gearing questions

[macho781988]

ill have a 360 4spd od trans 8 3/4 in my coronet and i want a 25 or 26 inch tire at 3.91 gears wat rpm would i be spinning at 60 mph? should i go down to 3.55s?

 

[68X426]

ill have a 360 4spd od trans 8 3/4 in my coronet and i want a 25 or 26 inch tire at 3.91 gears wat rpm would i be spinning at 60 mph? should i go down to 3.55s?

I assumed your OD is .73.

With 25", 3.91, at 60, the rpm is 2302.
With 26", 3.91, at 60, the rpm is 2132.
With 26", 3.55, at 60, the rpm is 2006.

Several factors to consider: your type of driving (daily driver, highway, city, racing, cruise, distances, hills), your style of driving (heavy footed, laid back), and most importantly your cam's power range.

If the cam is built for a 2400-5500 rpm range you will be forever downshifting and/or lugging the motor. If the range is say 1800-5000 then maybe the 3.55s will work (depending on type and style).

The goal is to coordinate the cam and the gearing for the optimal drivability. You have some flexibility with tire height, but the cam's range is critical in your choice of gear ratio.

 

[Meep-Meep]

I agree. Those late model OD 4 spds have a pretty wide gear spread so pick a cam with a wider lobe separation to spread out your torque curve a bit. Something in the 114 deg range or higher. The factory 340 cam may be a good choice but select the one for your compression ratio.

 

[696pack]

If your using the old original Mopar aluminum case OD trans understand that it is NOT a good choice for a performance application and does not hold up well nor does it have a good performance gear spread.

 

[macho781988]

ill only push 300 horse or less, and my cam is a 272 crane cam, which is a truck came so low end to mid range torque is good,

http://www.cranecams.com/product/cart.php?m=product_detail&p=23806

theres my cam, and 3.91s with 26 inch tires seems a good idea, and ill only be using it as a cruiser.