Quote:
Originally Posted by Tom Vaught
Holley pumps for sure need the fuel "by-pass" circuit (LIKE SOME CARTER FUEL PUMPS OFFER), because the moveable vanes move outward,stick, and then block fuel flow. It only takes one or two sticking vanes to restrict the fuel flow to the mechanical fuel pump. Same deal with any pump that uses Vanes that move outward when the pump is on. Even with the vanes retracted, there is a restriction. The BY-PASS CIRCUIT solves that issue. I use bypass valves with a large "sealing ball" to reduce back flow when the electric pump is on.
As was mentioned, you can buy that bypass system with the pump in some carter pump applications. Not sure of their by-pass flow area.
Tom V.
|
I could see that possibility. My mechanical pump draws through my Holley vane pump without issue though. I don't drag race the car but on short bursts of WOT, it doesn't run out of fuel with the mechanical pump alone. I do have a dual bowl Holley carb which could possibly compensate with its larger bowl capacity.
Before I installed the Holley pump, I put a reducer on the inlet side and ran some low pressure compressed air through simulating a stream and really didn't note any difference in flow out of the pump vs the supply. Not entirely scientific but a test at least. I just decided to plumb without the bypass and see. It has worked just fine without the bypass.
Perhaps if I were a drag race and running at sustained WOT on a Qjet with limited inlet needle and bowl capacity, I might notice a difference but the current setup has worked just fine since installed. The recent onset of a vapor lock condition was the first time the car ever stumbled. Todays fuel of course continues to evolve.