Gear ratio?

[spectrumad]

Hey all,

I have a 1971 Lemans Sport Convertible. Rebuilt original 350, nothing radical. Rebuilt original 350 tans. The original 10 bolt 2.56 open rear end has got to go!

This car will mainly be driven in town with the occasional backroad highway trip. No racing, just cruising.... But who doesn't want to smash throttle and let loose now and then?!

I am planning to replace the carrier with an Eaton posi unit. I am thinking in the realm of 3.23 - 3.55 for gears. Anyone have any input? Am I simply splitting hairs at this point and just shoot for the middle with 3.42? Or am I off in my thinking and should I go another route?

Thanks!

 

[melsg5]

Anything you do to get away from the 2.56, even 3.23 will be an improvement.
Without knowing your tire size a 3.55 will be doing about 2,650 rpm at 60 mph.
I went from 3.08 to 3.55 and had a significant improvement in seat of the pants acceleration.
Here is a calculator.

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.

spicerparts.com

 

[spectrumad]

I am running 245/50-17 rears. 26.6 diameter. You are right. ANYTHING will help a ton.

 

[cammerjeff]

If you do not plan on doing any long highway trips 3.55's would be my choice. If you do plan on taking longer trips say 2 hours or more I would stick with 3.23's Both are common gear ratios. I forget the 2 series carrier cut off but I think it is 3.23's would work with your current carrier. Anything more will require a 3 series carrier. or a spacer plate to use with a 2 series carrier.

I know you planning to replace the carrier also, just something else to think about, sometimes you can find a deal on a 2 series posi carrier, add the 3.55's and a spacer plate and save around $100. At your power level I would be comfortable running a spacer and longer bolts below 500hp and no sticky tires.

Good luck, but be prepared for a price shock as the BOP 8.2 axles are about the most expensive axles design to buy parts for.

______________________________

 

[spectrumad]

I will likely drop the entire rearend and take it to be rebuilt. Luckily, I live only about 10 miles from Quick Performance in Ames, IA. They do builds that take much more abuse than mine ever will!