The old fuel system was a dual intank ractronix kit running stock lines, stock regulator and a hobb switch to engage the 2nd pump at 5psi.

The new fuel system consists of dual walbros runing at the same time into a aeromotive 13101 regulator which is boost referenced 1:1 and set @ 43psi.

Both system are using versafuller with 96lb injectors.

What will i need to change in the tune to compensate for the constant fuel pressure?

Thanks!

 

Nothing. The factory fuel system uses a 1:1 front mounted regulator with return line and maintains a constant 43.5psi across the fuel inectors.

Why did you swap in the exact same system? and why is the 2nd pump running all the time? 95% of the time it'll be unnecissary and just wear out faster, be noiser, and put more heat in the fuel tank. Also it's not a good idea to massivley oversize the pump because at idle and cruise all that flow might overwhelm the regulator and return line. Progressively adding flow as it's required is the way to go.

 

Assuming his return fuel line is big enough he shouldn't have to worry about the pumps overwhelming that regulator.

 

A stock regulator changes the pressure with vacume doesn't it?I know fuel pressure with a stock regulator doest go above 43.5 until u go WOT so the WOT part of the tune shouldn't change but what about part throttle and idle? i just been out of the lt1 world for too long
I also should have added that the stock lines were replaced as well with -8an feed/ -6an eturn.
here is the pic of the current system

 

Both regulators operate the same way.

1. Vacuum decreases fuel pressure
2. Boost increases fuel pressure

For instance when my car (stock regulator) was pulling 16" vacuum at idle it was at 37psi

When it was pushing 10 pounds of boost it was running at 53psi

I agree that your tune will require very little change as long as the fuel pressure is kept at the stock psi.

If at some later time you decide to increase the fuel pressure you will have to completely retune the car. It will affect almost all fuel tables as well as starting.

 

Crap for some reason I didnt think the vacume played any part on the new regulator. Thought it was only sensitive to boost. Feel pretty silly now lol

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The regulator simply maintains 43.5psi across the fuel injectors (from the fuel pressure to the manifold pressure). If you have 10psi of boost in the manifold you need 10 more psi of fuel to maintain 43.5.

Same goes with vacuum. 1"hg of vac = 2psi. So if you have 10"vac in the manifold you only need 38.5psi of fuel pressure. Since this Delta pressure is always constant the PCM just needs a pressure constant and it always know how much fuel is entering the motor.

 

Why do you say this? You're just changing a constant, if it's compensated elsewhere in the 'equation' then it doesnt matter; the PCM still know how much fuel is being delivered.

The formula is sqrt of (new pressure/old pressure) x old flow rate = new injector constant flow rate

for example if you change your fuel system from 43.5psi to 58 psi, you'll enter an injector constant of 110.75 #/hr instead of 96.

 

So here is the question then: if fuel pressure is set above the stock 37-38psi will run rich even with a retue???

The reason I ask is I put in a Lonnie's double pumper and have, with a stock FP regulator, my fuel pressure at idle with vacuum tube is at 44psi like the OP. It was 38psi before and ran like a champ.
I have tuned it 6 ways to Sunday and it is great everywhere except at idle and light, light cruise. It fouls plugs within minutes with an AFR in the high 11s.

If the OP has an adjustable regulator the key might be to lower to the factory 37-38 psi.

 

The stock delta fuel pressure is 43.5psi (3bar), not 37-38psi. The PCMs fueling calculations are based on this assumption, so if the pressure across the injectors is set above 43.5psi, it will want to run rich, but the fuel trims will correct for this (as much as they can), after their corrections are maxed out it will run rich.

You can however set your fuel pressure at anything you want if the injector constant in the tuning is rescaled appropriately using the formula in my last post.

 

Two pumps should only cause a problem if you're running them both at the same time at idle (ie. the FPR can't bleed enough fuel back to the tank fast enough to control the pressure). If you're seeing 44 psi with the vacuum line attached then you're probably running around 50 psi with no vacuum. You may try increasing your injector constant by ~15% to compensate if you can't get the fuel pressure corrected.

 

That is exactly what is going on. It is 44psi w/ vacuum line and 50psi without.

I thought is was a leaky injector/s and was going to check that when the snow melts but now you have me thinking the install was done wrong and both pumps are on all the time.
Thanks

 

Marcin, you're back in the game? Thought you parted out your old car dude? Well glad to see ya back? You still blown or did you go turbo this time? Sorry for the hijack but I concur what others have said. LOL

 

Typo.

It's the other way around. approx. 2"Hg = 1psi.

That way, 29.93 "Hg (1 atmosphere) = 14.7 psi = 101.4 kPa

 

You would adjust the constant by 7.2%.

(50 / 43.5) = 1.15

(1.15)^0.5 = 1.072

Flow varies with the square root of the pressure ratio.