Putting a T56 Behind a Poncho 400/455

[Vetty]

Has anyone on this forum attempted this swap or conversion with a modern T56 to a Pontiac 400/455 engine?I know Takid455 is doing his as we speak but im just wondering if there is anyone else out there that has done this and has detailed pics and or video. Looking to put a T56 behind a 400/455 in a second gen trans am in the future.

Thanks,
Matt

[matthimself456]

If I remember right there are three basic options here. First, and expensive, is that modular bellhousing by McLeod. Second is use an LS1 style T56 with its original application bellhousing and clutch with one of those $40 Chevy to BOP bellhousing adapters from Jegs meant for automatics. This requires some grinding as the Pontiac starter is on the opposite side. I think it also requires a spacer between the crank and flywheel to make up the thickness of the bellhousing adaptor. The third option is really wild and done by a fellow in Sweden who hangs out here I think. He wanted to do this before anyone else thought of it and could only come up with an LT1 transmission (might have even been before LSX days). He cut a traditional Pontiac bellhousing in half along with the T56 bellhousing and welded the two together. Obviously that one takes a great deal of skill and labor but he made it work. His website is propontiac.com I think.

Personally I would look into option 2. Check out the Performance Years Forum and do a search there. It has been done and it can even be done affordably. Hope this helps.

[chicane67]

ATS at one time made an adapter plate... just for this.

Or... McLeod makes a complete scatter shield.

[BulldawgMusclecars]

There is another option; someone in High Performance Pontiac used an aftermarket (Chevy) style T56 with a standard lakewood 4 speed style bellhousing and mechanical clutch linkage, after redrilling the bellhousing. I'll try to find the article.

[Takid455]

"He cut a traditional Pontiac bellhousing in half along with the T56 bellhousing and welded the two together" - I saw that and while I realize it was a lot of work, I prize my feet too much to install an aluminum bellhouse in a high power application.

Do to design charateristics, I have found that the LT1 front plate is a better choice. do not use the ls7 style clutch as the bolt patterns to the flywheel are different. a modified lakewood or stock bellhouse from a pontiac works well. the modification is relatively simple, locating the points to do the modification take time and are very percise to line the inputshaft up with pilot bearing. as far as fitment is concerned, you can use a stock gm hydraulic TO bearing. I have not gotten the opportunity to see if this works on the street.

[PT Goat]

I looked into a T56 for my GTO and decided against it. Too few advantages over the TKO to justify the extra cost/hassle. I just didn't think the extra gear was worth it. How often would I need a .50 OD anyway?

[matthimself456]

You never NEED 0.50 OD but cruising at 75 mph turning 1500rpm and getting 25mpg sure is nice. Consensus seems to be carbed motors really dont like it but my dad's formula with the LT1 loves running at those low low rpms. For a lot of folks the t56 can be done a lot cheaper than the aftermarket boxes, too.

[SDMAN]

Im using a T-56 on my 70 GTO project, but it wont be driveable until next spring. Have all the parts. Went with the McLeod bell, hydraulic T/O bearing and aluminum street twin clutch.

I can agree with the comment about the stock factory gearsets with the ridiculously low OD gears. If you have any kind of H/P camshaft, the motor wont like cruising at 1500 RPM very much. My last trans was a TKO-600 with the .64 OD ratio. I was using a very mild solid street roller in the 464, and after trying 3.55, 3.70 and finally 3.89, I settled on the 3.89.

The new T-56 has aftermarket ratio's in it for all 6 gears. Final OD of the set I chose is .75. The rear gear is a 3.70.