Fuel pump without return line
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
Fuel pump without return line
Question for y’all,
I just installed a 125hp nitrous shot on my 75, mild built motor. Makes 276hp at the wheels, so I’m estimating probably 350hp at the crank. Ideally with the NOS it would make 475 crank hp.
However, NOS recommends a fuel pump flow rate of .1gph per hp at 5psi. I currently have the stock fuel pump which is rated at 40gph free flow.
So I bought a carter street super, rated for 120gph between 5.5-7.5psi. Should be more than enough.
I got the fuel pump delivered today and it does not have a return line, just a inlet and outlet.
I don’t have any experience with fuel pumps without return lines. Can I just attach the inlet and outlet lines, and cap the return? Do you need any form of regulator before the carb? It seems to me that the pump will just be dead headed a large portion of the time.
second question, I’ve seen on the forum that some guys run up to 500hp on the stock fuel pump? I still think in my situation a bigger pump is safer. I’d hate to run lean at 5500 rpms with NOS.
thanks
I just installed a 125hp nitrous shot on my 75, mild built motor. Makes 276hp at the wheels, so I’m estimating probably 350hp at the crank. Ideally with the NOS it would make 475 crank hp.
However, NOS recommends a fuel pump flow rate of .1gph per hp at 5psi. I currently have the stock fuel pump which is rated at 40gph free flow.
So I bought a carter street super, rated for 120gph between 5.5-7.5psi. Should be more than enough.
I got the fuel pump delivered today and it does not have a return line, just a inlet and outlet.
I don’t have any experience with fuel pumps without return lines. Can I just attach the inlet and outlet lines, and cap the return? Do you need any form of regulator before the carb? It seems to me that the pump will just be dead headed a large portion of the time.
second question, I’ve seen on the forum that some guys run up to 500hp on the stock fuel pump? I still think in my situation a bigger pump is safer. I’d hate to run lean at 5500 rpms with NOS.
thanks
Melting Slicks
Joined: Nov 2006
Posts: 3,400
Likes: 1,813
From: Apple Valley, MN
You will want to have a return line. With today’s fuel blends, you will want to do everything you can to keep the fuel from boiling (and creating vapor lock) and one of the fundamental solutions is to keep the fuel flowing under the hood.
Race Director
Joined: Mar 2016
Posts: 14,348
Likes: 8,158
From: Napa Valley California
At some point, the prior owner of my 73 bb replaced the fuel pump with a type that did not have any return line port and he capped the return line.
I’ve owner it for six years without an issue.
That being said, when I do my restomod I’ll be putting in a new return line connected to the fuel regulator rather than at the fuel pump.
I’ve owner it for six years without an issue.
That being said, when I do my restomod I’ll be putting in a new return line connected to the fuel regulator rather than at the fuel pump.
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
I don’t think I’ll need a regulator, seeing that I don’t think the pump will exceed 8psi
Race Director
Joined: Mar 2016
Posts: 14,348
Likes: 8,158
From: Napa Valley California
[QUOTE I don’t think I’ll need a regulator, seeing that I don’t think the pump will exceed 8psi[/QUOTE]
Find the spec’s for your carb and find out what the maximum psi it is rated for.
8 psi is a little high and could cause some issues.
My Quick Fuel 850 cfm is rated for no more than 7 psi max and their tech’s suggest 5.5 to 6 psi is perfect.
The best of both worlds would be to install a fuel regulator, gauge and the return line at the carb.
Find the spec’s for your carb and find out what the maximum psi it is rated for.
8 psi is a little high and could cause some issues.
My Quick Fuel 850 cfm is rated for no more than 7 psi max and their tech’s suggest 5.5 to 6 psi is perfect.
The best of both worlds would be to install a fuel regulator, gauge and the return line at the carb.
Last edited by OldCarBum; Aug 31, 2021 at 09:27 PM.
Pro
Joined: Jun 2021
Posts: 505
Likes: 230
I have a carter pump and a 770 Street Avenger without a return, so far no issues with vapor lock. I ran short of AN fittings so I couldn’t plumb my regulator in with a return, so far it’s working fine but I’ll fix it right this winter if the fittings come available.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
I recommend a return regulator tied into the return line to allow proper pressure control and recovery when on and off the button......there will be a significant drop in pressure for an instant and increase when you let off.....the reg will smooth the spike....plus it is easy to plum in to the return line but do it AFTER the supply at the return. A simple $40 Holley return reg is fine.
Jebby
Jebby
Burning Brakes
Joined: Feb 2020
Posts: 904
Likes: 569
From: Central NJ
Yes, you should have a return line and a bypass regulator, I'd put a gauge right on the regulator to make things easy. Besides possible fuel perculation you will likely have residual fuel pressure at the carb when you switch off the engine, this can cause fuel to seep past the float needle. With a return line in place the fuel pressure will drop to zero when you turn off the ignition. Both of these things can end up giving you fuel in your oil over time, hard starting when hot, besides the NOS issue.
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Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
So, Jebby and 1860, y’all are saying I should run a regulator that goes on the output, but has a connection to the existing return line? I just finished the install today, that pump was a pain to install, it’s wider so not a lot of clearance. And I ran a holly regulator on the output, to regulate it to 6ish pounds which is ideal for my edelbrock carb.
sounds like I bought the wrong regulator, I actually didn’t know they made regulators that fed back to a return until just now
sounds like I bought the wrong regulator, I actually didn’t know they made regulators that fed back to a return until just now
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
So, Jebby and 1860, y’all are saying I should run a regulator that goes on the output, but has a connection to the existing return line? I just finished the install today, that pump was a pain to install, it’s wider so not a lot of clearance. And I ran a holly regulator on the output, to regulate it to 6ish pounds which is ideal for my edelbrock carb.
sounds like I bought the wrong regulator, I actually didn’t know they made regulators that fed back to a return until just now
sounds like I bought the wrong regulator, I actually didn’t know they made regulators that fed back to a return until just now
Look it up at Holley’s site and open the instructions for layout.
Jebby
Thread Starter
Burning Brakes
Joined: Dec 2017
Posts: 1,043
Likes: 414
2023 C3 of the Year Finalist - Modified
Figured I’d update everybody, it took a long while for the regulator to get delivered, went with holly 12-887. Just for curiosity, I ran it with the fuel pump just going straight to the carb, return plugged. It was running quite rich, you could smell it, and when it got hot, it was having trouble just idling.
I installed the regulator once it showed up, adjusted it down to 5-5.5 pounds, connected the return. Appreciate the opinions from y’all, like i mentioned, I had no idea they even made regulators with return connection. Works great!
I installed the regulator once it showed up, adjusted it down to 5-5.5 pounds, connected the return. Appreciate the opinions from y’all, like i mentioned, I had no idea they even made regulators with return connection. Works great!