This is a bit of a long post but hopefully it will help some guys that are having trouble running larger injectors (mostly 39 lb injectors) with a SFMU only.

I finally have the car back up and running. It was down for a blown Cometic Head Gasket which was causing low compression. Cylinder #4 had only 120 psi of compression due to the bad gasket.

My car has a VT Engine 8.8 to 1 rebuilt engine in it so compression numbers should be around 190 psi. Yesterday, I started the car, let it warm up, and then redid a compression test on it. Cylinder #4 as well as all other cylinders are back to 190 psi.

During my initial test drive it felt as though the car was lacking some power under normal acceleration (no boost). I also noticed that my gauge was going pretty lean when I initially hit the gas and then it would come back rich. My Vortech SFMU contained the 2.72 disk and ring combo. This provided decent fuel readings under boost but the car didn't feel smooth.

I decided I did not like the way the car felt and swapped out the 2.72 disk and ringn for the 3.62 disk. I also installed the optional bleed and check valve. I set the idle pressure according to my pocketlogger STFT and LTFT so that the readings are -1/+1 on the STFT and -13 on the LTFT. I also knew that the current disk would provide to much fuel under boost and opened the bleed valve two turns.

I am very happy with this fuel setup and the car is really responsive. I was equally impressed with the readings off the o2 sensor as it is constanlty .96 to .98. Take a look at the data logs below.


Summary of Fuel Setup:
39 lb Injectors
3.62 Disk
Bleed/Check Valve installed - Two Turns Open

First Run:



Second Run (Notice fuel picks up right where boost begins on a 16g - Approximately 2800 rpm):




--Kurt