Starving a 540 Big Block
Thread Starter
Pro
Joined: Nov 2004
Posts: 659
Likes: 0
From: Flower Mound Texas
Starving a 540 Big Block
We're installing a 540 in my Vette and we're scratching our heads about whether or not we should run a 1/2 inch fuel line. Right now I've got the factory 3/8 inch steel line to the carb and a 1/4 inch steel return. We're going to install a Mallory Comp Series electric pump. All indications are the existing lines will not starve the motor, which has been dyno'd at right around 500 RWHP in a previous car.
We'd like to run a 1/2 inch line and use the 3/8 line for the return, but I am not prepared to do a body off to do this. Has anybody done this before with the body on? Is there a flexible fuel line product that's not too wide to run along the crevices atop the frame on the passenger side? This is for a 75 Vette.
We'd like to run a 1/2 inch line and use the 3/8 line for the return, but I am not prepared to do a body off to do this. Has anybody done this before with the body on? Is there a flexible fuel line product that's not too wide to run along the crevices atop the frame on the passenger side? This is for a 75 Vette.
Thread Starter
Pro
Joined: Nov 2004
Posts: 659
Likes: 0
From: Flower Mound Texas
Beneath the passenger door on top of the frame, there is a triangle shaped opening to route the hose through and I do not think a braided 1/2 inch hose can be threaded through it. Admittedly, I do not know for sure...
Race Director
Joined: Feb 1999
Posts: 19,659
Likes: 34
From: Lenoir City Tennessee
Ci 6, 8 & 10 Veteran
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15
One of my buddies is in the process of installing the same setup as you and is thinking this is the way to go also. I don't think he has done the run just yet though. Maybe he will see this thread and comment on his idea.
Instructor
Joined: Jul 2002
Posts: 236
Likes: 0
From: Jacksonville FL
Originally Posted by Razorhorn
We're installing a 540 in my Vette and we're scratching our heads about whether or not we should run a 1/2 inch fuel line. Right now I've got the factory 3/8 inch steel line to the carb and a 1/4 inch steel return. We're going to install a Mallory Comp Series electric pump. All indications are the existing lines will not starve the motor, which has been dyno'd at right around 500 RWHP in a previous car.
We'd like to run a 1/2 inch line and use the 3/8 line for the return, but I am not prepared to do a body off to do this. Has anybody done this before with the body on? Is there a flexible fuel line product that's not too wide to run along the crevices atop the frame on the passenger side? This is for a 75 Vette.
We'd like to run a 1/2 inch line and use the 3/8 line for the return, but I am not prepared to do a body off to do this. Has anybody done this before with the body on? Is there a flexible fuel line product that's not too wide to run along the crevices atop the frame on the passenger side? This is for a 75 Vette.
What condition is your tank in? I'm going to take the opputunity to upgrade to a Fuel Safe fuel cell. I won't have any fit problems because I'm getting rid of the spare tire carrier and I'm going with sidepipes. Fuel Safe does make a Corvette-specific fuel cell, but it is really expensive.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Why do you need a return line? I run a rigid 1/2 inch stainless line with twin electric pumps at the tank and a good regulater at the motor. Why return fuel to the tank with an electric pump. Vapor lock is not a problem with pusher pumps.
Drifting
Joined: Dec 2004
Posts: 1,321
Likes: 0
From: Edgewater (20 miles south of Daytona) Florida
Is There Some Reason You Don't Want To Run A Steel Braided Line Along The Inside Frame Rail/ Add A Couple Of Hose Clams Attached To The Frame And It Will Be Safe And Easy. Dash 6 Line Should Be Used. Buy The Length Of Hose Needed, The Two Ends, Screw It Together And Be Done And Safe. Indeed Use The 3/8 Line For A Return. That's The Best Set Up.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
Originally Posted by Fevre
And lower hp non-ac cars too. 
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Originally Posted by Ironcross
I dont recall non AC cars with a return line, give me a few and I`ll look it up. But high HP solid lifter engines dont have return lines except injected and supercharged.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
Originally Posted by Fevre
My 73 vert has a return line an no evidence of A/C.
Drifting
Joined: Dec 2004
Posts: 1,321
Likes: 0
From: Edgewater (20 miles south of Daytona) Florida
Wrong
Originally Posted by Ironcross
3/8 line is adequate, no need to change. Return lines were used on lower HP AC cars.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by Glenn"Mr.Blue"Smith
The need for a return line in a PERFORMANCE vehicle is different than a stock one. It was done for emissions on the vette, but for performance, it's done to run better pressures with out blowing the needle and seat out. It ensures a full supply to the bowels at all times, and no more. Do the return line. BG suggests even a LARGER return line. Check into it and you'll find this is good advise.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
Originally Posted by norvalwilhelm
I monitor fuel pressure from the pumps to the regulator mounted very close to the carbs and I get 16 pounds. A high quality regulator with 4 outlet ports feed the 4 float bowls 6 pounds of pressure. How will a return line improve my pressure to the carbs and prevent blowing the needle and seat when all the carb sees is 6 pounds?????
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Originally Posted by norvalwilhelm
I monitor fuel pressure from the pumps to the regulator mounted very close to the carbs and I get 16 pounds. A high quality regulator with 4 outlet ports feed the 4 float bowls 6 pounds of pressure. How will a return line improve my pressure to the carbs and prevent blowing the needle and seat when all the carb sees is 6 pounds?????
Compare this to a return system. This allows the pumps to pump the full volume even at idle. Any unused fuel is returned to the tank. The pumps draw much less current and also receive much better cooling as they are cooled by the fuel they pump.
Running an electric pump dead-head might work (atleast for a while) but it's not the correct way to do it.
Someone might have noticed there is no return line on the new LS1's but they still have a return except it's inside the tank. They then use higher pressure (58 PSI) to the engine to avoid boiling fuel.
Burning Brakes
Joined: Nov 2004
Posts: 899
Likes: 1
From: Kansas
I run a Holley blue pump close to the tank and regulator close to carb and also a pressure guage at carb,when cold the psi is 6.5 ,after running around town in 85 -90 degree temps I check my pressure guage and it reads 0 psi and the pump is still working, So I hooked my old return line back up after the carb and it helped sum , the temps under the hood I believe is what causes my fuel pressure to drop even with a return line ,but when the temp is 50 no problem,I guess no vapor lock in cool climates,
But with the return line I bumped the psi to 8 when cold and after shes hot I have 6psi,I do want to fix this someday so i can run some nitros.
But with the return line I bumped the psi to 8 when cold and after shes hot I have 6psi,I do want to fix this someday so i can run some nitros.
Burning Brakes
Joined: Feb 2004
Posts: 958
Likes: 0
From: shawnee ks
Originally Posted by zwede
Norval: You're being very mean to your pumps. If you think about it, what happens if you prevent an electric motor from spinning? It will draw a bunch of current and get real hot. That's what you're doing to your pumps. They want to pump an enormous volume of fuel but the regulator dead heads and only allows them to deliver a fraction of the designed volume except at WOT. So the pumps are being highly stressed (electrically and thermally).
Compare this to a return system. This allows the pumps to pump the full volume even at idle. Any unused fuel is returned to the tank. The pumps draw much less current and also receive much better cooling as they are cooled by the fuel they pump.
Running an electric pump dead-head might work (atleast for a while) but it's not the correct way to do it.
Someone might have noticed there is no return line on the new LS1's but they still have a return except it's inside the tank. They then use higher pressure (58 PSI) to the engine to avoid boiling fuel.
Compare this to a return system. This allows the pumps to pump the full volume even at idle. Any unused fuel is returned to the tank. The pumps draw much less current and also receive much better cooling as they are cooled by the fuel they pump.
Running an electric pump dead-head might work (atleast for a while) but it's not the correct way to do it.
Someone might have noticed there is no return line on the new LS1's but they still have a return except it's inside the tank. They then use higher pressure (58 PSI) to the engine to avoid boiling fuel.
that runs a return right off the pump which allows you to not have to run a return from the regulator.
Drifting
Joined: Jun 2002
Posts: 1,620
Likes: 7
From: Orlando Florida
Originally Posted by norvalwilhelm
Why do you need a return line? I run a rigid 1/2 inch stainless line with twin electric pumps at the tank and a good regulater at the motor. Why return fuel to the tank with an electric pump. Vapor lock is not a problem with pusher pumps.