With proper parts selection, I see no reason why a 318 couldn't reach 1 HP per square inch.
The secret is in the heads and the cam!
The lift of a stock 318 cam is .373. Yeah. The valve springs could almost be compressed by an 87 year old dude with arthritis.
The 318/5.2 Magnum was rated at 230 HP, a number that could easily be boosted with better heads and intake, headers and a decent cam.
