How to turn a high pressure in tank pump into a low pressure pump!!

crazypete · 09-27-2002, 09:42 AM

This is for all you guys doing carb conversions who dont feel like chopping up a perfectly good fuel system and spending hundreds of dollars on fuel pumps and regulators.

I'm converting my 91 mustang to carb and I bought a mallory 5 port return style regulator. Well, the 40 psi stock pump was so strong that my fuel pressure guage went offscale even with the regulator turned to maximum resistance. I even popped a fuel line!

This is what to do: Go to radio shack and buy 4 1 ohm wirewound 10 watt resistors (they'll look like little clay bricks). Tie these in series. Go under the seat and cut the lead wire to the fuel pump and put this resistor pack inline. Beautiful! 6 psi exact! 8 psi with 3, 10 psi with 2 and 15 psi with just 1 resistor.

I'm getting a sore shoulder from patting myself on the back.

flyin 5.8 · 09-27-2002, 11:31 AM

The pressure is good but what happened to the volume? If this just slowed the pump down then the volume would drop also. Right?

Do you know if this would work the same on a 4cyl pump? Is there a difference?

Brian

crazypete · 09-27-2002, 05:15 PM

That's an interesting point.....

My car uses a carb, though, so the pump should be easily able to replace the small amount of fuel being drawn off. If not the pressure can be upped to 11 or even 15 psi and turned back to 5-7 psi using a regulator.

The same concept should work with a 4 banger since the operation of the device is the same, but unless you have a 4 cylinder running a carb, there would be no reason to drop the pressure down this much.

flyin 5.8 · 09-28-2002, 10:20 AM

I'm putting a 351 into my '90lx just planning ahead.

I checked with the electrical engineers at work and they said that this would work, for a while. Reducing the voltage to a motor will slow it down (reducing pressure and volume), but it will also reduce the life of the motor quite a bit.

Does anyone make an in tank pump that is 15psi and 100 gph?

If not someone should start, alot of people are doing carb conversions.

crazypete · 09-28-2002, 11:09 AM

Holley makes one. It's 15 psi 110 lph. Its like $160 bucks

jonnyk · 09-28-2002, 12:02 PM

Holley, Carter, Paxton I believe all make low pressure electric pumps, along with I'm sure a bunch of others. Aeromotive maybe too?
An electric motor will live longer at lower speeds, but the volume of the pump will be so drastically reduced compared to the 40+ psi run with fuel injection that it probably wouldn't be feasible. Just get a new pump and the proper regulator.

Barry Jackson · 09-30-2002, 11:10 AM

I am running 351W in 87 Lx with 750 holley. Find an intank pump from an 86 5.0 as it was carb. See if will run enough pressure, right at 7.5 is what you want. Mine would not so I added a holley blue pump mounted where the old fuel filter was. With the regular mounted up front, I can tune it to 7.5 lbs easily. Also using barry grant braded fuel lines and fittings from the regular to the carb.
Good Luck

09-27-2002, 09:42 AM	#1
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	How to turn a high pressure in tank pump into a low pressure pump!! This is for all you guys doing carb conversions who dont feel like chopping up a perfectly good fuel system and spending hundreds of dollars on fuel pumps and regulators. I'm converting my 91 mustang to carb and I bought a mallory 5 port return style regulator. Well, the 40 psi stock pump was so strong that my fuel pressure guage went offscale even with the regulator turned to maximum resistance. I even popped a fuel line! This is what to do: Go to radio shack and buy 4 1 ohm wirewound 10 watt resistors (they'll look like little clay bricks). Tie these in series. Go under the seat and cut the lead wire to the fuel pump and put this resistor pack inline. Beautiful! 6 psi exact! 8 psi with 3, 10 psi with 2 and 15 psi with just 1 resistor. I'm getting a sore shoulder from patting myself on the back.

09-28-2002, 12:02 PM	#6
jonnyk Being stroked is great Join Date: Oct 1998 Location: Alberta, Canada Posts: 772	Holley, Carter, Paxton I believe all make low pressure electric pumps, along with I'm sure a bunch of others. Aeromotive maybe too? An electric motor will live longer at lower speeds, but the volume of the pump will be so drastically reduced compared to the 40+ psi run with fuel injection that it probably wouldn't be feasible. Just get a new pump and the proper regulator. __________________ Novi 2000 now spinning off the snout of the 331... Mods Pics

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09-27-2002, 11:31 AM	#2
flyin 5.8 Registered Member Join Date: Apr 2002 Location: Holland, Michigan Posts: 73	The pressure is good but what happened to the volume? If this just slowed the pump down then the volume would drop also. Right? Do you know if this would work the same on a 4cyl pump? Is there a difference? Brian

09-27-2002, 05:15 PM	#3
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	That's an interesting point..... My car uses a carb, though, so the pump should be easily able to replace the small amount of fuel being drawn off. If not the pressure can be upped to 11 or even 15 psi and turned back to 5-7 psi using a regulator. The same concept should work with a 4 banger since the operation of the device is the same, but unless you have a 4 cylinder running a carb, there would be no reason to drop the pressure down this much.

09-28-2002, 10:20 AM	#4
flyin 5.8 Registered Member Join Date: Apr 2002 Location: Holland, Michigan Posts: 73	I'm putting a 351 into my '90lx just planning ahead. I checked with the electrical engineers at work and they said that this would work, for a while. Reducing the voltage to a motor will slow it down (reducing pressure and volume), but it will also reduce the life of the motor quite a bit. Does anyone make an in tank pump that is 15psi and 100 gph? If not someone should start, alot of people are doing carb conversions.

09-28-2002, 11:09 AM	#5
crazypete Registered Member Join Date: Sep 2002 Location: Boston Posts: 592	Holley makes one. It's 15 psi 110 lph. Its like $160 bucks

09-30-2002, 11:10 AM	#7
Barry Jackson Registered Member Join Date: Oct 1998 Location: Pitts. Pa. USA Posts: 61	I am running 351W in 87 Lx with 750 holley. Find an intank pump from an 86 5.0 as it was carb. See if will run enough pressure, right at 7.5 is what you want. Mine would not so I added a holley blue pump mounted where the old fuel filter was. With the regular mounted up front, I can tune it to 7.5 lbs easily. Also using barry grant braded fuel lines and fittings from the regular to the carb. Good Luck