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I'm installing a 9 psi heavy duty electric fuel pump at the tank on my basketcase restomod project since the aftermarket/unknown age mechanical fuel pump is failing....and I need to do away with the Bubba rubber hose routing from the mech. pump to the carb
.
Does anyone have an approximate figure of what the pressure at the carb would be....as I am trying to decide on the size of orifice that I would need to feed the return line to the gas tank.
Thanks for any input.
Last edited by doorgunner; 08-31-2015 at 12:03 AM.
For a quadrajet don't you need about 6 psi at the carb?
The previous owner installed a #1405 Edelbrock 600 cfm carb which needs 5-6 psi to operate properly.
I'm installing the 9 psi electric pump on the lower side of the gas tank.
I was wondering if the fuel pressure would drop from 9 psi down to 6psi by the time the fuel reached the carb?
I guess I'll install a T-fitting with a pressure port so I can get a reading with my fuelpressure gauge to make sure the carb isn't getting too much fuel pressure.
I'm going to PepBoys now for the fittings and steel lines.
A bit confused here...a return line is not needed to reduce pressure. A adjustable fuel pressure regulator is. The line or fittings by itself will not do this.
A return line serves to reduce fuel vapor lock and fuel boiling problems.
A "normal" (not race) elec fuel pump puts out 5-6 psi and does not need a regulator.
I am thinking that no one knows what pressure drop you will have - unless it is measured by you. The orifice bleed return may have no effect on pressure, because the volume of the pump may compensate - or it may drop the pressure some -hard to say. If it is a 9psi pump, I would use a regulator at the carb with a return off of it - but other ways will work.
A bit confused here...a return line is not needed to reduce pressure. A adjustable fuel pressure regulator is. The line or fittings by itself will not do this.
A return line serves to reduce fuel vapor lock and fuel boiling problems.
A "normal" (not race) elec fuel pump puts out 5-6 psi and does not need a regulator.
I looked at all the "on the shelf" 5-6 psi electric fuel pumps available locally....they would have been much easier to install, but I wanted a pump that would last for 15-20 years.
The only long-lasting electric pump I could get fast/locally over-the-counter was a 9 psi pump with a lifetime warranty.
I will put a fuel-bleed-orifice in the return line where it T-s off from the carb inlet to reduce the fuel pressure to 5-6 psi/no need for a bulky regulator at the carb inlet....and at the same time let the orifice return fuel through the return line to the gas tank (a "2 for 1" modification).
The original return line from the mechanical fuel pump was rusted/leaking along the frame. I am installing a temporary return line because of fuel boiling in the carb with 150-200*F fuel line temps between the fuel pump and the carb. When I lift the body this winter to replace the body mounts/bushings, I will install the return line in it's correct location.
I do not want a return line exiting at a replacement mechanical fuel pump, as there are approx. 20 more inches of pressure line between the fuel pump and the carb that will be heated to 150*F or more.
Sure...the re-routing is unusual--but other members have done it... the car is a resto-mod, and I'm making necessary changes to eliminate as much fuel-heat problems as possible.
I was wondering about the drop in fuel pressure (if any) from the electric pump at the tank all the way to the carb before a return line was installed.
While I was installing the return line I wanted to install a fuel-bleed-orifice into the return line at the carb to drop the pressure if necessary.
Hmmm.... A pump with a 'lifetime' warranty. That means that, if your pump fails, just return it and you will receive another one JUST LIKE IT. Must be from "The Zone".
More seriously, the Quadra-Jet [and most other regular carbs] will have problems if the fuel pressure is over 5-6 psi. If you have a 9 psi pump, pressure will be well above 5-6 at the carb. You will need a regulator, IMO.
I looked at all the "on the shelf" 5-6 psi electric fuel pumps available locally....they would have been much easier to install, but I wanted a pump that would last for 15-20 years.
Then you should have stuck with a mechanical pump.
I will put a fuel-bleed-orifice in the return line where it T-s off from the carb inlet to reduce the fuel pressure to 5-6 psi/no need for a bulky regulator at the carb inlet....and at the same time let the orifice return fuel through the return line to the gas tank (a "2 for 1" modification).
The problem with using an orifice is while it may work fine at idle, the pressure will drop considerably when the engine is under a load. A regulator would resolve this.
Hmmm.... A pump with a 'lifetime' warranty. That means that, if your pump fails, just return it and you will receive another one JUST LIKE IT. Must be from "The Zone".
More seriously, the Quadra-Jet [and most other regular carbs] will have problems if the fuel pressure is over 5-6 psi. If you have a 9 psi pump, pressure will be well above 5-6 at the carb. You will need a regulator, IMO.
LOL! My '88 ASTRO van was "insured by the ZONE"! I owned it 20 years....the last 17 years-----the ZONE picked up the tab on the replacement parts. Since the Vette is a non-original basketcase, the ZONE will "warranty" all my parts...this allows me to spend the "big bucks on shiny stuff".....
As for a regulator.......When I built my '34 street truck/350 SBC, I used an OEM gas tank which had a 55 psi in-tank pump....I used the same idea to drop the pressure down to 5-6 psi on the 600 cfm Holley carb.....the "system" has worked perfectly for 8 years.
I'll try to install the new pump today/take a pressure reading at the fuel line before I connect it to the carb....and post the results.
(Besides....I'm an ex-Army/doorgunner.....I don't know how to do things the easy way....LOL!)
Last edited by doorgunner; 09-01-2015 at 07:40 AM.
Then you should have stuck with a mechanical pump.
The problem with using an orifice is while it may work fine at idle, the pressure will drop considerably when the engine is under a load. A regulator would resolve this.
Ahhhhhhhhhhh.....a man of few words!
Thanks for the info. I attached a temporary fuel pressure gauge at the carb inlet so that I could see it while test driving the '34 SBC....the gauge never dropped below 5 psi.....maybe it was a fluke?
If this doesn't work correctly today as it did with the '34 SBC, I'll post a pic of the nice shiny return-regulator that you guys talked me into buying.
bashcraft/fellow members.........you guys just made the modification easier by talking me into buying a fuel pressure regulator, rather than fabricating a T-fitting with a return bleed orifice!
You're welcome. I can appreciate a man with an inventive mind and a will to 'experiment'. I can also appreciate a man who finds reason in others' fair counsel.
The regulator supply and return lines are installed......I had to angle the regulator down about 1/2" to clear the air plenum................
It's a close fit/about 1/8" gap b/twn the regulator and the plenum.....I'll put a 1/8" gasket under the plenum later.......
Tomorrow I'll finish running the return line to the gas tank, then run the pump, check the fuel pressure at the carb, adjust the regulator and go for a test drive.
Thanks.......I had to use two brass fittings per connection to connect the test plumbing.....which makes the regulator look bulky.....I'll order the correct stainless single fittings now that I am satisfied with the routing.
I will be posting any additional info in my build thread in the General Forum.
Last edited by doorgunner; 09-02-2015 at 09:08 PM.
I like how you routed that. Now the Nawlins heat will have a harder time getting to your fuel.
It will be impossible now....I also ran it down the passenger firewall as far away from the exhaust manifold as possible....mo more 150 to 180*F plus temperatures on the pump or carb fuel line!
08-30-2015, 11:42 PM
Fuel pressure drop?
