LS4 Swap - Struggling to decide on transaxle

Hey folks-

I'm working my way through the frame off restoration of 3154 which will include an LS4 swap and I'm almost at the point to decide on my transaxle. My UN1 is in good shape, it was shifting fine when I removed it from the car. To my knowledge, it has 37K miles on it and I changed the gear oil on it when I got the car. I've done a ton of research and know about a few failures, but if I'm going to stay stock on the LS4 (except for fixing that crappy parts about that engine), do I really need to go Porsche transaxle? The cost increase is considerable so it will delay getting my car on the road which is already delayed by a house move, etc. Curious to get some thoughts here. Apologies also but I didn't see a swap forum so mods please redirect me if required.

Thanks!
Jake

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Originally Posted by mowpow

Hey folks-

I'm working my way through the frame off restoration of 3154 which will include an LS4 swap and I'm almost at the point to decide on my transaxle. My UN1 is in good shape, it was shifting fine when I removed it from the car. To my knowledge, it has 37K miles on it and I changed the gear oil on it when I got the car. I've done a ton of research and know about a few failures, but if I'm going to stay stock on the LS4 (except for fixing that crappy parts about that engine), do I really need to go Porsche transaxle? The cost increase is considerable so it will delay getting my car on the road which is already delayed by a house move, etc. Curious to get some thoughts here. Apologies also but I didn't see a swap forum so mods please redirect me if required.

Thanks!
Jake

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You may want to give Josh Shattenkirk at DMCMW a call. He's also on the board here, but not sure if he checks it regularly.

He's done quite a few LS swaps now with both the standard UN1 and Porsche transaxles, so he may be able to advise which would be appropriate in your case. If I had to guess I'd say for a stock LS4 you would be fine with the UN1, but if you start talking mods to add more power then you are probably going to want to upgrade the trans.

If the LS is stock and you don?t drive like a teenager, you will probably be fine. Talking to Josh is probably good advice.

Delorean Midwest has a nice video of them reviewing an LS4 with a UN1 transmission. https://youtu.be/-Szy89fo5EQ?si=j4iSBKXWK-WPlexw

At 3:20 they talk about the stock UN1 having an upgraded spline coupler and handling 300HP.