Fuel press? and boost

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Jul 17, 2003 | 10:02 AM

Cool28

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From: Barto PA

Fuel press? and boost

Ok I been having a problem here of late. Been talkng to a guy that I heard knows his stuff and is built a engine for a friend of mine. I have hp flatlining at 5300rpm and flat till 6300rpms. I thought it was Valvesprings or heads and hes say its not heads and he really doubts valvesprings. He was saying it could be my Fuel pressure. He said once you get into a dif atmophere that you need Fuel press to atomize the fuel better. He thinks I need to up my fuel press. Its at 60psi and I dont have the boost ref on. I was wondering does that sound like a good reason. It doesnt take much for me to try it.

Jul 19, 2003 | 06:07 PM

2001CamaroGuy

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Re: Fuel press? and boost

When you pressurize the intake, you actually make the injectors flow less...

For every 1 psi of boost you add, you need to add 1 psi of fuel pressure to keep the flow rate (of the injectors) from dropping (ex: 9psi boost = 69psi of fuel pressure)...

The exact opposite happens when you pull vacuum. The pressure in the intake drops and this makes the injector flow rate increase. Since the LS1s don't have a manifold referenced fuel pressure regulator, the IFR (injector flow rate) table in the computer is adjusted (set leaner) to reduce fuel flow as vacuum increases.

Jul 25, 2003 | 06:39 AM

AG Formula

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From: Norfolk VA

Re: Fuel press? and boost

Sounds more like the valve springs are weak. But you did not give enough info on your setup to really give you a good answer.

How much boost?
What size injector?
How are you tuning it?
What is the A/F doing when it goes flat?
Have you upgraded the fuel system at all?

AFPR is one way to control fuel on a FI car, but larger injectors with enough pressure can also work.

Jul 25, 2003 | 02:32 PM

Cool28

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From: Barto PA

Re: Fuel press? and boost

i have 7.5psi, #42 injectors, mti tuning, the a/f just gets richer alittle till i let off. I have a intank walbro 340 and a inline 255 pump.

Jul 25, 2003 | 08:40 PM

AG Formula

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From: Norfolk VA

Re: Fuel press? and boost

Sounds like my fuel setup, rich is safe. You are using a WB O2 to measure the A/F. The stock O2 is crap except at 14.7 A/F. And down at 11.X where you want to be they are way off.

It sounds like they turned off COT. Do you know if they did?

Jul 25, 2003 | 09:01 PM

Cool28

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From: Barto PA

Re: Fuel press? and boost

nope dont know if they turned that off or not. I 12.5 where it peaked and down to 12.1 when I let off. this was with a wideband. I just wish I had the power to 6200 lol. I would be flying

Jul 26, 2003 | 12:09 AM

MIGHTYMOUSE

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From: Virginia

Re: Fuel press? and boost

if your tune is right on your a/f target, then its right, reguardless of fuel pressure.. as long as you are somewhere between 40 and 80 that is.. (which you are)
maybe you have an exhaust restriction?