When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Swapped out a tired L-48 350 in my 77 vette for a professionally built 350 with edelbrock intake & a holley blaster 650 carb. Now having an issue with excessive heat in engine compartment causing vapor lock. Everything I've been seeing talks of using spacer between carb & intake or switching to electric fuel pump. No room for spacer using my current L-48 hood. Am thinking I might try an L-82 hood or something similar to try to increase air flow out of engine compartment before going the electric fuel pump route. Any thoughts? What year hoods bolt right up to my 1977?
From: At my Bar drinking and wrenching in Lafayette Colorado
You are not experiencing vapor lock.
Vapor lock occurs on the suction side of the mechanical pump when the fuel in the suction line between the fuel tank and the pump is heated on a hot day and then subjected to low pressure from the "suction" action of the pump. This causes the fuel in the suction line to start vaporizing. When a diaphragm pump gets a "slug" of vapor from the vaporized fuel in the pump inlet line, fuel pressure immediately drops to "0" and the car will fall on its face and stall, if under power.
Vapor lock does not occur on the pressure side of the fuel pump, and a hot engine compartment will not cause "vapor lock". On the other hand, the Holley-style carbs are very prone to fuel boiling in the float bowls and in the accel pump well due to the "overhang" of the bowl over the hot engine/intake manifold. This boiling is not caused by conductive heating or convection (remember your 5th grade science class about the 3 forms of heat and energy transfer..?), so using a spacer or insulation on the fuel line will have no effect. The problem is caused by radiant heat transfer into the bowl and into the accelerator pump well. You fix that by installing a reflective heat shield between the primary side bowl & accel pump and the engine, as GM ended up doing on their Holley-equipped engines for this specific reason.
For more info, e-mail me for my "Hot Fuel Problems on Holley Carbs" tech paper.
The L48 and L82 hoods are identical, but your 1977 has a long style, post 72’ hood since it doesn’t have the wiper door. Any 73’-82’ hood will bolt up, although if you’re looking for more hood clearance I would look into an aftermarket L88 style.
1977 corvettes came with a single snorkel air cleaner that allows the engine to take in the cold air from in front of the radiator rather than hot engine bay air. Does your car still have this? If that isn’t sufficient volume some people have swapped it out for the later style, dual snorkel ones. There are people on here as well that run an open element air cleaner, but have shielding built in around it or in the hood, allowing them to run a cowl induction setup.
Insulating your fuel line should help some, but another thing that can greatly affect under hood temperatures is your ignition timing. What is yours set to?
From: At my Bar drinking and wrenching in Lafayette Colorado
You are not experiencing vapor lock.
Vapor lock occurs on the suction side of the mechanical pump when the fuel in the suction line between the fuel tank and the pump is heated on a hot day and then subjected to low pressure from the "suction" action of the pump. This causes the fuel in the suction line to start vaporizing. When a diaphragm pump gets a "slug" of vapor from the vaporized fuel in the pump inlet line, fuel pressure immediately drops to "0" and the car will fall on its face and stall, if under power.
Vapor lock does not occur on the pressure side of the fuel pump, and a hot engine compartment will not cause "vapor lock". On the other hand, the Holley-style carbs are very prone to fuel boiling in the float bowls and in the accel pump well due to the "overhang" of the bowl over the hot engine/intake manifold. This boiling is not caused by conductive heating or convection (remember your 5th grade science class about the 3 forms of heat and energy transfer..?), so using a spacer or insulation on the fuel line will have no effect. The problem is caused by radiant heat transfer into the bowl and into the accelerator pump well. You fix that by installing a reflective heat shield between the primary side bowl & accel pump and the engine, as GM ended up doing on their Holley-equipped engines for this specific reason.
For more info, e-mail me for my "Hot Fuel Problems on Holley Carbs" tech paper.
This is a reproduction GM heat shield for a Quadrajet. They stamp the GM part number 3969837. The NOS originals are rather pricey but I found this one online at The Parts Place. It had to be trimmed/bent in a few places to suit my application but it should work well to prevent fuel percolation. Had to trim out for the vacuum fitting port. Some slight bends here and there but it was easy.
From: At my Bar drinking and wrenching in Lafayette Colorado
Keep in mind the OP does not have a Q-Jet - he has a Holley. A properly fitted Holley reflective shield looks like this:
(Demon carb shown - Holley is the same configuration)
This shield reflects heat away from the bottom of the float bowls, and keeps the heat reflected away from the accelerator pump well, which is the critical component when the fuel starts percolating in the Holley carb.
Lars
Lars: Hmmmm… If I have an original winters intake (1971 LT1), but an Edelbrock carb (1405). I take it the Holley version would be best? What about running one of those shields AND a 1/4” phenolic as well. I ask only as I tend to want to overkill when I can to just make sure. What say you good sir?
Last edited by litevette; Oct 24, 2024 at 06:32 PM.
From: At my Bar drinking and wrenching in Lafayette Colorado
Those old Carter AFB carbs are not prone to fuel percolation in the carb bowl, and you do not need to run a shield. As noted earlier, bowl and accel pump fuel percolation is not caused by conductive heating - the standard carb base gasket provides plenty of thermal barrier to prevent excessive heat conduction, so a 1/4" phenolic spacer is completely unnecessary to prevent radiant heating into the carb.
Good to know about the spacer not being needed as space is limited (hood clearance). You mentioned the Carter carb not being prone, would you say an Edelbrock 1405 is/is not prone? Wanting to set it up for success from the get go and incorporate what you say is best.
EDIT: Did a lil research. Apparently the Edelbrock’s and those Carter’s have a lot in common. Ok. I guess than answers it. Thanks man! Glad to hear what you said!
From: At my Bar drinking and wrenching in Lafayette Colorado
The so-called "Edelbrock" carbs are nothing more than a re-pop of the old, obsolete Carter AFB carbs from 1964. After they were deemed obsolete by GM after 1966, the have become a "performance carb" after Edelbrock made them shiny. We used to throw them in the trash can in the early '70s. Edelbrock's marketing team is filled with geniuses and pretty girls who can make old junk parts turn into performance parts with the simple passing of a generation and a lapse of memory...
Vapor Lock
