Total hp?

for a stock engine,i would go in the 300 hp range.

450 is fine. Once you get past 500 you are on borrowed time. many people do it and it lasts because they don't drive it much, if you put a lot of miles on the car and are often in boost, something will give.

still you dont want to go more than 300 to 350 hp,450 will blow it for sure.

Well... If I am not mistaken... The modular 4.6L v8 came factory with 300 horses from the factory... Mild tunes with a reprogram, cat back, and cold air intake should put you somewhere around 350hp. Now, to your question. Is 450 reasonable... yes.. Shelby, Saleen and Roush were making 500-550hp mustangs with just bolt-ons. Now food for thought... Will the transmission and diff support that much??? NO... Factory driveline was only rated at a max of 350hp... So if you are going to go much higher than a mild tune, make sure you plan to beef up the tranny and diff too..

horsepower doesn't blow engines. compression (pressure) and detonation do.

no really just watch your rpms and dont over rev it set a tach at abot 5200 rpm it shouldnt hurt anything get alow end cam for max power at low rpms id the best for torque beat them out of the hole with nitto drag radials and a 373 gear

Basically the stronger the engine the more power it can handle. A stock engine can only handle so much power, at some point its gonna need to be beefed up to handle more power. The parts that are in your engine now are only so strong, replacing them with stronger parts will allow your engine to work harder and make your more power. The best person to answer this would probably be a dragracer( not a street racer, but a real drag racer). These guys drive their cars to the limit, they've seen engines break and they know where to beef them up to make them stronger.