The Simulation of Gold Wing Engines
Trevor White
Classic Wing Club
INTRODUCTION
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.
TYRES
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 A and 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.