Changing gear ratio
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Teching In
Joined: Oct 2005
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From: bismarck il
Changing gear ratio I have a 73 Corvette with a 2002 LS1 and a 4l60e trans. The gear ratio now is 3:08 and I bought a rear end out of a 79 with a 3;55 gear. I have been told that my vette needs a lower gear to keep the power band up with the LS1. What rpms will it turn at 65 mph ? Thanks Charlie.
http://www.f-body.org/gears/
Just select "1998 F-body A4" and that will give you your transmisison gear ratios, set "Red Line RPM" to 7000 rpm and play with the tire size and rear end gear ratio until you see the RPM you want at 65 mph. Using 30" tires with my Viper T56 and 4.56 rear i turn the exact same rpms i do in my 94 using 3.73s with a 93 trans (viper ratios) and a 26" tire. Both are equivalent to a T56 Fbody with 4.10 gears and 26" tires which is equivalent to a 4l60E fbody with a 3.73 rear and 26" tires. I would think you'd be running a 28" tire and 3.73s would be fine for you if you want to keep it geared down a little.
Just select "1998 F-body A4" and that will give you your transmisison gear ratios, set "Red Line RPM" to 7000 rpm and play with the tire size and rear end gear ratio until you see the RPM you want at 65 mph. Using 30" tires with my Viper T56 and 4.56 rear i turn the exact same rpms i do in my 94 using 3.73s with a 93 trans (viper ratios) and a 26" tire. Both are equivalent to a T56 Fbody with 4.10 gears and 26" tires which is equivalent to a 4l60E fbody with a 3.73 rear and 26" tires. I would think you'd be running a 28" tire and 3.73s would be fine for you if you want to keep it geared down a little.
If you are keeping your engine stock, no cam, you can use the 3.55s or even the 3.08s. Just so you know the stock rear ratio for all Autos from 1993-1997 was 2.73 with an optional 3.23. In 1998 i think they just became 3.23. It an unmodified engine you really dont have to change the gear ratio but it would help ALOT to get the car moving. I turn 2000rpm at 60mph, and about 2500rpm at 75mph in my 3700lb 94 camaro with a T56 and a rear ratio equivalent to 4.10s and 28" tires on your setup and i get 23mpg on the highway (75mph) and mixed driving i get 19-20. But again thats with an Lt1 which is far less efficient but still just a bolt on motor.
