need posi info help on 1971 lemans - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 02-25-2016, 06:04 AM Thread Starter
 
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need posi info help on 1971 lemans

looking to purchase a posi for a 1971 Lemans 10 bolt,i assume its a 8.2 im looking at this for the posi, is it a correct one
Search Results for 5420113 - Free Shipping on Orders Over $99 at Summit Racing

also it shows for 3.36 and up application, is 3.36 this a good ratio for street application, first i was thinking 3.23 would be best but cant find a auburn rated for 3.23, also what other parts will i need for the install, Bearings? i was looking at richmont ring and pinion, Any help would be much appreciated
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post #2 of 3 (permalink) Old 02-25-2016, 06:33 AM Thread Starter
 
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or is this one correct
Auburn Gear High Performance Series Differentials 5420114 - Free Shipping on Orders Over $99 at Summit Racing

also need help finding the correct ring and pinion ,

Last edited by crxnug; 02-25-2016 at 06:43 AM.
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post #3 of 3 (permalink) Old 02-25-2016, 09:20 AM
 
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The first carrier you have listed is the std performance Auburn posi for low ratio 8.2 Pontiac gears. The latter is the mid ratio carrier (2.93-3.08-3.23).

What engine and trans was factory installed in your LeMans? If the car was an automatic 350 car with AC, most likely it will have 2.78's. If it came with a 400 4bbl and turbo 400, the factory rear will have 3.23's. 3.23's are about as low a ratio that I like to use in a rearend build in a car that sees highway driving. With taller 15" rear tires, 3.23's can be tolerable with a 1-1 top gear transmission. If shorter tire/wheel combo is part of the package, then 3.08's are as low (high numerically) as I like to go.

A few cruise rpm examples from own Pontiacs
-27.625" tall 265/60's on 8" rear wheels w/ 3.08's, 70 mph=2650 rpm
-shorter 255/60's on same above car w 3.08's, 70 mph near 2750
the 265/60's lasted nearly 3 times as long on the rear of that T/A, than the shorter 255's, unfortunately, can't buy the 265's anymore.

-26.375" tall G70/14's on 6" wheels w/ 3.55's, 70mph=3200 rpm
-26.375" tall G70/14's on 6" wheels w/3.73's, 70 mph= 3350
with 3.73's, will trap @ near 5400 rpm @ 110-111 mph.

Building performance GM rears, I typically use the 8.5 A body rear due to its superior strength, and the wide variety of gearsets, posis, spools that are available. Occasionally, build the 12 bolt. Can order new gear sets for both type rears in 3.08's, but have built both with many nice used gear sets. For the Pontiac 8.2, have built many rears with nice used 2.93's, 3.23's, 3.36's. Do have at least one 3.23 gear set, doubt I have any 3.08's. For many years, the most popular ratio I built in 8.5 Abody rears was the 3.42, few of those A bodys were taken on road trips, most were built for street/occasional strip use. Hope this helps.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO General Discussion

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