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%).

11-30-2005, 03:16 PM	#1
Craig K. Nothing new here Join Date: Dec 2004 Location: Senoia, GA Posts: 2,990	Dyno testing gear difference? Has anyone hear ever dyno tested before/after a gear change? Does it make any difference in the power / torque curves? __________________ 1974 Triumph TR6 1985 Monte Carlo SS 1986 Mustang GT 2011 KIA Optima GTS

11-30-2005, 05:18 PM	#2
Wicked Friends Join Date: Dec 2004 Location: Pell City, AL Posts: 1,371	Re: Dyno testing gear difference? 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. __________________ 2001 Cobra 'Vert Procharged and Intercooled 455rwhp/441rwtq Work Car: 2005 Honda Odyssey 400 whp Turbo V6, 6-speed, full cage, H&R Suspension, Brembo Brakes

11-30-2005, 05:37 PM	#3
QWKSNKE 3v's are slow Join Date: Dec 2004 Location: Here and There Posts: 17,152	Re: Dyno testing gear difference? 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 __________________ 2009 Porsche Carrera S 2008 ///AMG C63.. Eurocharge Tune. RIP 2019 AMG GLC43..wife's 03 F250 SD.. Edge Evo, AFE Stage 1 CAI 08 GT. JBA axle back, FRPP springs, FRPP swaybars.. daughter's 01 Cobra vert... wife's I need a new toy

11-30-2005, 06:10 PM	#4
Wicked Friends Join Date: Dec 2004 Location: Pell City, AL Posts: 1,371	Re: Dyno testing gear difference? Yep... That's the efficiency I'm talking about. __________________ 2001 Cobra 'Vert Procharged and Intercooled 455rwhp/441rwtq Work Car: 2005 Honda Odyssey 400 whp Turbo V6, 6-speed, full cage, H&R Suspension, Brembo Brakes

11-30-2005, 06:49 PM	#5
Craig K. Nothing new here Join Date: Dec 2004 Location: Senoia, GA Posts: 2,990	Re: Dyno testing gear difference? Thanks, a friend at work and I were discussing what changes would be seen. __________________ 1974 Triumph TR6 1985 Monte Carlo SS 1986 Mustang GT 2011 KIA Optima GTS

12-04-2005, 09:00 AM	#6
coupe Super Moderator Join Date: Dec 2004 Posts: 6,313	Re: Dyno testing gear difference? 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%). __________________ " If you can't explain it simply, you don't understand it well enough. " - Albert Einstein