Boost Required for "X" Horsepower Calculator

Horsepower is related to airflow and airflow is limited by the pumping capacity of a given engine displacement . Given a certain engine displacement and certain other factors you can calculate how much boost will be required to achieve a stated level of horsepower. Then it's off to the compressor maps to check airflow v. pressure ratio.

In choosing a particular turbo you need to know how many Pounds Per Minute or CFM the turbo compressor map indicates for a particular pressure ratio (boost pressure). You cannot make more horsepower that your turbocharger can supply...For instance if your turbo peaks at 360 horsepower (about 44 pounds per minute) it simply is not going to make any more horsepower no matter what the calculator says.

Above is Mike Geokan's Bonneville Bullet, back from Bonneville...washing off all the salt. If you are just credit-carding your way to glory you can skip this calculator. If you're a builder, fabricator, or a "designer", whatever that means, then sit down and do the math. If you don't do the math you will always pick the wrong turbo for your engine. We can't tell you how many people have called us up telling us they would be happy with 8 pounds of boost without knowing if the turbo they were planning on would have enough airflow at 8 psi to even meet stock hp levels.

Go figure. We do.



Boost and Airflow Calculator

Peak Horsepower Desired horsepower
Air Fuel Ratio :1 Typically 12:1. Enter numbers i.e. 12, 12.5, 11.5 etc. Do not enter the colon (:)
B.S.F.C.

Brake Specific Fuel Consumption

BSFC can be from .5 to .65. Typically .55
Charge Temperature (Post intercooler)

Deg F Typically intercoolers are used to drop compressed air discharge temperartures. A typical entry is 130. To run calculations on this use our Intercooler Calculator.
Volumetric Efficiency Volumetric efficiency can be above or below 1.0 A typical entry might be .95
Peak RPM Enter peak RPM
Displacement in Cubic Inches Engine displacement in cubic inches

PSI Boost Required
Pounds Air/ Minute for Desired Hp CFM for Desired Hp
 

Jeff Hartman's Turbo Book

For a comprehensive look at turbocharging we recommend Jeff Hartman's book. It has extensive formulas and plenty of up to date pictures to guide your project on its way. It covers every aspect of turbocharging. Probably a good idea to read up on things before you start cutting, welding, and spending money.

It features Mike Geokan's Bonneville Harley engine on the cover when the Bonneville Bullett's turbo system was being designed.