spitfun

Does anybody know if there is a formula or chart to find the approximate HP gain per lb. of supercharged boost in a LS 5.7L engine? I know it will be a rough estimate,I would be fine with even a rough percentage gain per lb. of boost if there is such a thing. Thanks Rich

skyavonee

A&A advertises a ~175rwhp increase with their C5 kit, which I think is at ~7psi. So, figure about 25rwhp/psi for a centrifugal supercharger. That number will be lower for a twin screw or roots blower. And no matter the design, there will be diminishing returns as you increase boost, due to heat issues (unless you add methanol injection).

These are rough numbers and general rules of thumb.

FASTFATBOY

A general rule is 10hp per 1 psi of boost.

skyavonee

^ That's closer to what a 2.0L Miata gains... it seems way too low for a 5.7L LS engine. Do you think it takes 10psi to add 100hp to the C5?

As another data point, Magnuson advertises ~120rwhp with 6psi on their C5 "hybrid-roots" supercharger, which comes to 20rwhp/psi.

FASTFATBOY

"General rule"

bjankuski

(Boost in psi + 14.7)/14.7 × base engine hp

spitfun

The car makes 703 RWHP which equals about 800HP at the crank (approximately). From what I've been reading I think the boost is closer to 18-20 HP per lb.,if not my LS1 would be making about 650HP at the crank normally aspirated-that seems high,what do you guys think? Rich

Quickshift_C5

Agreed. 10hp per lb is not even remotely close. General rule for a miata maybe.

skyavonee

I'm actually a little confused now. You already know how much power the car makes, so then are you trying to figure out how much boost it's running? If so, just find someone local who uses the Torque Pro Android app (or other OBD-II reader app), and you can view boost in real time as you drive. Although, with a centri making that much power, you might need a long, straight stretch of road in order to reach peak boost. Also, this assumes you have a MAP sensor that can read positive pressure, which maybe isn't the case for you?

Otherwise, if you know both the power and boost, you can calculate your own rule of thumb.

spitfun

Thanks for all the help guys... Rich

bjankuski

800/((14.7 + Boost psi)/14.7) = base engine HP

Take base engine HP / .85 to account for supercharger loss that gives you real engine HP non boosted.

800 - Non boosted HP = differential

Differential/Boost PSI = HP per lb of boost.