header pipes reach the outside through a series of stepped pipes of increasing diameter – and maybe through a large collector box, then that one single pulse will be broken down into a series of lesser pulses spread out over time. Therefore, any scavenging will be less pronounced but available over a wider rpm-range.
Can this scavenging wave in the exhaust be used to any other advantage? It surely can. If the intake valve happens to be open when it arrives through an open exhaust valve, the negative pulse can also help to draw in fresh charge, filling the upper spaces and driving even more waste out. This occurs when the exhaust valve closes after the intake valve opens – giving an overlap when both valves are open. However, leave that exhaust valve open too long and, yes, power will go up because the scavenging is maximal. On the other hand, there is the danger that fresh charge also goes down the exhaust pipe – wasting fuel (which is also power) and worsening the emissions profile with unburned hydrocarbons. Therefore, the exhaust valve closing time has to be just right as well.
Of course, with the design of the exhaust system these factors can be tuned for a particular effect – to obtain something positive or avoid something negative. A non-OEM exhaust system could enhance a positive effect. It could destroy it. It might introduce a negative effect. It could produce more noise – and be illegal in some parts of the world. (Again addressing one of the old saws about vehicle noise – Loud Pipes Save Lives – any believer in this clap-trap should read Patrick J. Hahn’s recent article Loud and Clear in the electronic magazine The Interactive Motorcyclist (www.activebike.com).
If you remember, old Nick Otto had his intake valve open just at the moment when the piston was poised to descend on the induction stroke. What he didn’t know, however, was that he lost some of the induction efficiency this way. The valve isn’t closed one moment and open the next, hey presto! Controlled by the ramps of the cam, it has to be lifted off its seat and accelerated up to its maximum lifting speed. It then slows down to a stop when that maximum is reached, where its motion turns around. It then re-accelerates up to its maximum closing speed and then slows to settle into its seat again. Therefore, there is more efficient induction when the valve is already pretty well open as the piston starts pulling the mixture in. Additionally, to get the best suck from the descending piston, it would be advantageous when the valve is at maximal lift when the suck is maximal. That is just before the mid-point down, at about 70-80° after TDC (ATDC). So, for either profit, the valve best starts opening before TDC (BTDC). How much before also depends on that scavenging process mentioned. We have already decided to keep the exhaust valve open, overlapping with the open intake valve to produce the scavenging of residual exhaust gases and to start drawing in fresh charge before the piston actually starts to descend. It can’t open too early or else the piston ascending on the exhaust stroke would push the waste gases down the intake tract. This too has to be timed just right.
An additional element is the mixture itself. Even though it is gaseous, it can’t just gallop into the cylinder the moment the stable door opens. It has its inertia to overcome before its flow gets into its stride. That is another reason for having the valve open in plenty of time for scavenging waves to start the flow moving and for the descending piston then to take over. But once it is flowing, the properties of that mixture can change. At high flow rates it starts ‘thickening up’, whose momentum is difficult to stop. But who would want to stop fresh charge from getting into the cylinder? The more the merrier for extra power! So, although Otto closed the intake valve when the piston reached BDC, leaving it open longer allows aramming effect that gets more charge into the cylinder than just that drawn in by the swept volume of the piston. Again the timing for closing the intake valve has to be just right. Past BDC the piston has started to rise and compress the mixture. If this rising compression pressure exceeded the ramming pressure before the valve closed, charge would be pushed back down the intake tract. So, it closes after BDC (ABDC), but not too long after.
A rough estimate of this ramming effect can be calculated. From the engine specifications – tabulated in Table 1 – one can see that the swept volume of each cylinder is 60.96/4 = 15.24 cu.in (249.8 cc), combustion space of the GL1000s is 1.86 cu.in.(30.49 cc) and the combustion pressure is 171 psi (12.03 kg.cm2) The compressed charge of mixture started life at atmospheric pressure (14.7 psi, 1.0332 kg.cm2). We know from the formula (1) above that Pressure A x Volume A = Pressure B x Volume B, so an estimate of the charge volume before it got rammed into the cylinder is given by:
Induced Volume = [(171 x 1.86/14.7) – 1.86] = 19.78 cu.in (324.1 cc) (5)
If the induction had been left just to the piston moving down the cylinder, we couldn’t have got more than 15.24 cu.in (249.8 cc), the swept volume, into the pot.
Clearly, too, this ramming effect is greater if the induction flow velocity is increased. In order to get into the intake manifold, the induced volume of air has to pass through the venturi of the carburettor. If that venturi is made slightly smaller, then for the same volume of air to pass through the smaller diameter it has to move faster. This apparently does lead to better cylinder filling through ramming – and that improves the torque produced by the engine. However, there are obviously limits to this. Make it too small and the restriction may increase the speed of flow, but there is not enough time to pull in enough air – and the engine is starved of mixture. Again obvious is the fact that the changed air-flow speed also changes the low pressure that draws the fuel in through the jets. Therefore, there has to be a different jetting.
It seems that you can also change the engine performance by doing the opposite – opening up the venturi. The larger venturi slows down the air-flow speed but offers little restriction for the mixture to be sucked in rather than being rammed in. This is apparently relevant for getting peak horsepower when the engine has a wide open throttle (WOT) at high rpm. Because of the very brief valve-opening times, the availability of unrestricted mixture is more important than its speed. The problem of this system is at low engine speeds. The low velocity of the air passing through the venturi makes it difficult for the carburettor to get the mixture right and stable. Therefore, high WOT horsepower may be obtained but low speed response may be ragged.
Then there is the question of whether there are any resonant waves in the intake tract as there are in the exhaust. Well, yes, there are – except that the dynamic situation is a bit different – and very complicated! The exhaust tract has high-pressure gases passing from the valve to the atmosphere. The intake tract uses low pressure to draw mixture in from the atmosphere to the valve. Consider the engine running, and the mixture is flowing well through the intake valve into the cylinder. The intake then closes. The pressure waves generated bounce off this closed valve and run back along the intake tract. They pop off the open inlet end of the intake tract, create a reversed pressure wave that then runs back towards the valve. This resonance continues with a series of decaying amplitude pulses in the closed off system. This is just what happens in an organ-pipe. If the dimensions of the intake tract are well designed, this can have a very positive effect on cylinder filling when the intake valve does open. Again the frequency of this resonance influences the point in the rpm-range that peak power is obtained.
You may have seen set-ups that offer flexibility in this tuning. As the roving camera moves around the pits at motor races, you sometimes catch sight of some magnificent 8 or 12 cylinder engine. Most prominent is the battery of carburettors, with their highly polished trumpets standing out – indeed just like the pipes of some baroque organ. A wonderful sight! These bell-mouths may be 10-12 in. long – but they can be exchanged for others of different length. This would be done to modify the intake resonance, and with that the power band, to suit that particular track. So, I learn that changing the overall dimensions and design of intake systems can dramatically change the pattern of power just as – and maybe more than – exhaust changes.
Matters get complicated when the intake valve opens. The organ-pipe tuning breaks down and is replaced with so-called Helmholtz resonance. The mixture coming through the narrow intake port into the ‘big’ volume of the cylinder also starts resonating. (Larry Atherton likens this to the result of blowing into a whisky jug. There, the resonance process creates that deep sound that is sometimes used to provide the rhythm for a Southern States music band.) Harnessing this effect properly in an engine intake system can also bring dramatic improvements in cylinder-filling and performance – adding power, throttle response and fuel economy.
By the way, can you believe that until recently I went through Life knowing that it is important to keep the tappets – the valve clearances – well adjusted, but without knowing why? Alright, I always thought the clearances were there to take up heat expansion. Make the gap too small and at best the valve train is over-stressed, at worst a valve-stem is bent; make it too wide and the engine sounds like a cement-mixer as the valve and cam-follower wears excessively. But the recommended gap is specific, so that the cam-timing is correct in the warm engine. If the cam-follower has too little or too much distance to cover, then the valve operation is screwed up. Is there hope for me?
WHAT’S IN A WING?
As you can imagine, when I got this far, I didn’t want to see another dish of cornflakes in my life. I didn’t want to see another cornflake packet in the house, even though it meant I couldn’t complete my collection of plastic dinosaurs. However, what I did want to see was how these various design elements related to the specifications of the four-cylinder Gold Wings. I therefore collected up all the specs (of models of interest to me) in Table 1.
I didn’t get very far with my comparisons before another one of my preconceptions was shattered. It has been often said and written – and I have done that, too – that Honda didn’t really know what they were aiming for with the first GL1000. It was further said that the first American owners told them what they had produced – a tourer of the superlatives. Yet the specs seem to say that Honda did indeed know what it was doing. Look at those ’75/77 specs – the 32 mm carburettor, the valve lift of way less than 24-28% of the valve diameter, the cam timing, particularly with that very short intake-exhaust overlap of only 10°. All these specs are saying, “Conservative … conservative” … with a big C!
Honda did not give this engine any sporting pretensions at all. It is all laid out to give modest, unstressed performance – of a tourer – from Day 1. That didn’t change over the development years. The first changes occurred with the ’78 model – not to make the Wing a rice-rocket but to make it slightly more conservative. The cam timing is more conservative and the carburettor goes down to 31 mm. The resulting slight improvements in performance were in low-down torque rather than horsepower. Obviously, upping the capacity to the GL1100 and then the GL1200 couldn’t avoid increasing the horsepower, even though the carburettors were now down to 30 mm. The jump to 1085 cc, for instance, was an 8.6% increase in capacity. It brought a 6% increase in horsepower, but a 10% jump in torque.
Taking a different tack for a moment, engine specification and performance were not the only factors to change during Wing development. Weight changed as well. From the ‘75/77 to ‘78/79 GL1000, power didn’t change much, but weight went up by 9 kg (20 lb). Both of them, however, were still superior to the all-singing, all-dancing ’87 1200 Aspencade. Notably, the GL1100 provides both the best and the worst power:weight ratios of all 4-cylinder Gold Wings. The naked GL1100 carries the least fat per pound. Saddling it with the full fairing and luggage gave this Interstate Wing more pounds per power than any others.
In spite of this picture seeming reasonably clear to me, I still wanted some back-up evidence. So I raided my shoebox archive again, looking for the specs of bikes that were around at the time the Gold Wing was being designed. I couldn’t find full data, as Table 2 shows, but enough to make a comparison. To many, the ultimate sports tourer of the day was the BMW 90S. (I have long lusted after one!) At first sight, this boxer twin has a similarly conservative layout to the boxer-four Gold Wing – at least in respect to cam timing. However, look at that carburettor – compared with the Wing, its 38 mm Dell’Ortos are cavernous. And the valve heads – they’re the size of dinner plates. It may only produce 67 HP, but with 132 lbs less weight to carry, it left the Wing for dead in the power/weight ratio stakes.
GOLD WING ENGINE SPECIFICATIONS (4-cyl.)
Bore (B mm / in)
72.0 / 2.835
72.0 / 2.835
75.0 / 2.953
75.0 / 2.953
75.5 / 2.972
75.5 / 2.972
Stroke (S mm / in)
61.4 / 2.417
61.4 / 2.417
61.4 / 2417
61.4 / 2.217
66.0 / 2.598
66.0 / 2.598
Cubic capacity (CC cc / in3)
999 / 60.96
999 / 60.96
1085 / 66.21
1085 / 66.21
1181 / 72.07
1181 / 72.07
Compression ratio (CR)
Compression pressure (CP kg.cm-2 / psi)
12.03 / 171
12.03 / 171
12.03 / 171
12.03 / 171
13.01 / 185
13.01 / 185
Combustion Space (CV cc / in3)
30.49 / 1.860
30.49 / 1.860
33.08 / 2.019
33.08 / 2.019
36.94 / 2.254
36.94 / 2.254
Cam lobe base circle (CBC mm / in)
30.00 / 1.181
Cam lobe height intake (ICH mm / in)
37.14 / 1.462
36.80 / 1.449
37.00 / 1.457
37.00 / 1.457
35.80 / 1.409
35.57 / 1.400
exhaust (ECH mm / in)
36.80 / 1.449
36.80 / 1.449
36.80 / 1.449
36.80 / 1.449
35.80 / 1.400
Rocker arm ratio (RAR)
Valve lift intake (IVL mm / in)
8 50 / 0.335
8.50 / 0.335
8.80 / 0.346
8.80 / 0.346
9.00 / 0.354
9.00 / 0.354
exhaust (EVL mm / in)
8.50 / 0.335
8.50 / 0.335
8.50 / 0.335
8.50 / 0.335
9.00 / 0.354
9.00 / 0.354
Valve diameter intake (IVD mm / in)
38.0 / 1.496
38.0 / 1.496
38.0 / 1.496
38.0 / 1.496
36.0 / 1.417
36.0 / 1.417
exhaust (EVD mm / in)
32.0 / 1.260
32.0 / 1.260
32.0 / 1.260
32.0 / 1.260
32.0 / 1.260
32.0 / 1.260
Valve timing @ 1 mm / 0.04 in lift
Intake open (IVO ° BTDC)
close (IVC ° ABDC)
Exhaust open (EVO ° BBDC)
close (EVC ° ATDC)
Intake duration angle (IDA °)
cam angle (ICA °)
Exhaust duration angle (EDA °)
cam angle (ECA °)
Intake / Exhaust overlap (IEO °)
Carburetor venturi (CVD mm / in)
32 / 1.26
31 / 1.22
30 / 1.18
30 / 1.18
30 / 1.18
30 / 1.18
Dry Wt. (add ca. 23kg / 50lbs wet) (kg / lbs)
265 / 584
274 / 604
267 / 589
308 / 679
337 / 743
337 / 743
Published performance PS / HP
81 / 80 @ 7500
79 / 78 @ 7000
84 / 83 @ 7500
84 / 83 @ 7500
95 / 94 @ 7000
Torque(Nm / ftlbs)
80 / 59 @ 6500
83 / 61 @ 5500
91 / 67 @ 5500
91 / 67 @ 5500
105 / 77 @ 5000
Published Weight / Power Ratio (kg.PS-1 / lbs.HP-1)
3.27 / 7.30
3.47 / 7.74
3.26 / 7.18
3.76 / 8.28
3.55 / 7.90
|Bore (B mm / in)||90.0 / 3.54||61.0 / 2.40||73.0 /2.87|
|Stroke (S mm / in)||70.6 / 2.78||63.0 / 2.48||89.0 / 3.50|
|Cubic capacity (CC cc / in3)||898 /54.80||736/44.93||745 / 45.5|
|Compression ratio (CR)||9.5||9.0||8.9|
|Valve diameter intake (IVD mm / in)||42.0 / 1.65||?||38.0 / 1.50|
|exhaust (EVD mm / in)||40.0 / 1.57||?||33.0 / 1.30|
|Valve timing @ 1 mm / 0.04 in lift|
|Intake open (IVO ° BTDC)||10||5||50|
|close (IVC ° ABDC)||50||30||74|
|Exhaust open (EVO ° BBDC)||50||35||82|
|close (EVC ° ATDC)||10||5||42|
|Intake duration angle (IDA °)||240||215||304|
|cam angle (ICA °)||110||102.5||102|
|Exhaust duration angle (EDA °)||240||220||304|
|cam angle (ECA °)||110||105||110|
|Intake / Exhaust overlap (IEO °)||20||10||92|
|Carburetor venturi (CVD mm / in)||38 / 1.50||28 / 1.10||30 / 1.18|
|Dry Wt. (add ca. 23kg / 50lbs wet) (kg / lbs)||205 / 452||218 / 481||180 / 398|
|Published Performance PS / HP||68/67 @ 7000||68/67 @ 8000||57/56 @ 6500|
|Torque (N.m / ft.lbs)||?||60/44 @ 7000||?|
|Published Weight / Power Ratio (kg.PS-1 / lbs.HP-1)||3.01 / 6.75||3.21 / 7.18||3.16 / 7.11|
Maybe Honda’s CB 750 from 1968/9 would be of interest. After all, it is often taken to be the original superbike. (Like everyone else, I tend to forget the post-war Vincent Rapides, Shadows, etc.. That begs the question of what defines a ‘superbike’. But that’s another story.) I couldn’t get all data to put in Table 2 but what there is looks curious. In spite of the CB 750 being crowned with superlatives, its cam timing is a real softy pussy cat – milder even than the ’75/77 Gold Wing. With a 28 mm carburettor, it may not have always gasped for breath but it wouldn’t have been able to climb high mountains of performance. Here, too, Honda was offering a very low stressed engine. Yes, in 1968, 67 horses were quite a performance, but retrospectively it was modest from a 750 cc four-cylinder engine.
Here I suspect that Honda was being honest with itself – by not getting more power out of that CB 750 engine. Was it recognizing that it could build pretty good engines but, like the other Japanese manufacturers, had in 1968 not yet learned to make the frames necessary to contain high engine performance – frames that did not easy turn into epileptic ironing boards on the road?
To illustrate what an aggressive timing can look like, one only has to turn to the Norton Commando parallel twin. Here valves have enormous open-durations of 304° and overlap a whopping 92°. So what? It only produces 56 HP compared to the contemporary CB 750’s 67, but this begs the question of how effective that HP could be. Those Commando horses had to carry around less than 400 lb (180 kg), whereas the CB 750 was saddled with 481 lb (218 kg). The BMW was lighter than this but it still carried 452 lb (205 kg). But why did the CB 750, and its many offspring, survive whereas the Commando (and the British industry) died?
One can only guess an answer. The Commando design-concept had its roots in the 1938 Triumph Speed Twin. This concept was, with much development and little creativity, flogged to death in the following 35-40 years. Just about everything had been wrung out of it – and it had nowhere else to go. It had become overtaxed and over-developed. It was not very reliable and it needed constant tweaking to keep it in trim. Perhaps the keyword about the CB 750 has already been used – under-stressed! Already Honda had established a hallmark in reliability. Yes, the CB still had to be maintained but every time the rider reached for the keys, it was not accompanied by a “Will it? Won’t it?” question. The rider just pressed the electric start button and headed for the horizon without leaving a pool of oil behind him.
One can probably assign the same virtue to that BMW 90S as to the CB 750. Even though this Beemer was the sportiest machine that BMW had produced up to that time, the specification provides decent power without busting a gusset to squeeze every last bit out of it. The flat twin and BMW survived. If it is survival we are talking about, then the Gold Wing must receive all the prizes. The four-cylinders stayed in production for 12 years, with only few changes of design principles of the motor. The 6-cylinder in the 1500 form lasted also relatively unchanged in the engine room for 13 years – and now comes a 6-cylinder as an 1800.
This is saying to me that Honda’s policy of conservative engine tuning has more than paid off over its long history. On the other hand, I would be willing to bet that another 20 or 30 horsepower could be pulled out of this engine. That would mean putting in a much more aggressive camshaft and feeding the beast with a wholly new carburettor system. It would be fun to do – but not very sensible to my way of thinking. First, for the money such modifications cost you could buy yourself a really hot sports bike. Secondly, as suggested, that Honda reliability and long life comes from lack of stress. Push up the ante, and that crankshaft, gearbox and valve train might throw in the towel sooner than you expect.
There is a side issue to mention. So far I have been looking at the mechanical specifications of these machines. However they do not contain allthe information relevant to the pros and cons of performance required by a rider. It is one thing to consider the cost of modifying and engine to provide something special in respect to horsepower or torque. Yet there is the daily bread and butter aspect of the cost of running the bike in its standard form. For instance, information is not readily available about the fuel consumption of these machines. What is available, though, is the type of fuel required. BMWs then as now, call for a higher octane rated fuels than Hondas. In Europe these are 98-octane ‘Super’ and 95-octane ‘Normal’. Just to take Switzerland as an example, ‘Super’ fuel is about 7% more expensive than ‘Normal’. So, again, there are no free lunches. If power is obtained from higher compression ratios that demand high-octane fuel, you have to pay for it. If higher power is found by getting more Suck per intake – ramming more fuel mixture in – then you will have to pay for it. The main neutral operating-cost ways of upping performance would be either to improve the energy release – the combustion process; to improve the translation of this into the reciprocating action of the piston with a more efficient power stroke; or to reduce the power sapping effects of waste heat and gases. Only the latter might bereasonably cheap.
Other power losses can’t be reduced – the pumping losses that underlie the function of the engine. Other losses are also inevitable, even in a well-functioning motor – for instance the friction losses in the engine. The Motion Software texts note that about 70% of all engine friction losses are caused by the pistons moving in the cylinders. Their simulations provide a datum that allows the estimation of these losses. I used this to assess this power loss of the ’75/77 GL1000, up to operating temperature and pulling 80 HP @ 7500 rpm. This loss was about 12 HP! I now have a clearer idea why it is difficult to start a cold engine and have it running smoothly. Drained of lubricant, and when initially lubricated it is with a thick cold oil, the pistons have to overcome frictional forces way above that causing a 12 HP loss when up and running.
This also made me think of that poor little starter motor having to overcome not only this resistance but that of the crankshaft and valve-train as well. And then, what about that battery that has to feed all these demands? It sometimes makes you wonder that the whole thing works at all!
MOTION SOFTWARE SIMULATIONS
Let us be clear about one thing in respect to engine performance simulation. It is impossible to simulate any engine exactly. The purpose of a simulation – it can be looked on as model building – is to provide a tool. It allows the user to ask “What if …?” questions – such as about what might happen if I could fit a Norton Commando camshaft in Gold Wing GL1000, or about the possible consequences of fitting GL1200 carburettors to a GL1100. Such a simulation delivers no absolute answers – only relative ones. One thing is clear, though – the better the simulation program then the better the tool it is.
There is another limitation. Internal combustion engines have been around about 125 years but, in spite of enormous advances recently, the processes going on are still not fully understood. What is known is often associated with very complicated mathematics that challenge the capacity of even the most advanced computer. However, such a computer could not close the gap over what is simply not known. Therefore, even the most exotic program starts out by having to make assumptions and approximations. By necessity, a program run on a desktop PC introduces more approximations. Yet, with such PCs having a performance undreamed of just a few years ago, these additional assumptions stay within reason.
That last issue deals with the theoretical problems of simulation. There are then practical limitations. Even professional-standard programs can’t take the absolutely finest detail into account, purely because of the difficulty of getting the required input data. Take the case of camshafts in general, and of their grind (or shape) in particular. The timing specification is relatively easy to determine and these data are basic information. The amount of lift imparted to the valve by the cam lobe (with the cam followers) is also often available. Such information gives the when and how much of valve opening and closing, but it doesn’t give the how.
The ramps on the cam lobe may have a very gentle slope, opening and closing the valve very mildly. On the other hand, the ramps may be very aggressive, have a very steep slope so that the valve operation is very quick and forceful (with, by the way, those forces also stressing the valve-train more than a mild grind). It wouldn’t be far wrong to suggest that the camshaft of any engine is the most individual, unique part. The mathematics, and the data to use, to model every conceivable camshaft is virtually impossible. Therefore, a simulation programmer has to take a limited number of general options. These are based on current practice and common use in automotive application. They range from cams grinds commonly found of stock vehicles oriented towards modest performance, long life and economical running to hot cams whose only purpose is to produce maximal performance on the track.
A similar approach has to be taken towards the exhaust system after the valve. Again, commonly used configurations of exhaust manifolds, pipes and collector/mufflers are available for choice. Some data for the induction system upstream of the valve are available, such as the carburettor venturi diameter and, maybe, the induction flow rate of the whole system. Again, though, generic configurations of intake manifolds are used to give approximations of the almost infinitely varied details of individual manifolds.
The specifications provided in the various Gold Wing workshop manuals did not include induction flow rates. No doubt Honda or Keihin have the results of practical flow-bench studies in a drawer somewhere – but they aren’t available to the hoi-poloi like you and I – well, on asking Honda (Switzerland) I was told that such data, if available, would be treated as company secrets. Rather than guessing (for which I had no basis whatsoever), I made what I thought was a logical estimate.
Earlier on I calculated an estimate of the amount of charge that got rammed into the cylinder. (Formulas (5) above gave a volume of 19.79 in3 or 324 cc). This could only get into the cylinder while the intake valve was open. Taking 7’500 rpm as my reference point, it is no great hassle to calculate the time that an intake valve is open during each cycle – the IVOT, intake valve opening time. With the volume and the time, it is an easy step to work out the average flow rate though the intake system of each cylinder. Multiplying by four gives that flow rate for the whole engine. Also from the flow rate and the venturi dimensions, the average velocity of the air through the carburettor can be calculated. These various estimates, with the exact GW specifications from Table 1 were fed into the Motion Software simulation program to obtain simulated power and torque curves over the rpm-range. I have listed the calculated estimates and the peak HP and torque values in Table 3. (I only use peaks as representative because of the mountain of data that makes up such curves.)
I must admit that I never really thought about some things before I started playing with these things. I mean, I never imagined that valves, on the ’75 GL1000 for example, are only opening for about 1/100th second – 10.44 ms to be exact – when running at 7’500 rpm. (My curiosity awakened, I took this calculation a step further – just for fun. The valve starts at zero kph/mph. It accelerates up to travel its 8.5 mm of lift, stops at 0 kph/mph, then accelerates down to reseat at 0 kph/mph. That is 17 mm in 10.44 ms; or 5.86 kph (3.66 mph). That is the average speed, with the peak reaching double that – 11.72 kph (7.3 mph) – and that 3’750 times a minute. That is quite a beating that the valve train gets. Some Gold Wings have been doing that for more than 25 years!)
Moving on to the ‘78/79 model, the intake valve opens fractionally shorter, but the smaller venturi makes the mixture move faster. This higher induction velocity gets more mixture into the cylinder through that ramming effect. Moving on to the 11 and 1200, they have more capacity pulling in mixture and now a 30 mm venturi. This continually increased the mixture velocity and, through ramming, the induced volume as reflected in the induction flow rate. If the common wisdom is correct, the main consequence of improving induction is to increase torque. (As discussed above, this could also increase horsepower – but that would depend on the portion of the rpm band where the torque increased.)
Turning now to the actual simulations – it is clear that, in comparison to the published performance data, the simulated values are all too high. Now, I reckoned above that Honda built engines that are very conservatively configured. I set the conditions for the simulations as conservative as I could. On the advice of Motion Software’ support group I also toned down what I thought were the best estimates of the GW cam-form. My values came down to those given in Table 3, but still remained high. So, that engine really must be a mild pussy cat! – milder than even Motion Software allow for.
But this didn’t worry me unduly. I had no problem in accepting Motion’s advice that the idea was not to reproduce performance exactly (though that would be nice), but to get an idea about the performance of different engine lay-outs and/or tweaks. ‘Reading’ the specifications suggests that the first Gold Wing started out as a torque machine and not a horsepower wizz – and that this principle was extended all the way through. The simulation shows that, from the ’75 GL1000 to the ’87 1200, peak horsepower increased by 117%. The same development led to a 128% increase in peak torque. This confirms, with reasonable accuracy, the published figures that show a 118% in peak horsepower and a 131% increase in torque. (And from the ’75/77 GL1000 to the published data on the 2001 GL1800? – a 48% increase in horsepower and a 183% increase in torque!)
|GOLD WING ENGINE SIMULATIONS||GL1000
|Carburettor venturi diameter (CVD mm / in)||32 / 1.26||31 / 1.22||30 / 1.18||30 / 1.18||30 / 1.18||30 / 1.18|
|Calculated values @ 7500 rpm
Intake valve open time (IVOT ms)
|Average induction flow velocity (IFV m.s-1 / ft.s-1)||95.2 / 312.4||108.5 / 356.0||122.9 / 403.2||122.9 / 403.2||146.5 / 480.6||149.8 / 491.3|
|Average induction flow rate (IFR m3.min-1 / cf.min-1)
(All 4 cylinders)
|7.456 / 263.03||7.965 / 280.97||8.339 / 294.33||8.339 / 294.33||10.054 / 354.89||10.277 /362.78|
|Simulated performance PS / HP||79 / 78 @ 6500||85 / 84 @ 6500||89 / 88 @ 6500||89 / 88 @ 6500||92 / 91 @ 6500||96 / 95 @ 6500|
|(Motion Software Dyna 2000) Torque(Nm / ftlbs)||92 / 68 @ 5500||103 / 76 @ 5000||107 / 79 @ 5000||107 / 79 @ 5000||114 / 84 @ 5000||118 / 87 @ 5000|
If you remember, apart from the fun of exploring this, for me, unknown territory and the challenge of finding out just how little I knew or falsely preconceived, I wanted to get some basis for judging the consequence of modifications. I am not really interested in turning our 76s into drag-strippers (that is for private clubs only! J ) I wanted to know what could happen if I ever had to fit non-OEM parts.
There is a tip on where to look first in the specifications – that modest intake-exhaust valve overlap of only 10°. With so little time to bring any advantages, it looks like scavenging by the exhaust is not a very important aspect of the GL1000 performance. Without spending several hundred dollars to try this, the simulation program can be called up. I set up that ‘mild’ ‘75/77 model and then ‘fitted’ the most radical exhaust system offered – large stepped-tube race headers, that are probably highly street illegal in reality. The simulated peak HP went up from 78 @ 6500 to 93 @ 7500 – an increase of only 19%. Torque (leaving out the units) only increased from 68 @ 5500 to 74 @ 5500 – not quite 9%. So, maybe it wouldn’t matter too much what sort of non-OEM exhaust I fitted, so long as it wasn’t as constricted as a cat’s posterior.
If, however, I could replace the individual intake tracts with a single plane manifold that had a 30% better air-flow, the peak torque would only rise by 10% to 75 @ 6500. Horsepower however would jump by 33% to 104 @ 8500. That is considerable. Therefore, any replacement of the carburettor system could have striking consequences.
A quite different modification – if I could run a GL1100 camshaft in the ’75/77 (and not have any problems with the 0.3 mm extra valve lift), then simulated performance changes only a little, with both HP and torque increasing by 5-6%. Here I think the only notable effect of this modification would be to lighten my wallet.
There is a final reservation to make about the foregoing. I only referred to peak performance values – either real or simulated. No engine performance, no suggestion of the riding experience can be captured by these alone. The power curves over the range of engine speeds provide a fuller picture. Official data are rarely available. To add those from the simulations would turn make this thin book into a tome. Nonetheless, I can invent a tweak that would make knowledge of those curves crucial. Take that ‘75/77 GL1000 producing 80 N.m (59 ft.lbs) of torque at 6’500 rpm. Now imagine that after my tweak it produced only 75 N.m – but 75 N.m now available from 2000 to 8000 rpm. The peak has dropped a fraction, but is available over the whole of the useful rpm range – forming a very high plateau. I could probable save weight by throwing away the gear box and having a direct drive! However, it would only be the power curve that could confirm the advisability of that measure.
All in all, then, the major profit from this simulation was to jolt me into thinking about things I didn’t know – or thought I knew, falsely. Also important is the fact that it helps point me in the right direction and to pose some relevant questions. I don’t deceive myself that I now understand these processes that influence performance. For the moment it is enough for me to know that they exist. Lastly, the fact that simulation results are not absolutely exact numerically is not the issue. The program helps me adhere to that quotation from the famous American statistician, John Tukey, who I have cited before:
Far better an approximate answer to the right question, which is often vague, than an exact answer to the wrong question, which can always be made exact.
9th December 2000
1976 Honda GL1000 K1 *
1976 Honda GL1000 K1 *
1980 Honda GL1100 Std *
1981 Honda GL1100 Std *
1982 Honda GL1100 DX *
1982 Honda GL1100 DX+ EML GT1
1987 Honda GL1200 AH *
1994 Honda CB500 *
1964 Norton 650 SS