Thanks Revlis, you're a breath of fresh air! Yup we're metric here but not out of the dark ages completely.
This is GEOFF by the way, not Jim who owns the bike in question. I was talked out of cancelling my membership by cache who explained that these sorts of cheesey postings cause this exact problem ALL the time. I get the impression it's the non-cheeses he'd rather keep so here I am sorry.
Those torque figures look fine to me. If they were crank figures I'd be horrified, but as they show a final gearing of 4.441 that is the amount by which the crank torque was multiplied just as it is the factor by which the revs were reduced from crank to wheel.
So the rear wheel was spinning at 1/4.441 times crank speed and the crank torque was 551/4.441 = 124lbs/ft. The stock busa is 102lbs/ft at 7,000, adjust for the dyno overreading 33% and at the crank Jim is only making 93lbs/ft which is slightly low if anything but the 33% is rough.
If you can't exactly reconcile their 4.441 final drive with the Busa's stock ratios it's because they remove the rear wheel and provide their own rear sprocket with a different number of teeth. The bike was in fifth as all Busa runs should be because as you guys will already know you have to avoid the famous timing retard in the lower gears and the limiter in sixth.
We'll calculate the rear wheel horsepower from the rear wheel torque because I love doing this! Forgive me if I try teaching anyone how to suck eggs, this is aimed at 'good eggs' that suck
Let's put a 1 foot spanner on Jim's back wheel while the engine is pulling 7,484 in the 4.441 overall ratio gear. Measure the circumference the spanner scribes in one rev to determine distance per revolution, 75.39816 inches. Determine the wheel speed - from their final drive ratio it must be doing 7,484/4.441 which is 1,685rpm.
Sanity check - 124mph road speed is shown on the torque graph. That's 198kph (sorry!) which is 198,000 meters per hour which is 3,306 meters per minute, divided by 1,685rpm which is what the wheel is doing gives a wheel circumference of 1.96 meters which I think is pretty right but if not it doesn't matter because the wheel isn't on the bike on this dyno, so their road speed relies on them entering the circumference anyway and they may not have been right. But that's really close and just suggests nothing is horribly wrong so far.
Okay so the wheel is doing 1,685rpm and I'm now satisified that this correlates to their indicated road speed.
In one minute therefore the tip of the spanner will have travelled 75.396 x 1,685 inches = 127,057 inches (10,588 feet in one minute).
If we now apply our pressure of 551 lbs to the tip of the spanner, given the handy 1 foot length of the spanner I chose, we are now applying 551lbs/ft of torque to the wheel over a distance of 10,588 feet per minute.
One horsepower is the effort required to raise 33,000lbs a distance of 1 foot in 1 minute. What we are now doing is applying 551lbs of force over 10588 feet in one minute.
So we are travelling 10,588 times the distance and lifing 551/33,000 of the weight of one horsepower.
That equates to 551/33000*10588 which is 176bhp. Correcting for the 33% overreading dyno we get 132bhp at 7,484rpm which I think is spot on.
More importantly, if you now look at the horsepower graph and look up 176bhp you will find the revs at that point are 7,484rpm (well, hard to be exact with a rained-on inkjet printout but real close).
Do you guys not get to see the raw rear wheel readings on your dyno runs or something? Or do you not get your bikes dynoed? From all the talk it sounds like everyone's a dyno expert so I'm surprised you're not familiar with rear wheel torque figures and the effect gearing has on them.
Finally, let's change gear for a laugh.
At the same 7,484rpm in first gear we are obviously still making the same horsepower at the wheel as we were in fifth give or take one or two for losses or gains perhaps. The ratio has changed from the 1.136:1 of fifth to the 2.615:1 of first. That reduces the wheel speed from 1,685rpm to 1685 x 1.136 / 2.615 = 732rpm, with an attendant increase in torque due to the increased mechanical advantage to a new high of 551 x 2.615 / 1.136 = 1,268 lbs/ft.
Which is why they retard the timing in the lower gears, and why you can wheelie first easily but not sixth despite making the same horsepower in all gears at a given engine speed.
Sorry if this is all basic, I get carried away, but there may be some readers for whom it is new and interesting that that - not pointscoring - is why we're all here isn't it?
Geoff. Not Jim. Geoff.
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. . . . . man oh man . . . . as usual . . . no common opinion. Lots of female-like *****ing though. Can't we all tune in harmony?
