Does anyone have a ball park figure?

Thanks.

 

It's dependent on too many things. Each setup will be different.

For my 408 / GT70 combination it was around 45hp / psi.

 

The answer is 7% increase in HP for each 1 psi.

 

 

Its very dependant on charge air tempeature...

you can say its more closely related to Density.. roughly a doubling of density is a doubling of power output... thats "If" you wanted a ballpark figure...

 

Yes that's a secondary factor, as in: for every 10 * cooler the air = 1% more power.

Watch these videos... Gale Banks and Keith Maney can tell the story better.

http://www.youtube.com/watch?v=Z3iBKwcQ3Yc
http://www.youtube.com/watch?v=poCsdMrm998

 

You guys are only telling half the story there though.

Yes, from physics we can get to 1 psi = 7% increase in hp, but only if the temperature remains constant. What turbo or S/C can do that? None can. So now we have to talk about the intercooler method and efficiency of the intercooler in being used... Right back to "it's different for every setup"

Yes, we can also get to 10 degrees cooler = 1% increase in hp, but only if the pressure remains constant. What intercooler cools the charge without a pressure drop? None Back to talking efficiency of the setup again.

There can be major changes to these two numbers based on how things are setup, the combination, etc. Useful for planning, I agree, but don't fret if your actual power numbers aren't 7%/1% respectively.

Take my numbers above. 45hp was about 9-10% on that combo. I did have the intercooler bringing the charge to ambient +10 degrees under normal conditions, and had a fan on it (but no AC duct). I also over cranked the turbo to account for the boost drop from the intercooler.

 

I always thought of it this way:

Theoretically:

14.7psi of boost = 2x the density of normal intake
Add twice the fuel to compensate for that.

Twice the air + twice the fuel = twice the power.

100% more power / 14.7 = 6.8% increase per psi

So theoretically, at best you're 6-7% increase per psi, but all factors included, its more likely 3-5% with losses

 

It also provides diminishing returns as boost gets higher. Aside from having to keep your IAT's the same, you won't see a linear 6-7% increase in power as boost goes up.

Take for example an engine that makes 400hp N/A. Add 14.7psi of boost and you get a theoretical 100% power increase. So you're now at 800hp, which is believable. If you add another 14.7psi of boost it probably won't net you another 100% power increase, because you'd then be making 1600hp which seems a bit high. I don't think it's an exponential curve necessarily, but it's just not one linear 6.8%/psi slope.

 

Nice I love the theory of atmosphere (14.7 psi) and the explanation of how it works. Always makes me question the guys that claim big power from 5 psi The above mentioned theory is proof that "x" amount of boost will only make "y" amount of power, science is a beautiful thing!

There is also the argument that "x" amount of boost will create "y" amount of heat, but that is a topic for another thread.