Originally Posted by Jordo!

That dyno claims a baseline of 338 ps and winds up at 408 ps... a gain of about 21%.

Most stock Z's dyno around 275-285 on a dynojet... a gain of 21% on that would put it in the 332-342 range. High, but a few have hit that with full bolt ons, tune, generous correction etc.

So... the reported values are considerably inflated (relative to dynojet numbers) and the proportionate gain, while on the high side, is not unheard of.