From what I understand the OEM gear ratio for the rear end is 4:10. I'm going to be running 600RWHP so I'm thinking about lowering the gear ratio so I can stay in each gear longer. My question is what gear ratio should I use, 3:91 or 3:63? S2kpuddydad is building the rear end and said that either would work but I would be the first to use a 3:63. Can anyone offer any insight or experience? I'd like to know if anyone is running the 3:91 and how they like it.

*Note: My car is not daily driven, tracked or dragged. It's driven only on nice days and I like a lot of top end.

Thanks,
Chris

 

3.63 sounds awfully low. I understand that the power is there but it seems like it will take forever to reach the meat of the power band.

My vote is on the 3.91 rear.

 

http://www.turnzero.com/technical_resource...gear_calculator


play with the gearing. i would do 3.90 personally. i kinda feel 3.63 would be too deep. 3.91's and a 275-35-18 can hit 115mph in 4th and 141mph in 5th. that should be plenty!

 

Is that the numbers you got from the gear ratio calculator? Something doesnt seem right because i hit right around 118 mph at the top of 4th gear (9000 rpm) with my 275/40-18's and 4.08 gears on the dynojet.

 

kewlwhip is ap2 tranny. yours is ap1?

 

^That would probably make a difference then. Are gears 1-4 that much different on the AP2? I thought the AP2 tranny had a higher gear ratio than the AP1 due to having a little more TQ which would make for higher speeds in each gear. Yeah, I have the AP1 tranny.

 

The only guy I know who has a lower gear is Soul Coughing, he should be able to tell you better than most. I think he has the 3.90.

 

Thanks for the link to the calculator!

Using search I found that the tranny ratios are as follows:
Primary Gear Reduction - 1.208
1st gear - 3.133
2nd gear - 2.045
3rd gear - 1.481
4th gear - 1.161
5th gear - 0.942
6th gear - 0.763
Reverse - 2.800
Final Drive Ratio - 4.100

 

1-4 are the same in both trannys, but reduction gear is different.

if anything, gears are shorter in ap2

 

Gotcha. I just checked the gear ratio calculator and gears 1-4 on the AP1 and AP2 seem the same from what I can tell. The dynojet must have been off on speed then as with my setup on the calculator, 275/40-18 tires, my 4th gear speed at 9000 rpm tops out at 126 mph with the 4.08 rear gears.