Shamu

Hi folks:

I was told that you should dyno in the gear that is closest to 1:1 which makes sense. I chk'd the S2K's ratios and this seems to be 5th gear (0.97:1) rather than 4th gear (1.16:1).

So is there a reason why most dyno's here did it on 4th? I believe this throws off accuracy of our dyno results...is there a reason why we don't dyno in 5th?

cdelena

I suspect it is because people assume that 5th gear is an over drive.. I don't think it is, I think you must apply the reduction ratio so it is .97 * 1.16 resulting in a 1.1252 ratio.

twohoos

Even if 5th was an overdrive -- so what?

Shamu

do you have to apply this 'reduction ratio' to the 4th gear as well, and if so, won't this result in even a farther 1:1 relationship than 5th?

Penforhire

Wouldn't another important factor be the speed at which you are racing the dyno drum up to? I imagine it is most accurate, maybe even safer, over a specific rotation speed range (lower than 5th gear). I asked my local shop when I dyno'd and they ran mine in 3rd gear.

Wesmaster

I don't recommend 3rd gear, noticably lower HP (can't say that it's not more true, though <shrug>). See the lowest line on the set of HP lines, the top set - bottom is torque, on the chart below. They ran mine in 3rd on one run just for a test.

Shamu

The explanation I rec'd (and this makes sense to me) is that the closer you are to 1:1 ratio, the more accurate your dyno given 1 revolution at the crank, is 1 revolution of the drive shaft. Of course, there wil still be drivetrain loss, but this can now be easily calculated (percentage wise) given a 1:1 ratio.

I agree with Wesmaster -- don't dyno in 3rd as the result is inaccurate and erratic...

Pinky

Well when I ran my car on the dyno they said use 3rd because Its a faster run to redline and puts less strain on the engine your pushing a 1500 lb drum. Also I made them run it back to back 3rd and 4th I gained 1 foot pound tq. and 0 hp. They said see......very little if no change!

After it was done he also said well there you go 4th gear 1 more foot pound and you really strained your engine.(he don't know me very well do he!)

mingster

no changes when i dynoed 3rd/4th gear - nada.