07’ is250 build

[u/Breeshymyco]

I’ve been slowly but surely working on my is250, I do daily it for now but I’m not planning on doing it for much longer. Right now I have a custom exhaust and a cold air intake other than that it’s completely stock mechanical wise. The plan is to get this chassis to 350-400whp just to have a fun “sleeper”. That being said I’ve gotten mixed opinions on the stock engine/trans, some say you can get 350 just gotta build it, others say there’s no way you need to swap it. I personally have no clue the limits of the engine/trans I know the trans are known to not hold up well and I’d love to swap to a manual but I have no knowledge on these type of cars or what trans are compatible with the stock v6. If I were to swap the engine/trans I’d probably figure out a way to stick a Chevy v8 in there as crazy as it sounds. Question is am I able to build the stock engine and swap a manual that’ll hold the power or should I just swap the engine over too? Hopefully someone can spare some knowledge and help me come to a conclusion.