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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Originally Posted by WERK-I View Post
Maybe you could find a used 930 (3.0-3.3) CIS? I've seen them on e Bay and on the Pelican Parts forum, maybe even a Mercedes or Volvo system may cut it. Search for one matching your HP requirements, not your engine displacement.

Your current system simply is not going to cut it without extensive modifications.

Let's say you have a 200HP 3.0liter 911SC
Injector Flow Rate (cc/min) = Engine HP x BSFC x 10.5/Number of Injectors x Injector duty cycle

Injector Flow Rate (cc/min) = 200BHP x .45 x 10.5 / 6 x 1.0
Injector Flow Rate (cc/min) = 157.5 cc/min = 157.5ml/min

Look at the numbers for a Supercharged 300HP 3.0 liter engine. Keep in mind your BSFC will go up due to it being a supercharged engine.

Injector Flow Rate (cc/min) = 300BHP x .65 x 10.5 / 6 x 1.0
Injector Flow Rate (cc/min) = 341.25 cc/min = 341.25 ml/min

I might be able to start to understand the above as math is not my strong suit.

The BSFC has to do with the design and efficency of the motor and we have to adjust it for a forced induction motor. A low pressure motor probably uses about 10% more fuel than a N/A motor. Thus, a jump from .45 to .65 seems a lot more than I would guess and suggests such a motor needs 50% more fuel per every HP made.

Again, I am not a math wiz and I could be off on this.

So if a NA 200hp motor 'might' need 157cc/min (depending on how efficiently is operates or its BSFC),

a NA 300hp motor might then need 'about' 225cc /min if it operates at the same BSFC.

If a low pressure supper charged motor needs 10% more fuel than the N/A motor it seems it might need about 250cc/min.

Again, it depends on how much fuel the motor needs per HP and that varies.

How one get's there is the question. Changing an SC to Turbo specs it probably not going to be that simple and may be more than is needed as a 930 can supply enough fuel for about 400hp.

AFRs are a function of the injectors, system pressure, control pressure, spring tension around the internal orifices & there height, and the profile/programing of the metering cone and assembly. An SC metering plate is probably going to advance at a different rate on an SC than a turbo even with the same WUR specs.

It is going to probably be a trial and error exercise unless a used 930 intake system is purchased and it to will still need tweeking.


PS: Injecting fuel into a supper charged motor running about 70psi in to an pressurized manifold running at about 7 lbs boost will require a higher fuel delivery rating of about another 10% I suspect. Thus, the est of 225 goes to about 250cc/min.

This could be off if the est of BFSC is off.

Again, I could be off on some of this stuff.

Last edited by 911st; 01-23-2010 at 10:33 PM..
Old 01-23-2010, 09:47 PM
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