Mechanical Fuel Pump for Drag Race

[Callmewaylon]

I'm running a 408sbc in a 1980 Malibu. Car ran 12.7 @ 107 but has a let off in 2nd gear. Felt like I dropped anchor for a bit and then hit 3rd and took back off. I'm running a stock tank and 3/8" lines. All clean and verified - I've had the tank out of it and it's nice and clean. Running an Edelbrock RPM mechanical pump. I ran my fuel pressure gauge up to the cowl with a rubber line, and under hard acceleration and higher rpm the pressure drops to as low as 2.5. I'm hearing that I should go to an electric pump but I'd rather keep a mechanical setup if I can for serviceability and simplicity as the car is street driven a lot. Is there a better mechanical pump I can use? would running a return style regulator and fuel return help? Edelbrock claims the pump is good to 600hp, but I think it's the g forces on the drag strip that are causing the issue. I've tried cracking the gas cap to make sure venting isn't an issue and filled the tank up after the first time it did it with no change. Pic of my current regulator/pump set up.

[steve cowan]

I would not run anything smaller than -8 fuel lines and pickup/outlet.
A return line is a good idea

[bigaldart]

Carter used to make a 110 gph pump for sbc. That may do the trick. Like you say the 600HP figure might apply on a dyno but add the g forces on the strip and you have nowhere near enough volume. Personally I would fit a Holley electric pump and regulator and know I have it covered.

https://www.holley.com/products/fuel_sy ... /12-327-13

Just seen this and they also do a 170+ gph pump.

[jcisworthy]

This company offers some good products

http://www.robbmcperformance.com/products.html

[skinny z]

Your setup and results very much remind me of my own. I found my OEM arrangement, which was a returnless off the shelf mechanical pump, was having vapour lock issues. The fuel line passed directly over the transmission bellhousing and things were super hot I'm sure. Sitting in the lanes undoubtedly brought things to a boil.

Fast forward, towards the end of my testing I was running a 110 GPH Edelbrock pump combined with a carb specific Holley bypass regulator.
Things went really sideways when one afternoon at the strip, the car was nosing over at the top of 2nd gear more than ever. And no recovery except for enough to idle back to the pits.
This is what I found.

IMG_5777.JPG

I gave up after that and went to a Holley blue pump (which while effective, is noisy as hell). I continued to have a fuel starvation issue and I had to add a 3/8" return line to the OEM 3/8" steel hard line otherwise the fuel pressure was all over the map. The 1/4" return line I was using wasn't cutting it.

Short story: Check the stroke on the pump rod with the pump removed to be sure you haven't carved your way in the cam pump eccentric as in the pic above. Get the right regulator (if you haven't already) as I was running the incorrect one for a while.
Make sure you have overkill on the fuel lines. Both supply and return. I run -6 but the suggestion above with -8 is even better.

I have specifics and pump numbers for the Edlebrock as well as the return style Carter pump I experimented with if you're interested.

[skinny z]

By the way which regulator is that?

20220704_212053.jpg

[ClassicComp]

One of those robb mc pickups in the tank and run 1/2” ID alum line fixed my fuel problem.

[F-BIRD'88]

You don't need pressure . You need flow at high rpm WOT. 2.5# is plenty at highest rpm WOT as long as the fuel bowls are not starved.

The inlet side of the mech pump fuel line IS under a partial vacuum (less than ambient ) when the pump is working hardest.
The lower pressure on the inlet side IF exposed to HEAT (exhaust,trans, headers, etc etc will allow easy fuel vapour lock. (lower pressure = lower liquid boiling point.
Higher pressure = a higher liquid boiling point temperature.
Then the mech fuel pump can no longer pump the fuel (thats now vapour in the fuel line)

The fix is move the inlet fuel lines away from heat and insolate it to reduce radiant heat.
Especially during engine hot soak waiting in the staging lanes between rounds.

One popular fix on drag cars (and street strip cars with headers) is to add a "pusher pump" at near the fuel tank to pressurize the inlet fuel line to stop the fuel in the inlet line from boiling easy from heat (headers)
You don't need a lot of pressure to fix this but you do need flow capacity (and some pressure) .. A Carter P4070 or P4594 electric pump (72 gph free flow rated) is a great fix and easy to add on. You can even shut it off during normal street driving.. (or leave it on)
4 to 7 psi static fuel pressure is fine to pressurize that inlet fuel line..
Further on G body Malibus etc that way the gas tank is shaped it is critical where in the tank the end of the fuel pickup tube is located so it always sees fuel during hard acceleration.. I like to flair the end of the fuel pickup tube to max pick up tube flow.

No regulator is required but optionally you can add a return type regulator with a fuel return line back to the gas tank.
This always circulates fuel to and from the carb back to the fuel tank to also help avoid overheated inlets side fuel lines under car.
That fuel return line MUST extend deep into the gas tank so its under the fuel level.. (Avoids agitating fuel and creating tank vapour) (vapourized fuel is VERY DANGEROUS EXPLOSIVE) Liquid fuel is actually difficult to ignition but aggitated vapourized fuel is VERY COMBUSABLE even in the gas tank.

Move the inlet side fuel lines AWAY from HEAT. first.
Yup headers are nasty.

If you correctly rubber isolation mount the Carter vane Electric pumps correctly, they run quiet.

Further on a GM car with mechanical fuel pump the little rubber hose that connects the frame mounted fuel line to the inlet of the mech fuel pump can tend to KINK and COLLAPSE from HEAT and LOWer inlet side fuel line pressure. Be sure you use the correct reinforced fuel line at this critical connection. Avoid heat exposure and tight bend that kinks when hot.

[BTZ201]

I have ran the edelbrock 110gph in the past through 3/8" lines running 12.0 times shifting at 7k. Never had an issue.
It only puts out 6psi, I never ran a regulator because it wasn't needed.
Maybe the regulator is causing a restriction?
Just a thought.

Brent

[Callmewaylon]

By the way which regulator is that?


20220704_212053.jpg

It's from Summit

[F-BIRD'88]

Further mechanical fuel pump HEAT management..
Seals-IT sells a Heat isolation gasket + bolt washer kit for engine mounted mechanical fuel pumps.
It helps stop the engine block and hot oil from heating up the mech fuel pump so much..
The OEM high perf GM engines back in the day ALL came with a similar purpose fuel pump heat isolation gasket.. People would throw this away then wonder why they now suddenly have hot soak vapour lock on their 396-454 Chevelle. Only GM parts dealers sold replacements..
Critical fuel pump install part.

www.seals-it.com
https://sealsit.com/wp-content/uploads/ ... 088314.png

[F-BIRD'88]

In your pictures all that rubber fuel hose and the regulator itself positioned near the HoT exhaust headers IS a FIRE waiting to happen..
Wonder you got thru safety tech inspection at the track with all that rubber hose..
NHRA says max 12" TOTAL combined rubber hose length on the whole car fuel system.
That is a disaster waiting to happen.
Correct the fuel line route ing and loose 80% of that rubber hose.

[F-BIRD'88]

Another cause of the infamous top of first or top of send gear engine bog is just HoT fuel in the fuel lines caused by HEAT SOAK while sitting in the staging lanes between rounds... Even the pavement is steamin hot. heats up the underside of the csr.
One fix to avoid this is to purge all that HOT fuel sitting in the fuel lines.. On start up, do not just let the engine idle slow.. But run the engine at 2000 - 2500 rpm long enough to now consume all that nasty hot fuel in the fuel lines and pump.
Run it long enough and its gets replaced by fresh cooler fuel from the tank.. 1 minute 2 minutes what ever it takes. 2000+/- rpm
Taking the car for a short drive also helps air flow around under the car to cool off the heat soaked engine bay and undercarriage. This 2000+ rpm running "fuel system purge". will eliminate that nasty hot engine bog at mid track.. Especially with any blended gasoline with ethanol.
10% etc.
Try this hot soak eliminating engine start up /run procedure ...
The added Carter P4070 or P4594 electric "pusher pumps".. Really work too.

[skinny z]

By the way which regulator is that?


20220704_212053.jpg

I asked because I was running the same regulator which I had assumed to be a by-pass style. Turns out it was designed to feed two carburetors rather than have a return to the tank. I was using it that way but it definitely wasn't right.

While some have run dead headed pumps with success (which is what you're doing with that regulator), the vapour lock issue as discussed is very real. All the efforts in the world aren't going to stop it from happening but the effects can be minimized as mentioned above.

That said, a return line to the tank is the way to go. Sometimes you have to hot lap at the track and don't have time for all the shenanigans prior to the next pass.

[F-BIRD'88]

If your Edelbrock RPM mechanical fuel pump is the street friendly version with 6 PSI +/- static fuel pressure at idle... You DO NOT NEED A FUEL PRESSURE REGULATOR AT ALL. All it does is add inline flow restriction and adds another point to pick up radiated HEAT. If the static fuel pressure is 4 to 8 psi at idle Remove thst regulator.. Its serves no useful purpose.

If when you do add tbe Carter P 4070 "pusher pump" at the back so to pressurize the fuel feed inlet line from tank to mechanical fuel pump you still Do not need a fuel pressure regulator at all. As long as the static fuel pressure is 9 psi or less at idle no added fuel pressure regulation is needed. 5 to 8 psi is just right for a holley carb. Edelbrick carbs want 5 to 6 psi but not more.

Sharp right angle fuel fittings MUST BE AVOIDED on the whole fuel system.. Barbed type fuel hose fittings must be drill checked for internal passage diameter ¼" (.250")
is the required minimum. Somw fittings may need drilling. and right angle fuel line plumbing must be Radius type .Again ¼" minimum inside diameter.

Some of the pretty hot rod aftermarket fuel filters are very restrictive. The 3/8" in out common paper element fuel filters are fine.. Not pretty but they work.