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Old 12-15-2009, 04:12 AM
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1986 Grand Prix Tranny Upgrade

Im wanting to put a 383 stroker in my 86 grand prix. Currently has a 305 what tranny should I run with?

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Old 12-15-2009, 05:04 AM
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The car should have a 700r4 you could have it built to handle the power of the engine. Or you could use a 4L80E.
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Old 12-15-2009, 05:11 AM
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None of the G-body cars came with a 700R4. The car should have a 200R4 in it from the factory, and it would be worth rebuilding if you want to keep the overdrive.

Simplest, cheapest way out would be a Th-350, but you won't have OD.
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Old 12-15-2009, 05:26 AM
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Would a TH350 hold the power ok? Im hopin to push about 450hp.
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Old 12-15-2009, 05:28 AM
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Quote:
Originally Posted by GrandPrix8686
Would a TH350 hold the power ok? Im hopin to push about 450hp.
Yes, not a problem at all if properly put together.
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Old 12-15-2009, 05:31 AM
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And that would bolt up to the crossmember thats in the car
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Old 12-15-2009, 08:11 AM
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I guess I most of push 7 instead of 2. No if you go with a th350 you will need a crossmember from a car with 3speed auto. One from any G body car 78-88 would work. You would more likely to find one in a early 80's car. Summit sells new one they are double notched for duel exhaust. If you plan on driving it on a regular basis than OD is the way to go. If it's just a toy th350 would be the way to go. My 81 Gran Prix I built 16 years ago had a stroker sbc and th350 2,200 stall, with 3.73 gears in the rear end. It ran around 3000rpm at 55mph if I still had it. I would change it out to an Over Drive, but that's just me. By the way on upgrading the rear end. 8.5 rear end out of a Grand National or 442 from the 80's is best this kind of build, but they are getting harder to find. You can get parts from an S-10 rear end the gears, carrier, and posi unit. That what I had in my 81.
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Old 12-15-2009, 08:24 PM
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Quote:
Originally Posted by GrandPrix8686
And that would bolt up to the crossmember thats in the car
Yes, but you will have to move it forward on the frame. The stock crossmember won't allow you to easily run dual exhaust because it has only one clearance hump for the exhaust pipe. You can buy aftermarket, or if you can find a crossmember from an 64-72 Chevelle it can be easily slightly modified to fit the car and has two humps in it for exhaust pipe clearance.

The TH-350( short passenger car version) and the 200R4 take the same driveshaft. Slip yoke is also the same.
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Old 12-15-2009, 09:42 PM
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You can't use the same crossmember if you change it to a th350. Their is no place for you to move it up on the frame. They made two different crossmembers for this car one for a 3 speed auto, and one for a 4 speed auto. You have to have one or the other. You can't use one for both like you can with the A-body cars, but the right one's are easy to find in junk yards. If you plan on running 3 inch exhaust you would be better of getting one from summit.
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Old 12-15-2009, 09:53 PM
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You may be correct 70455, I only moved the crossmember back from the 350C position to the 200R4/TH-400 position and not vice versa. I have heard of just adding to the frame ledge with a welded extension piece to allow moving the crossmember forward, but havn't seen it personally. I have done the early 64-72 Chevelle crossmember swap, it is real easy and obvious when you have it in hand under the car, and cheap if you can find one on a yard.
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Old 12-16-2009, 05:05 AM
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Yeah I have a 70 442 it's like the Chevelle you just put the crossmember where you need it. On the G-body cars they have two different crossmembers. That's why I used my 81 Grand Prix I built as an example because I built a car just like what wants to build. It was a fun car some times wish I didn't sell it. The guy that bought it couldn't handle it. It only lasted about two months before he crashed it.
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