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View Full Version : Dyno testing gear difference?


Craig K.
11-30-2005, 03:16 PM
Has anyone hear ever dyno tested before/after a gear change?
Does it make any difference in the power / torque curves?

Wicked
11-30-2005, 05:18 PM
It will make a difference if you are looking strictly at torque at the rollers, but the dyno calculates gear ratio using dyno rpm and engine rpm and then uses that to calculate engine output minus losses.

So the only change you will see on a dyno graph from a gear change is the change in gear efficiency. Lower ring and pinion gears are less efficient due to higher pressure angles.

QWKSNKE
11-30-2005, 05:37 PM
Seems to me that Brian Bradford (10secsnake on other forums) told me one time when he and I were talking about it that going from 4.10's to 4.56's cost him around 5 rwhp on the dyno graph

Wicked
11-30-2005, 06:10 PM
Yep...
That's the efficiency I'm talking about.

Craig K.
11-30-2005, 06:49 PM
Thanks, a friend at work and I were discussing what changes would be seen.

coupe
12-04-2005, 09:00 AM
Think of a dyno pull to 6k RPM with the same motor and two gear ratios: 2.73 and 4.56.
The 2.73 will take longer to spin up, but the end speed of the roller will be high. The 4.56 will spin up alot faster, but the roller speed will be alot less than the end speed of the 2.73's.
The dyno software will theoretically calculate the same power out of these two pulls because the one that took longer did more work (power = work * time) but that small power loss will show up too.

On a high-hp motor, 5-10 hp is probably within the allowed deviation on a dynojet...(I think they claim +/- 1%).