LT1 fuel pressure

[Everett Vassar]

What is optimum fuel pressure for LT1 ? I haven't learned how to lengthen or shorten injector duty cycle with the laptop yet, but I guess I can make some rich/lean adjustments with fuel pressure?

[Ed Wright]

From the factory: 45 to 47 psi, with the vacuum hose off the regulator, & at WOT.

[Dan Fahey]

Originally Posted by Ed Wright

From the factory: 45 to 47 psi, with the vacuum hose off the regulator, & at WOT.

Mine is 38 to 43psi with vacuum hose!
Using LS1 Injectors.

D

[Ed Wright]

Originally Posted by Dan Fahey

Mine is 38 to 43psi with vacuum hose!
Using LS1 Injectors.

D

Dan, I know you are a mechanic, so I'm going to explain it.
Should be no manifold vacuum @ WOT, therefore, WOT with the vacuum hose connected is the same as testing in the shop with the vacuum hose removed from the regulator. I have had many LT1s through my shop, and don't remember seeing one with only 43 psi. Maybe your gauge, or you have a Walbro pump?

And Pure Stock rules allow different injectors?

My LT1 car has 60 psi.

[Dan Fahey]

Originally Posted by Ed Wright

Dan, I know you are a mechanic, so I'm going to explain it.
Should be no manifold vacuum @ WOT, therefore, WOT with the vacuum hose connected is the same as testing in the shop with the vacuum hose removed from the regulator. I have had many LT1s through my shop, and don't remember seeing one with only 43 psi. Maybe your gauge, or you have a Walbro pump?

And Pure Stock rules allow different injectors?

My LT1 car has 60 psi.

I had LT1 Injectors and replaced them with 24lb LS1’s.
IHRA tech went over the car several times and passed inspection.
They are a direct replacement using same Stock Fuel Pressure.
Using a Bryan Herter high test tune and seems to work fine.
Though could use a good Dynoing with current PS cam.

Still using ODB1 and TunerCat to make little changes.
Using high pressure Walbro Fuel Pump and adjustable Fuel Pressure Regulator.
Set the pressure range from 38/43 psi which is the Stock setting.



Dan

[Rich Biebel]

I ran my LT-1 stocker with 50lbs of fuel pressure and at that time ran 24lb Accel injectors. It went 10.50's in real good air at 125 in the then separate A/FIA class.....Car was about 200 lbs over the weight minimum for the class....


After selling the car I was given the opportunity to drive it again for 2 weekends. It still was run with around 50lbs of fuel pressure and had bigger injectors. It was a little heavier than when I ran it and ran 10.50's in real good air.....running B/SA.....It had a better engine and much better fuel map tune up. The car ran some 10.20's at Atco before the HP was hit a while later.

[Ed Wright]

Dan, your factory injectors were 24lbs. '97 &'98 LS1 injectors are rated at 28 lbs. '99 & later are 26lbs. Stock LT1 cars are all too rich @ WOT from the factory. More injector won't gain you a thing. If not tuned for them, they will slow you down, unless there were issues with your factory injectors.

The LS1 uses 58 to 60 psi, which of course makes them flow more in use.
Not likely the IHRA Tech guys would think about checking the numbers on your injectors, nor have the numbers on file, or may not even care.

There is no power there, running LS1 injectors at the fuel pressure you are using.

If the IHRA rule book does not state that you can use different injectors in Pure Stock, even if the tech guys don't notice, and you are using them, you are simply illegal. Sneaking something past Tech simply does not make it legal. If the tech guys knew enough about it, and cared, the LS1 injectors do look different. I would know if I saw it. No power there, just illegal.

[Ed Wright]

Rich, higher fuel pressure atomizes fuel better. Better odds of every cylinder firing every time. In the real world they seldom do. My GM Calibration Engineer friend was telling me the power & emissions improvements they saw when developing the LS1 engines when going from the ~ 36/46 psi fuel pressure used with the LT1, to the ~60 psi for the LS1.
I had to go to 42 lb injectors for my LT1 Super Stock engine, to get the injector duty cycles comfortable @ 45 psi. I started thinking about that. I went to 36 lb FAST injectors @ 60 psi. They tested the same there as the 42s @ 45 psi. On my old Dynojet chassis dyno, A-B-A testing, dialed the air/fuel ratio to the same 12.8-1 it likes on C11, picked up 9 hp at the tires. Obviously some misfires going on we could not here. My GM guy predicted "8 or 10", saying "They all miss some, all the time. Has to be bad to hear it."
I thought the gains had to be a fluke when I changed them. Changed them back (as in A-B-A testing) and it dropped back off. Changed injectors, tune & fuel pressure again, picked it right back up. Had to call him to thank him. LOL

[ss3011]

The formula for determining a different injector flow rate by changing the fuel pressure is :

(Square root (New Pressure/Old Pressure)) x Old Flow Rate = New Flow Rate


So if you go by Dans' combo where he stuck in LS1 injectors (24lbs@58psi) and he lowered the pressure to 43psi . The rating would now be (21lbs@43psi) . Basically a wash compared to a stock LT1 injector which is (22@43psi) .

Its important to know what pressure is used when comparing injectors

[Ed Wright]

The LT1 & LS1 injector flow rate data is certainly different that I was given. Guess maybe all GM engineers don't all have the same data. Do agree that Dan made a useless change to his now illegal car. LOL