Max is depending on your current compression and fuel type. You will get a variety of answers. What is your goal? Additional 300HP? 500HP? 1000HP? Then it gets into fuel delivery, timing, plugs, piston design and so on. N2O can be fun and addictive - but can be costly depending on the set up.

I now prefer to run boost as a power adder. Power is always there when needed, no bottles to fill and change, no fuel changes, less changing of plugs, no bottle blanket/heater, and etc. etc. etc.

 

Depends on the current compression ratio and ring type....but the crank and rods should be good for 400-500 HP without a problem.

Also depends on the block ...2 or 4 bolt main??, 2 bolt I wouldn't go over 325 HP or so. Same with Plasma Moly rings, use Hellfire rings or similar if you want to shoot over 325-350 HP regularly.

How much are you wanting to shoot??

Fuel type/octane will be important also, what are you going to be using??

Completely stock cast crank, cast piston 2-bolt 454 with a cam change will handle 200HP with no problem, your current 150 hp on the forged crank and H-beams with forged pistons isn't even felt by the parts.