I tore mine down to do what it needed anyway- an AFM delete. This requires new lifters and a cam. Of course, you'd wanna replace all the usual wear items while you're in there (oil pump, timing set, gaskets, etc.). I originally planned on an L33 cam which is a stock Gen3 cam that has the same profile as the Gen4 cam but without the AFM lobes. This would've required no tuning, but it would've been just like stock with the stock power output. A buddy offered me a nice cam for cheap, so that changed everything. Since I was getting the heads cleaned up, including a light shave on the surfaces just to clean and true them, I decided to get .020" shaved off to raise the compression a little and the bowls blended to improve the flow a hair. Since new head gaskets are already on the parts list, I spent a "little" extra on some thinner ones to tighten the quench height. The cam I have is shown to yield around 50HP. The raised compression and mild headwork should be good for around 20HP and definitely more torque across the board. These engines are spec'ed to produce 326HP/348TQ on E85, and 11HP/17TQ less on regular unleaded. If possible, I plan to maximize the E85 tune. So, 326+50+20= 396. A tune is a must and I'm sure 5-10HP could be found in that, conservatively. Between the intake and freer-flowing exhaust, I'm expecting about 400HP at the flywheel. I tossed in a mild stall converter to help make it feel and act even stronger.
So, my main point is that 400HP is easily doable. It's especially easier to do when you weasel other parts in while you're "performing maintenance/longevity repairs".
