Trying to decide what gear to run behind a stock 331 Chrysler Hemi in a Model A with automatic transmission. Tire height will be 31.5 inches, Calculations at 75 mph: Gear RPM 2.75 2259 3.00 2464 3.25 2670 3.5 2875 Will spend a good amount of time on the highway. Any recommendations are greatly appreciated. Thanks.
Some info on the engine specs would be helpful, but if highway running was my main concern, I would be going for the 2.75 gear set. A properly built 331 will have plenty of torque down low to get a light weight Model A moving with that tall of a rear gear.
My 32 has 3.48s with 31.5s and no overdrive. Different engine, but still a small V8. I like the combo. Its not too buzzy while giving enough gear to move well with only 300 (if that!!) or so HP.
Slush box, or stick shift? It will make a difference in how the car drives. I'd stay in the 3.25:1 to the 3.50:1 range with a stick shift. -Dave
FrozenMerc: Completely stock rebuild is what I was told. town sedan: automatic transmission(no overdrive)
the higher ratio worked for me for long distance 75 plus speeds something like 3000 RPM the early hemis don't like the higher revs. mine was a 331 hemi 750 cfm carb, GM ignition, th400, GM 12 bolt posi 2:90 with that set up I could buzz up over 120 without going over 4500 RPM
I am building a 330 Hemi for my truck. I already had built the 9 inch posi with 3:70 gears. In-between is a A518 overdrive automatic. If I was not running an OD I would not have exceeded 3:55. If it helps.
For extended highway use I'd keep the rpm below 3000, not beause the engine won't tolerate more, but just because of the inherent noise generated. .
I agree with 73RR. (Pretty much always) Side note. I'm doing a 354 and hoping to be cursing at 75 at approx 2300, but am quite a bit away from testing it out.
After talking with 73RR I have chosen to go with 3.25 gears. Thanks again to all the members that responded.
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