Mechanical Fuel Pump for Drag Race

[Tom68]

The combined flow area of TWO standard .110" holley needle seats is equal to a ID of 5/32". Why would you need much more fuel line/fuel fitting ID minimun size than ¼"…? A 3/8" ID fuel line is a 7/16" diameter tube OD.

Length of restriction.

https://sciencing.com/flow-rate-vs-pipe ... 70380.html

[F-BIRD'88]

I have a old NASCAR mechanical fuel pump I should show you. I guess this thing moves the fuel volume pretty good. I will get a picture of it.

Here ya go
Carter with the higher pressure spring, late 90's -10 in - 8 out. This is an earlier one -8 in. We could eventually get them with big enough ports so we didn't have to weld the fittings on. There was no tricks inside, and no need for a regulator. Last car I was involved with was 666hp unleaded 9.5:1. We were making more earlier with Unocal Nascar fuel and no comp limit.

20220830_064709.jpg


Edit, still got a couple, when we switched to unleaded the pumps got unreliable, Goss gave me some replacement valves to try but I never got around to it.

Fuel Pumps.JPG

This is the one I have,
20200228_124710.jpg

If that the mechanical fuel pump that ate the cam lobe on your camshaft?

[F-BIRD'88]

The combined flow area of TWO standard .110" holley needle seats is equal to a ID of 5/32". Why would you need much more fuel line/fuel fitting ID minimun size than ¼"…? A 3/8" ID fuel line is a 7/16" diameter tube OD.

Length of restriction.

The ID of the lines and fittings are WaY oversize VS the flow area of the needle seats on the carb..
The total length is not long enough to be a factor.
Even under G force of acceleration of this car over ¼ mile. But Heat soak of the pump and feed side fuel line can be a BIG factor.

[Tom68]

The combined flow area of TWO standard .110" holley needle seats is equal to a ID of 5/32". Why would you need much more fuel line/fuel fitting ID minimun size than ¼"…? A 3/8" ID fuel line is a 7/16" diameter tube OD.

Length of restriction.

The ID of the lines and fittings are WaY oversize VS the flow area of the needle seats on the carb..
The total length is not long enough to be a factor.
Even under G force of acceleration of this car over ¼ mile. But Heat soak of the pump and feed side fuel line can be a BIG factor.

Heat soak for sure, I've owned two English built carb'd cars (I'm in OZ) both had vapor lock problems, one was fixed by diverting cold air to the fuel pump, the other was fixed by shielding the fuel pump from the hot radiator air (simple s/s shield).

The odd one was, one of them wouldn't go over 55mph in the hills on a cold morning, pulled over, removed air cleaner, Ice all over the jet in the Solex (edit, maybe that was a Zenith) Carby's booster, thought Pommy cars would have been setup to run on cold days.

[F-BIRD'88]

The combined flow area of TWO standard .110" holley needle seats is equal to a ID of 5/32". Why would you need much more fuel line/fuel fitting ID minimun size than ¼"…? A 3/8" ID fuel line is a 7/16" diameter tube OD.

Length of restriction.

https://sciencing.com/flow-rate-vs-pipe ... 70380.html

This is NOT a "constant pressure" system.
Its relative low pressure ,small pipe sizes and short total system length.
Might be 10ft total length.. Cutting the length by 2 will not double the flow rate.
Its not a city water system miles and miles long.

It is flowing thru 2 .110" needle seats. Much smaller combined AREA than the AREA of the smallest part of the feed lines. The length of even the smallest part of the fuel feed lines is maybe 2-3 inches total. All the rest of the (10ft) length is of even bigger pipe. ID. If it was 300 yards long length then the fliw rate might begin to be effected by total system pipe ID Its NOT.

[Tom68]

The combined flow area of TWO standard .110" holley needle seats is equal to a ID of 5/32". Why would you need much more fuel line/fuel fitting ID minimun size than ¼"…? A 3/8" ID fuel line is a 7/16" diameter tube OD.

Length of restriction.

https://sciencing.com/flow-rate-vs-pipe ... 70380.html

This is NOT a "constant pressure" system.

No, it's far worse, it's the line to the pump that will be causing the problem, I've even seen it with rear mounted Dry sump tanks having too small a line to the pump.

We're sort of having two conversations at once, I agree the pressure side (without seeing it) will most probably be fine.

[F-BIRD'88]

Length of restriction.

https://sciencing.com/flow-rate-vs-pipe ... 70380.html

This is NOT a "constant pressure" system.

No, it's far worse, it's the line to the pump that will be causing the problem, I've even seen it with rear mounted Dry sump tanks having too small a line to the pump.

We're sort of having two conversations at once, I agree the pressure side (without seeing it) will most probably be fine.

Its not a Pro Mod.. Its a mid 12 sec car.. Might be making 400 hp.. You can go 10's on this eddy pump thru 3/8" fuel line. But not with over heated boiling fuel in the feed side fuel lines under the car.
Its the excessive heat.

[F-BIRD'88]

On all these GBody GM cars the shape of the gas tank is funky. The factory fuel pickup tube in the gas tank does not extend back far enough and the tank lacks a slosh baffle inside. to prevent all the fuel rushing to the back of the tank under hard acceleration. If the gasoline level is too low in the gas tank the end of fuel line pickup tube becomes uncovered. Does not matter how big the fuel lines are or how big the fuel pump is ,once the pickup is sucking air..

[Callmewaylon]

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

Going to try bypassing it. My pump is only supposed to put out 6psi anyway.

[Callmewaylon]

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.

The only actual rubber I have is from the factory hard line to the fuel pump. The rest is AN line, which is rubber under the braiding but that's what I see everyone running.

[Callmewaylon]

Hey guys, thanks for all the responses. A lot of good ideas that got me thinking. My first step is going to be removing the regulator. Also, I measured the pressure drop making a test hit on my favorite backroad after I installed a temp gauge at the cowl so the fuel lines were less likely to be heat soaked. Don't really notice a lay down on the street, the drag strip is where it always shows up, except when I've raced at night in cooler air. Even though I'm having a pressure drop, I think heat from sitting in the staging lanes is really what's causing the lay down. I'm thinking I need to add a proper return to my fuel sender that deposits the fuel at the bottom of the tank to help keep the fuel cooler thats running through the carb. If that doesn't work, I found a fuel injected sending unit that should go in my stock tank. I can use a TPI fuel pump that I can then regulate down for the carb. I do have an AFR gauge and never noticed it going far from 12.5 at WOT on the strip but it's hard to watch everything. Need to pay more attention next time.

[Tom68]

I do have an AFR gauge and never noticed it going far from 12.5 at WOT on the strip but it's hard to watch everything. Need to pay more attention next time.

Keep your attention on the strip and the other car Wouldn't data logging be nice.

[HQM383]

Hey guys, thanks for all the responses. A lot of good ideas that got me thinking. My first step is going to be removing the regulator. Also, I measured the pressure drop making a test hit on my favorite backroad after I installed a temp gauge at the cowl so the fuel lines were less likely to be heat soaked. Don't really notice a lay down on the street, the drag strip is where it always shows up, except when I've raced at night in cooler air. Even though I'm having a pressure drop, I think heat from sitting in the staging lanes is really what's causing the lay down. I'm thinking I need to add a proper return to my fuel sender that deposits the fuel at the bottom of the tank to help keep the fuel cooler thats running through the carb. If that doesn't work, I found a fuel injected sending unit that should go in my stock tank. I can use a TPI fuel pump that I can then regulate down for the carb. I do have an AFR gauge and never noticed it going far from 12.5 at WOT on the strip but it's hard to watch everything. Need to pay more attention next time.

Can’t see if you mentioned what carb you are using?

Do you have jet extensions?

Are you using a secondary power valve?

Do you have an ignition rev limiter? I’ve had one waaay out to what it was set at.

[F-BIRD'88]

Do not use any type of fuel injection fuel pump.
Just add the Carter P4070 as a Pusher Pump at the back. It pressurizes the feed line to the mech fuel pump.
Re route the gas line. Its too close to the headers, trans or hot exhaust system.
Drop the gas tank and make a new pick up tube for it. ⅜ inch. Use a tube bender.
Thats all you need. + the bypass fuel return line back to the gas tank.
Be sure the Carter pump is getting a full 12v dc power.
use correct wire guage and proper grounding and proper inline fuse.
Best to control the fuel pump power thru a common automotive AC relay to switch it.
Best $57 US you'll spend.. No regulator is needed.

[skinny z]

The combined flow area of TWO standard .110" holley needle seats is equal to a ID of 5/32". Why would you need much more fuel line/fuel fitting ID minimun size than ¼"…? A 3/8" ID fuel line is a 7/16" diameter tube OD.

Length of restriction.

https://sciencing.com/flow-rate-vs-pipe ... 70380.html

Not only length but all of the accumulated bends add up to even further restrictions. Not unlike the exhaust system.
If you were to look at the OEM supply line on my 3rd gen f-body, you'd see the problem. A length of AN line that's more of a straight shot would make a real difference (which is what I did). As for the OP, I think he's addressing the heat issue.