Bypass fuel pressure regulator systems

[Vic Santos]

I really thought hard as to whether to post on this subject but I thought some might be interested in my findings:
During the first 2 to 3 seconds of a run using a Q-Jet, fuel pressure to the carb is never constant no matter what fuel system you have! During launch the Q-Jet inlet valve actually closes multiple times for as much as 1/4 of a second at a time. The reason is the fuel in the bowl is pushed to the back of the bowl (by G force) and that is where the float is. At the same instant the G force acts on the fuel in the line supplying the regulator causing the fuel pressure to the regulator to go down by 5 to 10 psi depending on the G force and the length of the fuel line. At the time the inlet valve closes there is NO FUEL FLOW through the regulator without a bypass. At that instant pressure ratio across the regulator is varying wildly and the regulator mechanism is trying to cope. This does not happen with a Holley, only the Q-Jet due to its small, single bowl and float design.
That being said, will you notice a difference with a bypass? Only if you have a extremely well set up Q-Jet and multiple data logged sensors. The best Q-Jet set up for launch typically is not the best for the rest of the race. A racing Q-Jet setup is always a compromise. You'll have to try it and see. But you should test different setups.
The best thing you can do for a Q-Jet is to make sure your fuel system can refill the bowl as soon as possible and the carb bowl is as large as possible.
BTW the above info is for system that has a regulated bypass from the pump discharge to the tank i.e. a big pump. The pump is putting out constant psi and flow but the carb never sees it until G loads are stabilized.

[Adger Smith]

Very good info Vic. & right on.. I've had a customer or two that we routed a long lead line from the regulator to the Q-Jet. We used the Leave G forces to feed the carb through the line. I had them mount the Regulator way forward and the line runs back to the carb. I also used a .035 secondary bypass from the Regulator output line to the main by pass line( back to tank) this bled all the air out of the regulator to the carb line. I feel it kept air/foam out of the float bowl.
It really works well with Q-jet and 2 bbl carbs that are used on dirt tracks.

[nhramnl]

Thank you very much for the excellent information, Vic. It is almost word-for-word the same information John Rademacher provided when attempting to convince me to buy the Product Engineering bypass regulator kit. At the risk of getting Ed Bigley stirred-up again, I will say that numerous other Q-jet racers have told me (in PMs) about findings very similar to Vic's. The bypass system "stabilizes" fuel pressure, particularly under high G-loads. Now, I will see if such stabilization translates to quicker 60-foot times, more consistent performance and improved ET and MPH. Thank you to all who responded. As I said in an earlier post, I will report my true and actual findings, once I get the car back out.

[1320racer]

Originally Posted by Todd Geisler

My current carb is from Bob Book. He is quite picky about carb and fuel system setup.
When I ordered the carb I asked about the regulator bypass setup. He said if you data log fuel pressure you would certainly see an improved fuel pressure reading. He also stated that on track they never saw any positive gains from the bleed system.
His opinion is if you already have it, use it. Otherwise it's not worth the time/money to purchase and install.

Originally Posted by Ed Wright

1320 is correct. Won't hurt, but won't run any faster unless it had fuel supply issues before changing to the bypass set up.

Originally Posted by Alan Nyhus

When I put the bypass on, the fuel pressure was a bit more stable. Didn't see any performance improvement but the pump is noticeably cooler. .

Originally Posted by Jeff Stout

What I noticed with my fuel pressure gauge is that the pressure stayed the same throughout the run with less needle bounce also. Cant say any ET gain.

it obvious that no matter how many tell you that all you'll see is a lighter wallet, the only opinions you are interested in hearing are those that agree with what you had already decided to do.

Still waiting for somebody that claims via pm to the OP that they have improved their car's performance on the track by just adding this bypass to their regulator, to please enlighten me how a pair of -3 hoses plumbed into a regulator makes additional HP, enough HP to run quicker and faster as evident on the time slip because without it, there is NO quicker 60 foots and ET regardless of what John tells him or you, those without the conviction to post publicly and engage in reasonable dialog stating your OPINION based on your belief and JUSTIFICATION for choosing to spend your $ on a regulator bypass.

[james schaechter]

Dude, you don't get it all. We class racers spen all kinds of money on stuff just for the hell of it. If you are expecting logic, go to the Harvard College website.

(Tongue in cheek). 😄

Originally Posted by 1320racer

it obvious that no matter how many tell you that all you'll see is a lighter wallet, the only opinions you are interested in hearing are those that agree with what you had already decided to do.

Still waiting for somebody that claims via pm to the OP that they have improved their car's performance on the track by just adding this bypass to their regulator, to please enlighten me how a pair of -3 hoses plumbed into a regulator makes additional HP, enough HP to run quicker and faster as evident on the time slip because without it, there is NO quicker 60 foots and ET regardless of what John tells him or you, those without the conviction to post publicly and engage in reasonable dialog stating your OPINION based on your belief and JUSTIFICATION for choosing to spend your $ on a regulator bypass.