The Simulation of Gold Wing Engines and/or Understanding - Trevor White...continued
|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|
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!)
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 wouldnt matter too much what sort of non-OEM exhaust I fitted, so long as it wasnt as constricted as a cats 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 6500 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 didnt 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 dont 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.