Rear differential efficiency
 

As far as GM's go, has anyone done any A-B-A testing, or a real good A-B of which is more efficient, the 10 bolt (8.5) or the 12 bolt. Looking in another area, for some gains for future.

Thanks !
Kenny





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Re: Rear differential efficiency
 

Kenny, I have no test results but offer these thoughts. The 8.5 will be at least a few pounds lighter and has proven to be completely acceptable in even very high powered cars.

From the view point of mechanical losses, I do not think the difference will be enough to measure, I think either choice will give good results.

Is this for your stocker? If so, what are your running now?

Re: Rear differential efficiency
 

Yes, thanks Larry. I was thinking of trying to make it as effiecient as it could be. I have the 10 bolt in mine now, and was wondering if the 12 bolt was worth a swap, as far as reducing the losses wherever they are.

Re: Rear differential efficiency
 

I think you have the best choice. Going to a 12 bolt would not gain anything, in fact, I think you would loose ground because if nothing else, the added weight.

Re: Rear differential efficiency
 

Once you put a spool,good axles, wheel studs, the proper bearing kit and steel web caps in the 8.5" 10 bolt,(which you do to any race car rear end,anyway),it probably has 90-95% the strength of a 12 bolt. I don't think the weight is more than 5 pounds difference, but cost and availability is a real factor here. I wouldn't pull out a 12 bolt in any of my cars for a 10 bolt because they are there already,but if I had the 8.5" 10 bolt, I would go no further in my search. One advantage to the 12 bolt is the availability of gear ratios is larger.

Re: Rear differential efficiency
 

i just switched from a 8.5 ten bolt to a 12 bolt and with similar
components and same gear ratio i think the
10 bolt was .03-.05 quicker, both are set up the same way.

Re: Rear differential efficiency
 

Thank you all. I was wondering if anyone had done that swap, and found any real difference. I have an 8.5 10 in it now, and will likely do a new R&P this winter.