I dyno'd my car at at 7's only racing at Buttonwillow this past weekend but they wouldn't let me dyno in 4th gear so I was limited to only 3rd gear (1.391 ratio). Car made 338 in 3rd gear.



Back in June it dyno'd in 4th gear (1.000 ratio) 343.



I recently fixed some sticking actuators in the turbo system which completely smooth out the power line.



Does anyone know a correction value I can plug into the 1.391 gear as if i had dyno'd in a 1.000 gear?

 

curious as to why the limitation to 3rd...

 

There isnt really a correction value, or at least Ive never heard anything. The difference in power comes from the engine being loaded slightly less, instead of the gear ratio directly. The two runs were also on different dynos, and they wouldnt produce identical numbers, even if the car made identical power on each one(which is unlikely). If you want to compare before and after, you need to go back to the original dyno to get any sort of semi-accurate results. But even the day to day changes in temp, humidity, and atmospheric pressure will affect the hp.

 

i made 335 whp in 3rd and then 359 whp in 4th on the same dyno. so i guess its about 6-8 % gain.

 

Paraphrased from a couple posts on another forum:



"A Dynojet chassis dyno is an accelerometer. It measures the rate of acceleration of drums of known weight and calculates the amount of power required to accelerate them at that rate. From this and monitored engine rpm it calculates torque, which is why they don't need to know your gear ratios or tire size.



The reason pulls are made in 4th gear with a manual is because it is 1:1 and usually shows the smallest drivetrain loss. The 1:1 ratio also makes the pull take a reasonable amount of time in order to give the computer sufficient data points without keeping the motor working too long."



In other words, your gear ratio doesn't really matter, except for the effect it has on the load on the engine and therefore boost response and level, which would affect measured power output.