Return Fuel Line & Carb Heat Shield by Lars
01-18-2015, 07:03 PM
#41
Burning Brakes
I have to agree with Lars on the return.
The reason GM changed and started putting the regulator at the tank instead of at the fuel rail was for emissions requirements. The flow back to the tank generates more vapor. The rear regulator is not as good for performance applications. In fact there is a TSB (I lost the link) for GM describing that there are more injector problems with no fuel rail return because any buildup in the system (from fuel additives) has no place to go except through the injectors.
The reason GM changed and started putting the regulator at the tank instead of at the fuel rail was for emissions requirements. The flow back to the tank generates more vapor. The rear regulator is not as good for performance applications. In fact there is a TSB (I lost the link) for GM describing that there are more injector problems with no fuel rail return because any buildup in the system (from fuel additives) has no place to go except through the injectors.
01-18-2015, 07:37 PM
#42
The injected cars I have in my garage all have the pressure regulator, and the return line origin, on the engine in the engine compartment, but perhaps the injection comparison was a bad choice, and irrelevant to the conversation in this thread: Injected cars with the pump in the tank don't need to run a return to avoid vapor lock and carb bowl fuel boiling, since the fuel supply line is pressurized to about 45 psi all the way to the injectors - the only purpose of the return is to regulate the pressure, and to prevent the fuel pump from dead-heading, so the return can be placed at any location. You are correct.
That's not the case on a carbureted engine with an engine-driven fuel pump. To avoid vapor lock, the fuel return must come all the way from the fuel pump, which is located in the engine compartment. And to avoid heat saturation of the fuel in the line between the pump and the carb, and to reduce in-carb fuel boiling, the return is always placed as close to the carb as possible on any high performance carbureted application. Take a look at the plumbing system in a NASCAR running in one of the carburetor-mandated classes and any competitive road race car running a carb. On our drag cars, we all run the fuel return over and through the carb float bowls and back to the tank. It's common practice on any high performance application.
Are you suggesting that a fuel return line not be used..? I'd like to see that done on a street-driven car with a carb in hot weather running up a long hill... If you've had luck with that, you're much luckier than me... I install full-length return lines from the engine compartment on every car I build. If I could avoid the time and expense of doing that, I certainly would.
Lars
That's not the case on a carbureted engine with an engine-driven fuel pump. To avoid vapor lock, the fuel return must come all the way from the fuel pump, which is located in the engine compartment. And to avoid heat saturation of the fuel in the line between the pump and the carb, and to reduce in-carb fuel boiling, the return is always placed as close to the carb as possible on any high performance carbureted application. Take a look at the plumbing system in a NASCAR running in one of the carburetor-mandated classes and any competitive road race car running a carb. On our drag cars, we all run the fuel return over and through the carb float bowls and back to the tank. It's common practice on any high performance application.
Are you suggesting that a fuel return line not be used..? I'd like to see that done on a street-driven car with a carb in hot weather running up a long hill... If you've had luck with that, you're much luckier than me... I install full-length return lines from the engine compartment on every car I build. If I could avoid the time and expense of doing that, I certainly would.
Lars
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monstr (06-11-2020)
01-18-2015, 11:47 PM
#44
Tech Contributor
Member Since: Aug 1999
Location: At my Bar drinking and wrenching in Lafayette Colorado
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Yeah... good grief.
For anyone wanting accurate and factual information on constructing a reliable fuel system for high performance carbureted cars, just send me an e-mail.
Lars
(Hey Mike - was that unusual restraint on my part, or what..?)
For anyone wanting accurate and factual information on constructing a reliable fuel system for high performance carbureted cars, just send me an e-mail.
Lars
(Hey Mike - was that unusual restraint on my part, or what..?)
Last edited by lars; 01-18-2015 at 11:55 PM.
01-19-2015, 09:47 AM
#46
01-20-2015, 06:26 PM
#48
Instructor
01-20-2015, 06:40 PM
#49
Instructor
The Vapor Lock problems on this one almost drove Me and GM nuts. GM's complicated "fix" helped but didn't cure it. Finally fixed it with a $10.00 length of -10 braided line slipped over the fuel line to insulate it from exhaust Manifold heat.
01-20-2015, 06:40 PM
#50
i am 81 years old have owned 11 new corvettes and many other HI PERF GM cars,ran a race engine shop that built engines that raced in NASCAR. i was also in the GM pipeline for speed parts that were delivered to my shop directly from GM and Katech at no charge. i could call directly into Chevy performance dept in detroit and get answers and parts from the people there. i am not someone who lives in his parents basement with a computer
01-20-2015, 06:44 PM
#51
Instructor
i am 81 years old have owned 11 new corvettes and many other HI PERF GM cars,ran a race engine shop that built engines that raced in NASCAR. i was also in the GM pipeline for speed parts that were delivered to my shop directly from GM and Katech at no charge. i could call directly into Chevy performance dept in detroit and get answers and parts from the people there. i am not someone who lives in his parents basement with a computer
01-20-2015, 06:55 PM
#52
know all about vapor lock as we had to move the fuel lines outside the frame on our 55 chevys we ran at the 1955 southern 500 in darlington when you ran dual exhaust. you also had to move the brake lines outside the frame because the exhaust heated up those because they were inside the frame from the factory. vapor lock in nothing new
Well, I stayed at a Holiday Inn last night. Does that count?
01-20-2015, 09:09 PM
#55
Instructor
01-21-2015, 10:04 AM
#57
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The 83 would stall in hot summer traffic jams when new....4 barrel 305 5 speed. I always thought it was and air conditioner problem. I think there was a relay to step up the idle speed when ac was on. I plan to plumb a return up close to the carb on both cars this summer.Thanks Lars.
01-21-2015, 01:39 PM
#58
Instructor
The 83 would stall in hot summer traffic jams when new....4 barrel 305 5 speed. I always thought it was and air conditioner problem. I think there was a relay to step up the idle speed when ac was on. I plan to plumb a return up close to the carb on both cars this summer.Thanks Lars.
I found out it didn't work so good when I lost a race a few nights later . Some Kid had Daddys 71 Corvette with the stock 454 in it. ( I once owned a 71 - 454 Corvette for a few Months ...Slowest gas drinking POS ever ) When I challenged Him , He asked what I'm running "stock 305 it's brand new just got it a Month ago" . He thought that was funny , I said when you're done laughing $20.00 says You can't beat it . We lined up and I got Him out of the hole , pulled on him in first hit second and had 2 cars on Him when it fell on its face at the top of second .... I was pissed.
Run a return Line and be sure to insulate the the Fuel line on the frame rail near the right rear exhaust Manifold . As I said in the above post a length of -10 braded stainless hose will work fine . Stan.
