Looking at changing to a 455 in my '72 GS convertible. Right now I'm looking at a stock '74 smog motor. I'd throw an intake and headers on it but that's probably it. Can I stay with my TH350 if I build it up a little (it needs a new rebuild anyway)? If I go TH 400 do I use long or short shaft? What about 700 or 200? Just looking for ability to handle the tq/hp reliably...Your thoughts please. Thanks!
A TH350 will handle a 74 455 without a problem. It sounds like you will be fine with what you have and a freshening up like you plan to do. As with a 400, you want a short shaft tranny. And you need to get the yoke for a 400 as well, as it is different from a 350. If you are looking at O/D's, I understand that the 200 is the best route to take. It has the BOP bolt pattern, a 350 yoke fits it and tail housing length is the same, so you use the same drive shaft. I have heard that the crossmember and mounting are the same as well, you just need a special mount on the tranny. I am not too sure on the 700's for thier usability. Mike
You can get by with a 350, especially if you aren't driving WFO very much. A 350 can be built to handle significant horsepower if you spend enough. The 400 is more suitable in stock form, and BOP-case 400's are cheap and plentiful, especially the long shaft versions. A core 400 long shaft can be had for about $50-$75 around here, and usable used ones start at $100 or even less if you get lucky. Of course, you'll spend more for a short shaft, or for one that has a recent rebuild, or comes with a warranty. I have no experience with 200s and 700s behind big blocks. I guess the aftermarket support is there to make them tough enough, but you'll spend crazy amounts of money doing it. The extra gear is a genuine good thing, and maybe that makes it worth the money. In any event, the 700 is a Chevy-case only deal, so you'd have to have an adaptor to connect it to your engine.
i just did this swap in my 71 skylark. the th350 slipped on the 2-3 shift pretty bad. the trans had 113,000 miles. i put a shift kit in and so far so good. i've done about 10 passes on the drag strip and alot of driving with lots of abuse and its holding up good.
I'm running the 200R4 behing the 71 455 in my 65 Skylark. It was there when I got the car, so don't how difficult it was to install. I do know it was rebuilt with HD parts prior to installation at a cost of around $1200, (core, rebuild and install), and has maybe 4K miles on it. Seems to work great so far and mileage with the OD is about 17-18. Not too bad for a 455. Keith
When making the swap from a 350/TH350 to a 455/TH400 is it necessary to change the transmission cross member? I understand the 350 cross member and 400 cross member have different part numbers?? Thanks Harvey
They have different part numbers because the TH400 x-mbr has an oblong hole for the e-brake cable to pass through. The 350 versions, the cable goes over the x-mbr. As for TH400, get one from a 73-77 Grand Prix. All of those models had the short-shaft 400 from the factory. Here is the article I wrote on this swap. http://www.buickperformance.com/conversi.htm
The Turbo 2004r trans is a much stronger trans than the 700. My 87 GN's stock unrebuilt trans is putting up with over 400 hp. and 524 ft.lbs. at the rear wheels. The car weighs 3560lbs. Mark
