Automatic Transaxle Options (Page 1/2)
Reborn756 MAR 17, 12:38 PM
Howdy folks! I'm going to keep this one short and sweet: I'm looking for the absolute strongest automatic transaxle that will:

A: fit in an 88 Formula
B: Bolt up to an SBC and still fit in the Fiero.

AFR (the head company) is telling me to expect 600HP at the crank out of this engine. I need something that will hold to that kind of power at a max of 6500RPM. Not just looking for budget options, need something that's going to handle the abuse.

Thanks in advance for any advice you have!

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- Darryl

FieroJimmy MAR 17, 05:33 PM
If you mean bolting to an SBC without adapters, there are none to my knowledge.

So, assuming you are open to using an adapter plate: The TH425 would be the strongest. That will mean custom motor and trans mounts, and custom axles. It is a longitudinal FWD transaxle based on the TH400, they have been used in several big block Fieros. You will lose some or all of your trunk.

If you want to stick with a transverse mount engine, the 4T80E would be the strongest. That will need an adapter, custom mounts, custom axles (I believe, I haven't really looked into a 4T80 swap. But stock axles certainly won't work.), and a trans controller (either stand alone, or integrated with your ECM). I know that on the N*/4T80E swaps the cradle needs to be modified, but I don't recall if that is for the trans or the engine.

I haven't paid much attention to the newer 6+ speed transaxles from GM, so I'm not sure exactly where they stack up against the 80E as far as strength.
Reborn756 MAR 17, 05:51 PM
Thanks for the response Jimmy! Definitely want to stay transverse. 4T80 was one of the most logical conclusions to me, however the concern of whether or not it'll hold is definitely a strong one!
MichiganReefer MAR 17, 06:09 PM
I wonder if the 9T65 would work? Those are mated to the 3.6L v6 which is rated for 310HP and 268 lb*ft. Barely larger and hardly heavier than the 6TXX transmissions.
fieroguru MAR 17, 06:14 PM
The 4T80 is what is most commonly used with the turbo LS4s pushing 800+hp. You will need an adapter plate to run it as well as a transmission controller.
Reborn756 MAR 17, 10:52 PM
That's what I like to hear FieroGuru! Stock 4t80s or are there quality rebuild kits available?

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- Darryl

sanderson231 MAR 18, 11:24 AM
A lot of the high HP 3800 supercharged builds use a built 4T65HD which is lighter than the 4T80E.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

Reborn756 MAR 18, 11:29 AM
Hey Sanderson! I did a ton of reading on the 4t65s last night. I also came to the same conclusion but Triple Edge Performance informed me this morning that the parts are no longer available to build them that strong. Any idea what parts are needed? I read that a 1" chain is needed and found a company reproducing them. Pricey, but with the money I'm putting into this engine, I'm not going to cheap out on the transaxle.

Lighter is better for me. The entire engine build is designed from the block up to be as lightweight as possible. Hoping for an engine that comes in at about the same weight as the all cast OEM 2.8L with over 4X the crank HP
tampalinc MAR 18, 08:41 PM

quote
Originally posted by Reborn756:

Hey Sanderson! I did a ton of reading on the 4t65s last night. I also came to the same conclusion but Triple Edge Performance informed me this morning that the parts are no longer available to build them that strong. Any idea what parts are needed? I read that a 1" chain is needed and found a company reproducing them. Pricey, but with the money I'm putting into this engine, I'm not going to cheap out on the transaxle.

Lighter is better for me. The entire engine build is designed from the block up to be as lightweight as possible. Hoping for an engine that comes in at about the same weight as the all cast OEM 2.8L with over 4X the crank HP



Let me see if I can find the parts list from when Triple Edge Performance built my trans.
4T80would be a good choice if you can't find the parts for the 4T65E
Reborn756 MAR 18, 08:46 PM
Thanks Tampa! Would prefer 4t65 to meet my weight goals, even if it costs more than a 4T80 setup. 4t65e-HD is only 40 lbs more than the TH125C when both have their converters from some rough numbers I saw. I can easily make up that 40LB weight increase by moving the battery to the front and making some modifications to the exhaust system, along with the weight savings I should see with the new engine.