Hey guys back again. I have the L67 engine with 100k miles and fixing to buy a 4t65E fully rebuilt to go with it. I'm swapping my 3.4 out of my 03 LS with the L67. My long turn power goals are 300 HP at the crank. Is there anything I am missing or need to take into account? Will the non HD version hold 300 crank HP?

 

The only difference in the transmissions is the diff. The non HD have been pushed just as far as stock HD units and the failure always seems to occur elsewhere with big power (unless you do 1 wheel burnouts).

In terms of holding 300 crank, it'll hold, but not forever. Just look at the 5.3L cars with the slightly modified 4t65 at 300. They live decently, but most die pretty quick. I'd definitely start saving for a moderate performance build on the trans for peace of mind and long term durability.


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Would it be a good idea to take the trans I bought (it's fully rebuilt) and replace a few parts with performance ones? Also I heard I need the passenger side Axel as well

 

You should only need a passenger axle if you get a HD trans (or do an HD upgrade to a non HD trans).

That's a hard spot with that trans you got. There are certainly some performance parts you could put in to help it survive longer with 300 hp, but they're going to require tearing the trans down again to do them. Probably more cost than its worth at this point as you'll nearly pay rebuild cost again unless you can do the labor yourself.

As long as you're confident that the rebuild was done properly, I'd probably just drop it in and run it and see how long it lasts. Once it starts acting up (if you even still have the car at that point), then you could rebuild with higher performance stuff. I'd just make sure to pull it when you start noticing issues and don't wait until something grenades itself and takes out half the hard parts with it.