1982 Olds Cutlass Supreme Posi Rearend Swap

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Welcome to the forum.
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what tires do you want to run? what trans? Th350? Manual? Th200r4? Gotta keep all that in mind with gears. Plus you want your highway rpm higher than the stall speed for fuel economy's sake.
 
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With 3.42 gears, stock on the early 3spd Monte SS and stock height tires you will run around 3000 rpm at 60 mph. A 3.23 or 3.08 gear might be more friendly on the highway but less launch. Your motor must have heavily ported big valve heads plus high compression and a big duration/lift cam to hit 400 hp, along with full length headers, X pipe and 2.5"+ duals. My Olds 350 is probably 300 hp and 350+ ft/lbs.
 
With desktop dyno it REALLY helps to have the flow numbers @ certain lifts .100, .200, etc. so it can get an accurate number.
 
If you are running the stock 71 heads, unported you will not be hitting 200 cfm on the intake. I believe the flow 185-190 at peak on the intake and 150-160 on the exhaust side. I am probably just over 200 cfm on the intake and maybe just over the stock exhaust numbers. This is with a 2.05" intake valve and the stock 1.56 intake valves. They did use a cutter to open the bowls under the valves. Unless this and blending was done with a 2" or 2.07" intake and 1.625" exhaust valve, your heads will flow poorly. You woild need flat tops and big cam in the 230 duration range. My 350 burns the one tire with 2.78 gears and the 2200-2500 converter which flashed at 2300 stall until the 2004R was run low on fluid. With the TH350 and the stock 1800 stall, less impressive. My motor is right at 9 to 1 compression and has 214/214 .472/.472 cam, 300hp might be dreaming but 350 ft/lbs is probably close. A guy rear wheel dynoed a 9.5 to 1 Olds 350 with a little more cam than mine. He was disappointed. It worked to about 260 hp and 365 ft/lbs of torque. The Olds 350 has a much better torque curve then brand "C". Don't mistake torque for horsepower.
 
If you are running the stock 71 heads, unported you will not be hitting 200 cfm on the intake. I believe the flow 185-190 at peak on the intake and 150-160 on the exhaust side. I am probably just over 200 cfm on the intake and maybe just over the stock exhaust numbers. This is with a 2.05" intake valve and the stock 1.56 intake valves. They did use a cutter to open the bowls under the valves. Unless this and blending was done with a 2" or 2.07" intake and 1.625" exhaust valve, your heads will flow poorly. You woild need flat tops and big cam in the 230 duration range. My 350 burns the one tire with 2.78 gears and the 2200-2500 converter which flashed at 2300 stall until the 2004R was run low on fluid. With the TH350 and the stock 1800 stall, less impressive. My motor is right at 9 to 1 compression and has 214/214 .472/.472 cam, 300hp might be dreaming but 350 ft/lbs is probably close. A guy rear wheel dynoed a 9.5 to 1 Olds 350 with a little more cam than mine. He was disappointed. It worked to about 265 hp and 350 ft/lbs of torque. The Olds 350 has a much better torque curve then brand "C". Don't mistake torque for horsepower.
 
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With over 400 HP (11 sec car) you might want to consider a better rear.
Agree. If you have that much and get traction, any 7.5 or 7 5/8" rear is on borrowed time.
 
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