how much power can the low pressure piston pump handle. i would really like to stay with a mechanical pump for reliability reasons. im shooting for 350-400 hp. any advise would be greatly appriciated

 

It'll support the 350-400hp you're after. It's good for at least 15psi at idle. Some have even seen them run at 17-18psi once a pressure gauge is hooked up. I haven't heard of anyone drawing it down to 0psi. That's easily accomplished with the stock diaphragm lift pump which is only good for about 3-5psi at idle. You can clearly see a difference between the two pumps. Not to mention, the diaphragm can tear in the stock pump or any stock replacement. No diaphragms to worry about in the piston lift pump.