1982 Olds Cutlass Supreme Posi Rearend Swap

[olds307 and 403]

Exactly, I have had a few Olds 350 and a 403. None were even 300 hp except maybe this one. The 403 broke a Powertrax no slip at the track with slicks, doubt it had more than 250 hp. The maybe 200hp 350 exploded the stock soft spider gears, blew through girdle cover just flooring it on the street. The 9.4 in the 1/8 mile 9.5 to 1 Olds 350 with the Yukon replacement open spider gears look perfect after multiple track runs with slicks. No doubt a much better forged steel and under $100.

 

[rcs0296]

Yeah, make sure about the studs. Not hard to change em. Keep in mind, there are 2 carriers the 7.5s used. The series 2 and series 3. iirc the series 3 is 3.08 and numerically higher (3.23, 3.73, etc) and series 2 is 2.14, 2.29, 2.41, etc. You could just buy an aftermarket posi setup and refresh the rear end. I'd poke around on craigslist. I've seen a lot of 3.73 monte rears (7.625 rear end) on the net for sale. As said above a GN/442 would drop right in (GNs had 3.42/3.73s, 442s had 3.73, posi was optional on both. The thought of a one wheel peel GN makes me giggle.) with a 1 inch SHORTER driveshaft. The 7.5 d/s are spindly and would probably rip in half from your 350. If it's got 400hp like you say, it's got damn near 500ftlbs.

A stock v8 driveshaft should handle 400 hp,mine has for 20+ years

 

[MrSony]

A stock v8 driveshaft should handle 400 hp,mine has for 20+ years

Also depends on if one is using slicks, or has a manual trans. But generally speaking, yes.

 

[454GrandPrix]

You could also do a Ford 8.8 out of a foxbody mustang with a trick chassis swap kit

That's what I did.

You can pick ... a Detroit Trutrac

I will give this limited slip diff a hearty endorsement. I've got one in my 8.8, and it works extremely well... so much so that I can only go WOT when the car and the wheels are pointed dead ahead, and even then I need both hands on the wheel to try and keep the car going in my intended direction while both rear tires spin. It's borderline dangerous. I like it that way.

What gear ratio should I look For? ... Not looking to rev 4000rpms at 60mph.

Go find an online gear ratio calculator, enter your tire size and transmission gear ratios, then plug in various axle ratios until you find the one that puts your car where you want it to be. In fact, here is a simple one that will tell you exactly what you want to know:

https://www.ringpinion.com/calculators/Calc_RPM.aspx

Scroll down to the Transmission Ratio RPM section. Input the four values across the top line, then click Solve. It will tell you the resulting engine rpm at the road speed you entered. Don't like that rpm? Try a different R&P ratio and see how much it changes. Easy.

Be advised: it is easy to "armchair quarterback" your way into something that doesn't quite satisfy you. When I built my car, I thought the shallow overdrive in my 4L80E (it's only a 0.75 ratio) would make me want a slightly taller R&P to keep highway revs down... so I initially installed my 8.8 axle with a 3.08 axle ratio. On paper, that was exactly what I thought I wanted. Once I started driving the car, real-world experience left me feeling like the revs were a little lower than I could handle... so after only a few months, I opened the diff and changed out that R&P for a 3.55 set instead. While it does rev a couple hundred rpm higher on the freeway, it made the car much more lively and fun in the lower gears... and I am now a lot happier with it.

$.02

 

[olds307 and 403]

What did you do to the 4L80E to fit it and what internal mods? I want to go that way in my 70 Cutlass or TKO 5 spd which is definitely dollars to do.

 

[olds307 and 403]

Also depends on if one is using slicks, or has a manual trans. But generally speaking, yes.

The 8.5" drive shaft is beefier without a doubt. I had both the 7.5" G body and my A body 8.5" Type shaft, side by side. Ask a girl if she wants a needle dick or a big fat one.

 

[lilbowtie]

Driveshaft critical RPM is what you need to be looking at.

 

[454GrandPrix]

What did you do to the 4L80E to fit it and what internal mods?

This question comes up just often enough that I think I'll go make a dedicated thread about it. That way, it will be easier for people to search and find some answers.

 

[Rocket Powered]

I don' t use slicks on the cutlass. I built it for a street beast. I have posi to get is what I have let to do. Then I will throw my $ to a s10 for drag racing. Chevy...parts are very cheap compared to an olds...

I did find a 1981 pontiac bonneville with a posi rearend. Looks just like mine. Will this bolt up?

 

[Kwik_Cutty88]

I don' t use slicks on the cutlass. I built it for a street beast. I have posi to get is what I have let to do. Then I will throw my $ to a s10 for drag racing. Chevy...parts are very cheap compared to an olds...

I did find a 1981 pontiac bonneville with a posi rearend. Looks just like mine. Will this bolt up?

If you're looking to swap the entire housing into your car, no a 1981 Bonneville is a B Body. A 1982-1986 Bonneville would work to swap the complete housing, but most of them came with open rears.

If you're just looking to only swap the center section out of that 1981 Bonneville, and it does indeed have a GM 7.5" (I think some low option b body's came with a 7.5", but don't quote me on that) then you'll need to verify the spline count, and carrier series to make sure it'll work with what you're trying to do.