Bypass Fuel Pressure Regulators

Grumpy, do you have any links about modifying the fuel tank pick-up/sender assembly
to work with larger diameter lines? I know I can have a sump added to the tank.
Can the Holley regulator (12-803, I think) be plumbed in reverse for use as a
bypass regulator in the return line? (as in your diagram above)
I am talking about 5-7 psi for carb use.

I will be using a Quadrajet carb. Can I follow this diagram?

I also found these:

I can easily see where the diagram may be confusing ,, and while that cheap holley return style fuel pressure regulator works
at maintaining fuel pressure on the inlet port and can be used its far from the better choice
this is the type of FP regulator you want in most cases,
and it comes in AN#8 and AN#10 sizes

its simply a strait through fuel flow with a pressure release that leads to the return line that opens if the fuel pressure exceeds a set level, thus it maintains that max pressure
https://www.holley.com/products/fue...regulators/carbureted_regulators/parts/12-841

http://documents.holley.com/199r10575rev3.pdf

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

Thanks Grumpy. Do you have any links about modifying the fuel tank pick-up/sender assembly
to work with larger diameter lines? Does anyone make these? If I manage to get the small old
lines out, what do I use to seal and hold the new larger lines in place? JB Weld maybe?

when Ive done that in the past I simply used 1/2"| stainless tube ,drilled out the fuel tank plate insert like you pictured above, bent it to match the required location & clearances and had them tig weldeded or BRAZED by a buddy of mine who does excellent quality tig welds., or I'd braze them

http://secure.chassisshop.com/partlist/6336/

http://garage.grumpysperformance.com/index.php?threads/bending-fuel-line.1660/#post-4554

I didn't know you could braze stainless.
But I have a buddy who is an FAA welder for Pratt & Whitney and
he can weld circles around most other welders.

I like your idea and I will try to make the lines out of the sending unit
longer so that the connections can be made further out past the tank
itself where I can easily get to them later, instead of on top of the tank.
Unfortunately, I read that I have to drop the rear axle to remove the tank.

Since I have to go through all this work anyways, should I just have Kevin weld in a sump?
Got any links on doing that?
That way I can keep the charcoal canister and vent hooked up to the stock lines in the
sending unit and cap off the supply and return lines. Then the new 1/2" supply and return
lines can connect to the sump.

there's also , several other ways to connect larger fuel tank pick-up and return lines

http://garage.grumpysperformance.com/index.php?threads/installing-a-fuel-cell.733/#post-6470

http://garage.grumpysperformance.co...-sizing-return-vs-feed.3067/page-3#post-61157

http://garage.grumpysperformance.co...c-fuel-pump-selection.10664/page-3#post-47899

http://garage.grumpysperformance.co...-big-a-fuel-pump-do-you-need.1939/#post-46020

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/#post-23798

I looked at the fuel tank on the 84 TransAm. There is no easy way to add a sump.
The tank fits up into a tight pocket surrounded by the rear frame rails on each side,
the panhard bar and crossmember connecting the frame rails together and rear axle
on the front side, the cargo well at the rear of the tank, and the transverse mounted
muffler on the bottom with a heat shield in between. The tank is boxed-in.

It looks like I have a 3/8" fuel supply line, 5/16" return, a 3/8" vent, and another 5/16"
line to the charcoal canister. Reading through Grumpy's links above, I calculated that
I need 32 GPH at the carb for 400 HP. And a 3/8" fuel supply line is capable of supporting
up to 500 HP.

Question: fuel lines are sized by their OD. So their ID basically measures the next size smaller -
example: a 3/8" OD line has an ID of 5/16". In the chart below, which are we talking about?
If we are talking about OD, then I should be able to supply 400 HP with my factory lines.

The last time the car was running, it was falling flat in 3rd gear during 1/4 mile runs.
First I tried a larger Carter M4891 mechanical fuel pump rated at 120 GPH and 7-8.5 psi,
which forced me to use the deadhead 12-803 Holley regulator to lower the fuel pressure.
It still ran flat in 3rd gear. I think I tried a 14 psi Holley Blue electric near the tank, but it
sounded like a chainsaw, so I said forget that.
I also tried progressively larger needles and seats all the way up to .130". Still no improvement.
My band-aid cure was to add a QUIET 12v solid state electric fuel pump at the back of the car to
give the fuel a push up to the STOCK (40 GPH?) block mounted mechanical fuel pump. The 12S ratings
are 4-7 psi and 35 GPH. It cured the running flat in 3rd gear problem, but soon after I had to park the
car due to engine problems. I also found that if I turned the 12S off that the mechanical would still pull
fuel through it during normal driving. I only had to apply power to it when making full throttle runs.



At that time I completely tested my fuel system for restrictions - the 3/8" metal supply line,
the in-tank screen filter, and even the gas cap. I can't find my old notes, but if I remember correctly,
the 3/8" metal supply line gave a 17 GPH restriction and I inspected every inch of that line
for crushes or kinks. There are none. I also blew compressed air through the line.

Grumpy says, "keep in mind a fuel pressure regulator can only control the pressure between it and its
pressurized feed source, by bleeding off pressure above the peak its set for, it has zero control past it,
it only controls pressure between it and its pressure feed source."

grumpyvette said:

THE DEAD HEAD STYLE REGULATOR... frequently not to be trusted
works with a spring on a valve that allows the valve to open once the DIFFERENCE IN PRESSURE between the sides of the regulator valves fuel lines has changed.
Think of it as a door that usually has 7-10psi on the feed side and you want lets assume 5.5 psi at the carburetor feed,
you'll need to understand that the dead head regulator works on the DIFFERENCE in pressure between the feed and use sides so having 10psi on the feed and 7psi on the use side is almost exactly the same as having 12psi on the feed and 9psi on the use side to that style regulator, it uses a spring and residual fuel pressure to limit flow until the difference in pressure exceeds a set value.
as the fuel pump fills the line it eventually (fractions of a second) reaches the point where there is a volume of fuel past the valve with enough pressure to allow, BOTH the SPRING in the regulators valve and the fuel pressure past the valve to close the valve.... until the fuel pressure past the regulator is reduced to the point that the SPRING and the remaining fuel pressure/volume beyond the valve can not hold the valve closed and the valve is force open and held open until, that difference in pressure is restored. Now lets launch the car hard, the pump that had maintained 8-10 psi to the regulator, 5.5 psi past the valve and the spring in the regulator is now fighting the fuel in the line feeding the regulators inertia, and the sudden drop in pressure as the throttle drops full open in the carb, what the pump sees is the full 8-10 psi or MORE the regulator sees a sudden drop off to near zero and it opens wide, if the fuel pumps able too it tends to flood the fuel bowl for a second then the valve slams shut, until the pressure drops off as you hit each gear the cycle repeats, the result is a surge in pressure and a rapid drop off in volume then a rapid flood of fuel that rapidly cycles as you go down the track.
If you had a accurate fuel pressure sensor at the carb you'll see a rapidly cycling pressure/flow.
If some crud gets stuck in the valve it cant close and your carb FLOODS OUT, because it must
fully close every few fractions of a second to work correctly.

Click to expand...

Today, I took a 12-803 Holley regulator apart to see how it worked and if it would be possible
to use it backwards as a bypass regulator. While it may be possible, what I found inside was a
diaphragm and a spring and check ball. But the orifice the fuel can flow through measures only
7/32" and is obstructed by the check ball on one side and the diaphragm on the other. So the
flow would be even less than the 7/32" hole could possibly pass. Therefore, I will pass on trying
to use this regulator as a bypass regulator.

What I'm hoping will work in the future is to leave the solid state electric FP inline near the tank
and use a larger block mounted mechanical like the Carter M6626 which has ratings of 120 GPH
and 5.5 to 6.5 psi and has a return line. Jegs has it for $19.77.
Then I will not need to add a bypass regulator and it will keep things simpler.
I am not ready to believe that I need to upgrade/replace the entire fuel system just to feed 400 HP.


BTW, what is the purpose for the longer bases on this type of fuel pump?
Their ratings are the same as the pump above. Is it a reservoir?

this may help



http://garage.grumpysperformance.co...-wonder-whats-inside-a-manual-fuel-pump.5365/


https://www.amazon.com/Dewhel-Inline-Cleanable-Universal-Aluminium/dp/B00ZP3IKVS

https://www.knfilters.com/fuelfilter.htm

https://www.aemelectronics.com/prod...ilters/universal-10an-high-volume-fuel-filter

https://www.redhorseperformance.com...MI-bia9PWW4gIV8o5bCh07nANtEAMYAyAAEgKUzPD_BwE

https://conceptzperformance.com/rad...uel-filter-kits-20-02xx-universal_p_26467.php


low pressure electrical fuel pumps are available for carb applications
https://www.holley.com/products/fue...ed_fuel_pumps/carbureted_electric_fuel_pumps/

http://www.jegs.com/c/Fuel-Carbs-Intakes_Electric-Fuel-Pumps/10307/10002/-1

http://www.edelbrock.com/automotive/mc/fuel-pumps/

http://www.mechanicalcaveman.com/best-electric-pump-for-carburetor-fuel-pump-review/

I just saved that diagram. That could come in handy.
I might have to do that if the 5/16" factory return line is restrictive.

So I was reading another link and found this:
Your hand drawing is correct. It's exactly what I found inside.
It gets confusing when you look at your last (black) diagram and compare it to the labeled regulator picture.
The way the regulator is drawn would make almost anyone hook it up as shown.
That is why I took the regulator apart today - to see if it could be used in reverse. It can't.
Do you think you should correct that black diagram to make it less confusing?
Or at least always attach the labeled regulator picture showing how to properly hook up that regulator.
Now it makes sense how it works after looking at the labeled regulator picture.
yeah. a good quality and properly adjusted, adjustable fuel pressure regulator is generally going to potentially provide,
just enough more consistent fuel delivery volume to be worth a few extra hp, but its major benefit is in the fact in many cases,
it can easily result in 30- plus hp over a improperly functioning O.E.M, fp regulator. (not all that rare)
keep in mind theres a huge difference between replacing a fully functional O.E.M. fuel pressure regulator ,
with an aftermarket adjustable regulator ,
which may or may not provide any benefits and replacing,
a mal functional, O.E.M. fuel pressure regulator with an aftermarket adjustable regulator ,
https://www.thedailystar.net/shift/...ure-regulator-will-improve-performance-111412
http://www.ws6.com/mod-7.htm

Dyno Comparisons -- Adjustable Fuel Pressure Regulator Settings





Here, the dyno shows a 16.6 horsepower and 14.6 ft/lbs torque difference between the stock fuel pressure (46psi) and 36psi with the LG Motorsports adjustable regulator. Actually, it was still making more power at 35psi than 36psi, but until I can measure my O2 sensors, I did not want to lean it out any further. The average gain here was 13.9 horsepower and 15.4 ft/lbs torque. Check out the Dynojet Race Routine between the stock and 36psi fuel pressure.

Something new: Dynojet is currently Beta testing their new WinPEP software for the dyno. With this software, they have the ability to graph up to 12 graphs at once. Check out the Dynojet WinPEP Graph of all the power between the stock and 35psi fuel pressures.

NOTE: One thing that I have found after some time with this mod is that the stock computer is quite smart. After lowering fuel pressure to achieve a better air/fuel ratio, the computer sees this at part throttle and adds injector pulsewidth to compensate. Basically, horsepower fell back off to where I started from. While normal trains of thought tell us that since O2 values are not measured during wide open throttle, that fuel pressure should have a long lasting effect here. Actually, it does not. The computer uses the last known long term fuel trim integer at WOT, which is to add fuel since at part throttle it has adjusted for being too lean.
related threads

http://garage.grumpysperformance.co...ss-fuel-pressure-regulators.12776/#post-65998

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

http://garage.grumpysperformance.co...eplacing-a-c-4-fuel-pump.33/page-2#post-75720

http://garage.grumpysperformance.com/index.php?threads/c4-corvettes-fuel-system-info.67/#post-37351

http://garage.grumpysperformance.co...-big-a-fuel-pump-do-you-need.1939/#post-35934

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-drop.10624/#post-45703

http://garage.grumpysperformance.co...l-line-sizing-return-vs-feed.3067/#post-44732

http://garage.grumpysperformance.co...ed-flow-and-its-limitations.11100/#post-49467
your carburetor inlet fuel pressure should be a consistent 5 psi-5.5 psi in most cases, once you get over 6 psi you'll find the carburetor float bowls tend to flood and under 3 psi the carburetor can run lean under hard acceleration.
EFI works at higher pressures

I don't plan on using one of those regulators because of the small .220" passage. Even though it should be connected
as close as possible to the carb, and my Quadrajet carb will have a .130" MAX needle & seat (I don't know what a Holley
carb has, or what their 2 needles & seats would be equivalent to), but for $19.77 I will try that Carter M6626 mechanical
fuel pump first. That might be all I need to do.






for some reason no one reads instructions and thinks the fuel return lines, supposed to be located at the bottom of the regulator and fuel should flow strait thru the regulator from side to side...WRONG! the fuel feeds up from the bottom center, and for some reason i always seem to get more consistent results with the lines hooked up as posted in the picture
BE AWARE THE FUEL PRESSURE REGULATOR MUST BE HOOKED TO AN UNRESTRICTED FLOW RETURN LINE BACK TO THE TANK TO ALLOW THE FUEL PRESSURE REGULATOR TO FUNCTION AND YOU MUST VERIFY THAT RETURN LINE IS UNRESTRICTED, IF THE RETURN LINES BLOCKED THE REGULATOR WON,T FUNCTION, BUT THE FUEL PRESSURE GAUGE MUST BE ON THE SAME SIDE OF THE FUEL PRESSURE REGULATOR THAT FEEDS THE CARBURETOR, the FEED FROM THE FUEL PUMP FEEDS THE LOWER CENTER PORT, THE LEFT SIDE IN THIS DIAGRAM FLOWS UNRESTRICTED BACK TO THE FUEL TANK, THE RIGHT SIDE FEEDS THE CARB AND FUEL PRESSURE GAUGE