9 inch to quick change gear ratios ????

[ump29]

i recently switched to a quickchange from a 9 inch.. i have hear people say you have to run more gear with a qc to get the final drive you were running in a 9 inch.. so my questions is if i was running a 600 in a 9 inch what should i start with in the qc... or does anyone know a formula to figure it out... the quickchange has 4.86 ring and pinon..

[killer bee]

Usually about 20 pts deeper. You should start out around a 6.20 and be close.

[dirttrackrocker]

Can someone explain why??? Lets say all things are equal, your car weighs the same with the QC as it did with the 9 inch, and your using the same weight axles. Why would final drive ratio need to change??

[charcoal01]

because it takes more horsepower to turn a quickchange. so you need to run a little more gear

[dirttrackrocker]

I'm guessing because of the extra shaft and gears in the QC ??

[sj valley dave]

I heard that it was roughly 3-4%...That's around 20-25hp on a 600 hp engine...does that sound right, and if it is, 20 points seems like a lot....

[Graff Spee]

If you think that it makes a differance, try this out. Ford 9inch with GM 12bolt gearset. Its big in dragracing. You get the unsprung weight of the 9inch over the quickchange. You also get the GM gear that has much less drag than the ford gear. They sell them in most popular ratios. You could even go with an aluminum carrier and housing! I have seen no measurable change when going to a QC over a 9. Thats just me though. Good luck! You will love the QC!

[Egoracing]

When we ran asphalt and went from a 9 to a QC the ONLY reason we changed the ratio was because we could not get it in a 9 inch. When we first put it in we ran the exact same gear and turned the exact same RPM on the chassis dyno there was not very much of a difference.

[HEAVY DUTY]

When we ran asphalt and went from a 9 to a QC the ONLY reason we changed the ratio was because we could not get it in a 9 inch. When we first put it in we ran the exact same gear and turned the exact same RPM on the chassis dyno there was not very much of a difference.

I remember once when Mr. Hendren posted that a 9" lost 15% and a quickchange lost 17% thru the drivetrain compared to the engine dyno.That would also be assuming that each rear end was set up properly.Most modifieds are over horsepowered at most tracks anyway.There aint no way I would give up my quickchange for 2%.Im way too old to change them 9" gears now.

[Egoracing]

I remember once when Mr. Hendren posted that a 9" lost 15% and a quickchange lost 17% thru the drivetrain compared to the engine dyno.That would also be assuming that each rear end was set up properly.Most modifieds are over horsepowered at most tracks anyway.There aint no way I would give up my quickchange for 2%.Im way too old to change them 9" gears now.

2% of our 600hp is only 12 hp and that is almost withing the error on the dyno. Also it was REALLY nice to be able to qualify with a a 5:60, 67, 70, 74 or 78 and race a 5:83 than qualify on a 5:83 and race on it!