Hi speed aftermarket rear end?
 

Went this AM to help a friend who had just removed engine and transmission from a '31 pickup. We plan to dive into the rear axle assembly tomorrow. As we discussed possibly changing the ring and pinion for a higher ratio, we decided to try to determine what rear end ratio is in the truck. So, we jacked up the truck. A complete 360 degree revolution of the rear wheel resulted in slightly less than 2 revolutions of the drive shaft. Seemed odd, so we did it again. What do we have here?

Been on meds lately, so I am reluctant to do the math. Seems like a really high rear end ratio, or am I still in a pharmaceutical fog?

Re: Hi speed aftermarket rear end?
 

When you hold one wheel stationary don't you double the ratio through the differential? So it sounds like you have the standard 3.78:1. 3.78/2 = 1.89 which is about what you say you measured.

Re: Hi speed aftermarket rear end?
 

Yes it is doubled when turned one completed revolution with other wheel locked from moving.

Re: Hi speed aftermarket rear end?
 

Yep, with one wheel turning, it will turn twice as fast, so you need to make two revolutions of the tire and count the revs of the engine. Or, an easier way is to hand crank the engine 3.78 turns and see if the rear tire makes exactly two turns.

Re: Hi speed aftermarket rear end?
 

A 3.78 ratio is a quite decent ALL AROUND RATIO. I, personally, would not change it, like, how fast do we need to go?
Bill W.

Re: Hi speed aftermarket rear end?
 

My experiences is a Model-A with a high-speed Ring & Pinion greatly enhances the drivability. At minimum, we typically install a 3.54 ratio and often install the 3.27 ratio. These two ratios are good for another 4-7 MPH at cruising speed. While that does not sound like much, it takes an engine that likes 45 mph and turns it into roughly a 50 mph vehicle. Often times this is just what is needed to keep from holding-up traffic.

Re: Hi speed aftermarket rear end?
 

GOOD point you made, Brent,
"Maybe" these inputs will help Del consider what is the best for HIS NEEDS.
3:78's are fine for ME, as I'll be mostly in Big City driving.
Bill W.

Re: Hi speed aftermarket rear end?
 

3.78 is fine by me as well. 80% of my driving is city driving as well. For the long haul open highway tours, I just slip it into overdrive, sit back and let the engine loaf!

Re: Hi speed aftermarket rear end?
 

I think for me more importantly 354 gears would take a car that likes to run 45MPH and reduce stress on the engine by reducing rpm's. The added benefit is the extra 4-7 when you need it.

Re: Hi speed aftermarket rear end?
 

Thanks guys! I completely forgot about the X2 if rotating the one wheel. 3.78 is what I would expect to find. I installed the 3:54 in my truck a year ago. It did make things a little less effort at 45-50 MPH. If I had it over, I might have opted for the 3:27, but that is some serious $. Thanks again!

Re: Hi speed aftermarket rear end?
 

I put 3:54's in Lucy ( Tudor) with an HC head, it does relieve the R's but would go with 3:27's next time around. I'm not looking to blow any axle keys out of the hole

Re: Hi speed aftermarket rear end?
 

I put 3:27 gears in my 31 Tudor back in 2001 and turned my car into a great driving experience. They advertise that the gear will give you 10 mph extra speed. Wrong it will be 7 mph but 7 extra mph is really great in a bone stock A. Through the years have added other up grades, check my avatar info. Have fun modelAtony tony white Lafayette, LA

Re: Hi speed aftermarket rear end?
 

I put 3.27 ring and pinion in my friend's pickup, and would also like to build a 3.27 rear end for my car.