I have a fuel pressure gauge hooked up right now so I can see what it's doing while I'm driving. It's usually about 4-5 ish while driving around. During hard acceleration it drops at least 1 psi or more.
4-6 psi is the preferred fuel pressure range for a Q-jet. If the pressure drops below 4 psi at WOT, you need more fuel delivery. Bigger pump and/or lines, or a pusher pump at the rear in conjunction with the stock Stage1 pump
I just tried a different gauge with a lower range for carbureted engines made by Holley. The readings now are around 9 cruising around and at WOT drops to 7. The first gauge was a generic one for a fuel injected engine. I'm wondering if it's supposed to drop 2 psi during WOT.
Tim, Since we are in the Q-jet forum, we should be talking about a Q-jet, right? If your fuel pressure really was 9 psi with a Q-jet, it would be flooding. The Q-jet wants no more than 6. And yes, at WOT, it should drop some. It shouldn't go below 4 psi though.
"If your fuel pressure really was 9 psi with a Q-jet, it would be flooding." Not necessarily. The later units will easily take 7-8psi with .135" seat. Many late model factory fuel pumps put out more pressure than that, and those carburetors had a pretty low float setting to compensate. I would imagine they were trying to circulate a lot of fuel back to the tank as most cars/trucks were A/C equipped in the later years. Absolute max pressure on an early model (68 or older) is 6psi, and they are marginal at that pressure with large fuel inlet seats. I've done some extensive testing in that area with early and late carburetors, with fuel inlet seat sizes from .125" to .149". I run 7psi at the track on my 1977 Pontiac q-jet, never once had the first issue with flooding or fuel control. I have one customer running a mid 9 second Super Stock Camaro that runs 10-11psi and a .125" seat. He claims the smaller seat and higher fuel pressures keep the A/F more consistent on the run. The early units gave the Q-jet a bad reputation for not wanting much pressure, and sucking the bowl dry. The early models simply have a piss-poor hinge pin location, requiring a HUGE float for effective fuel control. The Oldsmobile crowd hates me for pointing this out, as Old's q-jets continued to use that design till 1974, for some reason we will never know?.....Cliff
