There are 2 aftercooler designs actually, without including water injection. LHT Performance in FL, and KLR in Tennessee.

LHTs looks extremely promising.

Either way, it still most likely isnt going to happen. It would take more displacement, a ton of boost, some sort of cooling, completely built motor from valve cover to oil pan...and it still most likely wont come close. A 400whp SC'd 4cyl would be INCREDIBLE. Hell, a 300whp no-nitrous SCd car would be a friggin blast.

Im telling you man, if you want 400whp, go turbo.