I'd think 450 RWHP is pushing it for the W58..
I have read about guys pushing 400+ for awhile with it, but it ends sooner or later. I would agree with Matt when he said about 375WHP is the reliable limit.
Here is a usual comment on the supra/lexus forums regarding the W58.
Quote:
and from experience, the w58 blew its guts out for me at 380whp.
and before that no joke i screwed 2 or 3 clutches up before the trans gave out. honestly dont beat on it, dont dyno it hard or your asking for it.
and im not kidding. i went with a v160 because i was sooooo freaking tired off all the problems, plus, i was about to make more power.
Now.. I have no personal experience with the W58 myself. I thought about switching to one for awhile in the lexus but my slightly built auto trans couldn't even handle shifting at WOT. So I decided to stay away.