Flightplan

Assume I have a Mercury 400 R And I have a true 400hp

My 400R runs 32 pounds of boost (yes,thats the rumor).

What is my naturally Aspirated power, NO BOOST?

Please show me the math.

I know someone here knows the formula.

tzrider

I'm going to make an assumption that the 32psi rumor refers to absolute pressure, 14.5 atmospheric plus 17-18 psi boost pressure. As a rule of thumb ( and its kinda broad) you can use 10bhp per 1 psi boost pressure. Without the forced induction it equates to roughly 230HP

tomcat

I've never tried to put rumors into formulas but I'll assume that it really is 32 psi boost.

Start with a perfectly good 200 HP NA engine. Now reduce it's compression ratio. Next, add the intake plumbing you need to supercharge it (and exhaust plumbing if its turbocharged) thereby reducing volumetric efficiency. You just reduced the engine's power to say 160 HP (no boost yet). To bring that up to 400 HP you need a density ratio of 2.5. Divide that number by 0.8 because you would be lucky to have an intercooler that was 80% effective. That gives you a pressure ratio of just over 3:1, which is about 30 psi of boost.

Just an example, you need real data...

hogie roll

I highly doubt it's that high. Since we experience 14.7psi at normal atmospheric conditions, if you add that much boost pressure you will add 100% more power than naturally aspirated. So 14.7psi equals 2x power, 29.4psi equals 3x.

If a 400hp engine with 32psi boost were NA it would make 400*14.7/(32+14.7), or 126hp.

It's much more likely that it's 32 psi absolute, which is only 17.3psi beyond normal atmospheric pressure. If that's the case then the engine makes 184hp NA.