Re: 2.5 vs 2.8 vs 3.0 FPR - Saab 900 Bulletin Board - Saabnet.com
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Re: 2.5 vs 2.8 vs 3.0 FPR
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Posted by Justin VanAbrahams [Email] (#32) [Profile/Gallery] (more from Justin VanAbrahams) on Fri, 8 Dec 2000 17:50:20 Share Post by Email
In Reply to: 2.5 vs 2.8 vs 3.0 FPR, Frank M, Fri, 8 Dec 2000 17:13:57
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Actually, it makes perfect sense. The non-turbo runs lower-rated injectors at a higher pressure than the turbo. This results in ultimately less fuel flow. The reason for this setup is the FPR maintains a given fuel pressures *above* the existing manifold pressure - assuming you net *maybe* 1 or 2 psi of positive pressure (I doubt the intake manifold on a c900 is that advanced, actually) in the intake manifold on a non-turbo, you'll get somewhere in the area of (manifold pressure+FPR rating) 45-46 psi of fuel pressure at the injector. On a turbocharged car, [positive] manifold pressure will vary between 0psi and 13psi (on a Carlsson, for example). That means the fuel pressure will vary between (manifold pressure+FPR rating) 36psi and 49psi. Were a turbocharged car to run a 3.0bar FPR stock, you'd be running close to 60psi. Saab likely decided that this would be excessive pressure not only for the injectors, but potentially for the fuel rail and fittings as well. I'm not a physics major, but I'd also guess that running high pressure like that might heat the gasoline excessively as well.

Being a computer guy and not a car guy by trade, this is a guess. But it seems reasonable to me based on what I've read...

-Justin

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