Hey guys new to the forum so bare with me. So I have a question regarding the 4t65eHD. I currently own an 84/88 Pontiac Fiero. I’ve swapped in a gen 1 SBC 383 stroker with a 76mm precision turbo mates to a 4t6eHD. The car on low boost will be around 700hp. The transmission was built by Dave at TEP with all the upgrades he provides. It has the 1” GMR chain and their 1000hp input shaft. Is there anything else you high hp guys are doing with this tranny to make it stronger? I already have upwards of 6000$ into the transmission alone and I’m wondering if swapping to a 4t80 is better/stronger?

The 4T80 is an odd transmission. They were good, but odd . . . in the sense that few know anything about them let alone building them up. The 4T6x, on the other hand, has been getting built-up for ages for the GTP and GS crowd. That having been said . . .

That'* a lot of torque and horsepower for a 4T6x . Especially torque.

Was it built to handle this engine?

Did Dave release it to you with some kind or warranty?

Stronger than a specialist building it for 1,000HP? We probably won't have any recommendations. If we do, I'm sure someone will chime in with "Well actually CathedralCub, I do have a recommendation or two . . . "

Ummm . . . $6,000.00 deep and thinking of swapping already?

The 4T6x has a significant aftermarket and knowledge base. The 4T80 does not. I'm sure that if you want to pay for someone to learn their way up to being the world'* only 4T80 Supreme Wizard Specialist and supply that person with a stack of cores and a blank check for parts, you could probably get a 4T80 to do better, but this is Fantasyland levels of money for probably little improvement.

The biggest question that I have is: What tires are you running on this combination? A Fiero is a pretty light car. Even with 700HP and/or I'm guessing 600lbft of torque there is only so much of it that the transaxle has to deal with before you lose traction anyways.

Also, what is the car used for?

I’m running Pirelli PZero 275/35/18 prob upgrading to 305’* in the rear. With a substantial amount of weight over the rear wheels she hooks up surprisingly well. I also have a wide track koni coilovers system in the rear. It will not be a track car, just a fun street car and head turner at some local car shows. I know nothing is bulletproof but I just want some piece of mind I guess. I detonated 3 4t125’* including an all out race prepped one, and 1 4t60 before I decided to switch to a computer controlled unit. There’* a local guy here with a built SBC .65e combo he has a paddle shift setup and he takes off in second gear. How come nobody is making the GMR parts anymore? It seems like with the amount of interest I’ve seen it would be a lucrative venture? Whoever produced the 1” chain and input shaft could sell those parts for thousands each. I know Milzy motorsports is advertising a new 1” chain gear set for 1999$ but I’ve heard a few guys broke them already.

If your running this in Fiero, I wouldn't worry too much. 4T60'* are hold up pretty good when launching heavy Bonnevilles. A beefed up 4T80-E in a car that weighs half as much as a Bonneville or Caddy should do fairly good. I think your trans is good at this point, but what are you using for half-shafts? Those are your current weak point.

On another note, I had a friend in high school put a 350 in a Fiero. That was badass. I can just imagine what yours is like.

Thanks. I’ve done all I can with the 65 and I have another one from PATC as a spare. As far as half shafts I went with Mark Williams custom axles they’re larger diameter shafts and I believe he used Porsche ends mated to the gm stuff he guaranteed them to 800hp so he seems confident in them. We’ll see, fingers crossed!!