i have a 1969 firebird with a 455 with around 500 hp,th400 transmission,9" currie rear end with 3.73 gears with a 26" tall tire,it runs about 2700 @55 and @3200@65.i wanted to drop the rpm's down by about 400 by using either 3.08,3.21, or 3.31 but i didn't know if these lower gears would make it dog.is there anybody out there with a similar set up.no racing,just street use and countryside cruising,but i still want to have fun with it.thought about overdrive transmissions but pricey for reliability.
rear gear selection
- Thread starter burnbird
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It depends on what cam, intake and carb you are running, they were all designed to run best in a particular RPM range. The 3.08 and 3.21 I wouldnt go near and 3.31 might be OK. You probably will be unhappy with anything less than a 3.55 and that might not be worth the time and money.
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thats a very healthy cam and large carburetor, definitely nothing less than the 3.31 or it will not run well at low RPM. is the carburetor a double pumper or vacuum secondary? If double pumper it will not like low numerical wise gears.
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less wear on the car ,a little better milage,it also seems a lot quieter at 45 mph than 55 to 60 mph.thats why the 400 rpm.i guess i want the best of both sides without giving up any performance.3.31 would do that but i haven't found any for the 9" yet