Busa specs

[Admin]

I know it has been gone over 1000 times, but what is the maximum torque number a busa puts out at the drive sprocket...Im trying to determine what my fnr has been proven to...They have been buas'd with 1:1 gearing to the trans input shaft, Just wonder how much reduction in my little motor i could achieve to the trans input shaft....

[Yoshi]

the busa specs calls for 187 hp and 99 foot pounds of torque at the crank.

I have a dyno chart here with actual rear wheel numbers, 151.17 max hp and 86.14 max torque..

the red is the stock numbers, the blue was the initial pull on a motor I had built that ended up putting 220hp to the wheel, but I can't seem to find that sheet, although I have a sheet showing 212 and 105.96 foot pounds of torque, he had problems getting traction in 5th. gear over 3/4 throttle...

[Admin]

the busa specs calls for 187 hp and 99 foot pounds of torque at the crank.

I have a dyno chart here with actual rear wheel numbers, 151.17 max hp and 86.14 max torque..

the red is the stock numbers, the blue was the initial pull on a motor I had built that ended up putting 220hp to the wheel, but I can't seem to find that sheet, although I have a sheet showing 212 and 105.96 foot pounds of torque, he had problems getting traction in 5th. gear over 3/4 throttle...

So the torque is figured thru the reductions etc? or is that the actual measured at the rear wheel?

[Yoshi]

[Admin]

so the 80 some ft lbs of torque was at the wheel, what happens to the multiplication thru gearing to get what fabber always says torque is multiplied to?

[fabr]

that dyno chart is measured at the wheel, the crank numbers are higher...

That is CALCULATED usable torque that is supplied to the rear wheel that takes into account parasitic losses through the geartrain due to it being measured at the rear wheel.The ACTUAL crank #'s would be higher only because they would not have the geartrain losses to consider. Since there is no way to couple a busa crank directly to the dyno ALL crank numbers stated are calculated approximations. 

[Yoshi]

[fabr]

[Admin]

So at the highest reduction, what would the 99lbs of torque equal at the drive sprocket?

[fabr]

Your gonna have a lot higher torque number in the lower gears because the ratio is lower, but that ratio basically stops at the final drive, or actually the center of the wheel, you loose torque as you go farther out on the wheel. You would have a lot higher torque number if the drive train was hooked directly to the dyno, the 24" tall wheel eats up a big chunk of that torque.

Think of a wrench, you can put hundreds of pounds of torque on a 3/8 bolt by hand and spin it easily, even stripping the threads if you wanted, but if you had an adapter to attach to a  2 foot in diameter bolt head, and you still had the same torque wrench, which was a smaller than the wheel, you couldn't apply much torque at all and wouldn't get the bolt snugged very tight.  That why you always strip smaller bolts a lot sooner than a bigger bolt. The high torque numbers are seen by the chain and gearbox which is why they always break, not the outside of wheel, ut given enough power and traction, you could break the studs attaching the wheel to the drive train because the closer you go to the center of that tire, the more torque you will see..

Yoshi your understanding is mostly correct but in red is not.Any torque multiplication stops at the rear wheel axle but with a 24" tire you only lose 1/2 of the actual FT lbs of torque at the rear axle...24" /12" =2:1. That is a lot but a lot to the extent that I felt the rest of the reply would indicate.
Say the ACTUAL measured tq at the rear wheel was 400#' the tq at the rear axle would be 800#'.

[Yoshi]

Another easy way to think about it is a car, you can turn a tire by hand and cause the car to roll, but if you try to grab the  axle and turn it by hand, the car won't roll.  You may only need 50 foot pounds of human supplied torque to turn the tire and roll the car, but you will need a lot more torque to turn the drive train to roll the car.  So it may take 50 foot pounds of torque to turn the wheel, and that may put 300 foot pounds of torque to turn the drive train (just like a wrench).  The torque goes up when you use the bigger diameter tire to turn the smaller drive train, it goes down when you use the drive train to turn the tire....

[fabr]

I don't have the true 1st gear ratio here but assume this scenario.80#'x1.596 primary reduction x2.5:1 first gear times rear axle ratio of 5:1=1596#'to at the rear axle/by 24"tire 2:1 RATIO increase=798#' AT THE TIRE SURFACE.

[Yoshi]

Yoshi your understanding is mostly correct but in red is not.Any torque multiplication stops at the rear wheel axle but with a 24" tire you only lose 1/2 of the actual FT lbs of torque at the rear axle...24" /12" =2:1. That is a lot but a lot to the extent that I felt the rest of the reply would indicate.
Say the ACTUAL measured tq at the rear wheel was 400#' the tq at the rear axle would be 800#'.

I believe I am correct.  Lets make it simple, if you have a 14 tooth front sprocket and a 60 tooth rear sprocket, you have a 5:1 ratio, which means you are putting 5 times the amount of torque to the center of the 60 tooth sprocket as you are the 12 tooth sprocket, correct?  Since your putting the highest number of torque at the center of the biggest sprocket, a straight line from the center of that sprocket via a drive axle to the wheel will see the same number of torque, putting the highest number of torque at the center of the wheel, you then loose torque as you go out to the edges of the wheel.

Granted the most torque is only applied when the axle is straight to the wheel, since you loose hp and torque as you have angle, but worse case senerio, there will always be points where the axles is straight and applying th most torque possible to the wheel...

[Admin]

I just want it at the sprocket, the motor i am debating using is 80 lbs at the crank, Im trying to figure out how much i can gear it into the trans, 1.2:1 1:1 etc.... I dont want to expierment with any more torque than i know has been put thru them....But at the same time id like to take advantage of every bit of gearing i can...

[fabr]

WHich sprocket? Countershaft I assume?