Join Date: Jan 2015
Location: Injun Territory, 'Merica!
Mentioned: 0 Post(s)
Tagged: 1 Thread(s)
Quoted: 121 Post(s)
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.