Adapting T-56 to 60*V6

[caffeine]

So I'm going to start hopefully soon on a 3500/89 Firebird project and I'd like to use a T56. I've done some research and I think I have decent plan for adapting the transmission to the 3500. I'd like some input on whether what I'm planning will or will not work. The V8-oriented gearing of the T56 will be compensated with 4.11 rear gears or maybe even steeper if necessary. I currently have a 9-bolt with 4.11s installed and the gearing felt really nice last time I drove it.

First, I'm starting with an LT1 T56, which right away causes an issue because of the pull-style clutch it uses (needs a special pressure plate). To overcome this, I've ordered a McLeod hydraulic throwout bearing to convert it to a push-style system.

Next, there's the Speedway Motors adapter for the TH-350. I'm thinking this can work with the T56 as well, so I've ordered one of these. Installing it should be the same as how Mars did on his Camaro.

To compensate for the LT1 T56's short input shaft, my plan is to use a 3.4L Camaro flywheel bolted overtop of a 3500 flexplate, also compensating for the adapter plate thickness and allowing the FWD starter to still be used. I'm expecting the bellhousing to need clearancing for the starter but I'm not sure how much.

Now when it comes to clutches I'm thinking a 6-puck is the way to go possibly from clutchnet but the clutch they have listed for the 3.4 is more expensive than the 2.8/3.1 and the only difference as far as I can tell is the spines on the clutch disc. Am I better off just ordering a disc and using a stock pressure plate or will I need a really agressive pressure plate (up to 450hp hopefully)? I am trying to keep the cost semi-low/reasonable .

Does the 3.4 flywheel have the same pressure plate bolt pattern as the FWD flywheels? I know it is thicker and larger in diameter.

[robertisaar]

i would think the flywheels use the same pattern.

[caffeine]

So I've started to progress with this; picked up an LX9 from an 06 G6 with either 50,000 miles or kms.


And I picked up a flywheel from a 95 Firebird 3.4L. It looks like bolting to the auto flex plate will not work as I will need shims between the two, and the Firebird flywheel's ring gear will interfere with the starter. I think, however, that with a flywheel shim, the 3.4L flywheel will be thick enough to work with the LT1 T56. My T56 is almost out of the car and my trans adapter should be here next week.

My question is, however, since the 3.4L flywheel has a slightly larger diameter, can I just shim the FWD starter the difference in radius between the flywheel and the flexplate to use it? They seem to have a very similar distance between teeth but the flywheel does have IIRC 6 more teeth than the flexplate.

Here are some pics:
Flexplate shown over flywheel


Flywheel thickness:

[Mars]

^ I'm using a RWD flexplate (2.8 camaro 700R4) on my FWD 3500 WITH a starter shim, I forget how thick it is, but I tried it with washers, found the size that worked, then I got a piece machined as a shim. It's pretty thick though, like around 9/16" if memory serves.

[caffeine]

^ I'm using a RWD flexplate (2.8 camaro 700R4) on my FWD 3500 WITH a starter shim, I forget how thick it is, but I tried it with washers, found the size that worked, then I got a piece machined as a shim. It's pretty thick though, like around 9/16" if memory serves.

Hey since you're using the adapter plate I was wondering something about the pilot bushing. The adapter comes with some sort of crank adapter for a th350 torque converter and I was wondering if that adapter would fit a standard t56 pilot bearing or not.

[caffeine]

If I can't use the t56 bushing I think the 3.4L T5 bushing might be the right size anyway

[caffeine]

Ok time for an update. Trans adapter arrived today so I pulled the old engine out of the Firebird with the T56 to start the test-fitting process.




It looks like the LT1 flywheel protrudes from the block face an extra 15mm compared to the 3.4L flywheel from the adapter face:




If I could bolt the flywheel over a FWD flexplate it appears it would make up the majority of the difference:


And the worn area on the trans input shaft appears to be just over 11mm from the tip of the splines:


Did some clearancing to the bellhousing to make room for bolting on the adapter plate, still need to grind down the LX9's dowel pins:

[caffeine]

PS: anyone have an old garbage 3.4L camaro clutch/pressure plate they want to donate that I could use to test fitment when my HTOB arrives?

[TGP37]

A flex plate spacer may help with the flywheel difference. I have a spare one after swapping my auto to manual, I could measure the dimensions for you if you want.

[caffeine]

What do you mean by flex plate spacer? If you mean flex plate then I already have one. I just also ordered a bunch of flywheel shims from rock auto.

[TGP37]

What do you mean by flex plate spacer? If you mean flex plate then I already have one. I just also ordered a bunch of flywheel shims from rock auto.

It was between the flex plate and the crank, looks like an oversized washer with holes for the 6 bolts. I think it is roughly 1/8" or 3/16" thick, somewhere in that range.

[caffeine]

Hmm maybe I already have one? I bought my engine with the 3500 flex plate attached; maybe it's just rusted on mine or something. In any case, I have just over 8mm worth of shims coming probably tomorrow so we'll see where that gets me. If I shim out the flywheel too much without using the flex plate as a spacer then the starter probably won't be able to engage anymore.

[caffeine]

Ok I got shims in yesterday; I'm not sure how far out I feel comfortable shimming but I won't verify any setup works until getting a clutch. Worst case scenario I have to buy an LS1 input shaft which is longer by about an inch. A new input shaft is $200 so I'd rather not go that route. I shouldn't need the ls1 mid-plate since I already have a HTOB. If I did end up getting the ls1 input shaft I doubt I would need an extended pilot bushing and a regular t5 pilot bushing should be the perfect size

Anyway, enough ranting

[caffeine]

Pic of the HTOB on the trans

[caffeine]

In other news it looks like the bellhousing won't need any grinding to clear the starter: