Lowering gear ratio for turbo
02-20-2010, 03:28 PM
#1
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Lowering gear ratio for turbo
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
*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
02-20-2010, 04:41 PM
#2
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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.
My vote is on the 3.91 rear.
02-20-2010, 04:42 PM
#3
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!
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!
02-20-2010, 04:49 PM
#4
Originally Posted by camuman,Feb 20 2010, 08:42 PM
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!
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!
02-20-2010, 05:33 PM
#5
Originally Posted by Spoolin,Feb 20 2010, 08:49 PM
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.
02-20-2010, 05:38 PM
#6
^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.
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02-20-2010, 05:46 PM
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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
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
02-20-2010, 05:50 PM
#10
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.