No experience with their diesel motors, but I have seen quite a few gaser's. All LS stuff (LS1, LS2, L76, LS3 and L99) and there is no-way in hell I would ever put one in something I own or recommend one to anyone I didn't absolutely hate.
Seen or heard first hand everything from crappy machining to mismatched parts (wrong heads, intake manifolds etc...).
The last LS2 I saw was installed by a dealer (06 GTO) because the warranty wouldn't spring for anything else. Car was a complete dog compared to before the repair and after being repeatedly turned away and told nothing was wrong we threw her on a buddies dyno and she put down 260 when a bone stock LS2 in a M6 GTO should make roughly 340 to the tire (I recently sold a stock bottom end LS2 06 GTO that made 483 rwhp on motor). No-one wanted to help this guy out, even after tear-down and showing the motor was built with the wrong heads and cam.
Poor guy ended up out of pocket for heads, cam, valvetrain and labor to get his car back to performing like a stock 400hp/400tq car should. Everyone's answer was that it was a working, running motor and didn't matter whether it was put together spec'd like a factory LS2 or not. They sold a LS2 and it had a LS2 block so the performance of the motor was inconsequential.
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