Yet another fuel pressure related thread.

I installed the Vortech FMU over the weekend and tested it by creating boost with a Mityvac (yes, you can use it to blow as well as suck). At 2 psi of boost, my fuel pressure gauge registered 50 psi, and at 6.5 psi of boost, I got 95 psi FP. Now (95-50)/(6.5-2) = 45/4.5 = 10. So apparently Vortech sent me a 10:1 disk when I ordered an 8:1. Or possibly, there is enough error in my gauges to show a false 10:1 reading.

Is it possible that the high pressure Walbro pump I installed affects the delivery rate of the FMU?

 

IF you have an autometer gauge, it's practical that's where the error lies.

 

so Mityvac blows and sucks eh?...

 

Yep, that's what I said. A-hyuck.

 

Stephen,

If you want to be sure, I'd call Vortech and ask them
what size diaphram you need in the FMU to get 8:1.

There are no part numbers on the diaphram so the only
way to tell is to measure the diameter of the diaphram.

When I called Vortech they were pretty helpful
and disassembling the FMU to get to the disc/diaphram
is pretty easy.

-Victor

(PS I did this before but regretfully forgot the right
diameter)

 

I pulled the diaphragm out and measured it. It is the 8:1. I calibrated the pressure gauge I was using to measure the boost pressure and found it was registering 6.5 when the pressure was actually 8 psi. So taking that into account I get a pressure rate of around 8.5:1, which is more reasonable.