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WERK I WERK I is offline
Forced Induction Junkie
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Join Date: Jan 2003
Location: Wisconsin
Posts: 3,291
The formulas for calculating the flow injector requirements have been based on a generality, specifically BSFC. The .65 BSFC used in the forced induction example would be a worst case example. Turbocharged engines generally fall in the range of .55-.65 and supercharged engines fall in the range of .50-.60 for their BSFC's. Without the engine on a dyno, that number can't be more accurate. I'm afraid the 10% figure you suggest in increasing the fuel flow is a tad off. Increasing horsepower from 180-200 (depending which engine) to 300 is a 50% jump in power, just how are you going to generate that much of a jump with a meager 10% increase in fuel? Also, don't forget superchargers and turbochargers are make power it takes power.

Without an engine dyno, this is all conjecture at this point. It can provide the BSFC for that engine being tested and modified. I would rather side on the margin of safety in using an induction system that was designed for forced induction than one that was not. We haven't even gotten into the weaknesses of the 911 SC CIS, such as the air box, warmup regulator and injector lines. None of which were ever designed for positive atmospheric pressures and fuel pressures that high. Does the owner have a "blow-off valve" in the air box? You know that has to go. 230PSI on those plastic injector lines? Good luck with that.
How does the fuel distributor behave with pressures that high? I don't want to hear, "it should be fine". There's nothing worse than seeing an engine running, suddenly being doused with fuel and catching fire.

Don't be afraid of the is your friend, some say it is god.
You have to use it to get in the ballpark in building an engine meeting your target goal. If all you use is conjecture, it will wind up being very costly in time and money and customers. Turbo maps, injector flow rates/characteristic, fuel pump curves are put there for a reason. Use the math. It is your friend.
'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 01-24-2010, 06:09 AM
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