A question on fuel (JRSC)

[Sonnyballs]

Hi Guys,

Sorry if this has been hashed over before, but after researching this place, Club Si, and Endyne's boards, I've obtained tons of useful information. Now, I just need to sort it all out.

Car: 2000 Civic Si
Current mods: Integra Type R head (stock Si cams)...long story, Skunk2 cam gears, NOS fpr (set at stock setting).
Plans: JRSC 6psi kit, Exedy Clutch, J&S Ultra Safeguard, gauges, possibly a header, etc. I do not plan on boosting more than 6psi though.

Questions:
1) From what I've read, the stock flow rate of the Si's injectors is 240cc, right?

2) It appears that most people are setting their fuel pressure at about 50-55psi at idle using the JR FMU. The JR's FMU has a fixed 5:1 rise rate. This means that for every psi of boost, it adds 5psi of fuel pressure.

3) If that's the case, at 6psi of boost with 52psi at idle, there would be 82psi of fuel and at 7psi, there would be 87psi in the system? Damn...isn't that a bit much for the stock system?

4) If I were to get 270cc or 310cc injectors, I could drop the idle fuel pressure by about 12% (270cc) or 29% (310cc), right? The amount of fuel sprayed is a function of the flow rate of the injector, the amount of time it is open (fixed by ECU), and the pressure behind it.

I think I saw Larry at Endyne say that he recommended 310's on a 6psi kit.

Thanks in advance for any feedback.

Sonny

[Marc]

You are correct. The pressures are quite high with most rising rate setups. You can use larger injectors to bring down the pressure but it's recommended to have some form of fuel management to control the pulse width at different rpms.

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Marc
1997 Civic EX
The supercharger is gone. Get ready for the turbo.
Want to know why I got rid of the JRSC? http://crx.honda-perf.org/horror/jrsc.html

[Holden]

First off, you don't need a J&S at all at 6psi boost. Even the J&S fans would probably agree with that.

Second, rising rate FPR's (JR's, Cartech, all of them) go by manifold pressure, not boost. Manifold pressure is almost always higher than boost. My 6psi GSR hits 8psi in the manifold, sometimes going to 9psi in cold weather.

So.... a 55psi idle, 62psi @ 0" vacuum setup (don't forget the FP starts rising BEFORE 0" vacuum) with a 5:1 rise rate will more likely raise FP up to 62 + (5 * 8) = 102psi.

Smaller exhausts/stock cats could go higher. Big exhaust/straight pipes could make it go lower. Both by raising or lowering the manifold pressure due to different back pressures.

Yes that's a high pressure, but lots of people are doing this. With a good fuel pump, you likely won't have problems. If you get a more adjustable FPR, you can lower the high end FP down into the 90's on stock injectors.

I would worry about being too rich with larger injectors on a 6psi setup. You may need to bypass the OE FPR to lower FP enough or possible might need a fuel controller like a VAFC.

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Greg Holden
96 GSR, JSRC @6psi, AEM CAI/RSR 4-2-1/Greddy PE, Cartech 20005/Walbro GSS-342/TPS Mod, JR BTC, KYB AGX/H&R OE Sport/ST 19mm Rear Swaybar
Best 1/4 ==> 13.937 @ 101.41mph
My JRSC Install Site