Being a 75, my Corvette has the solenoid operated cowl vent.  A few questions on this:

(Mine had been unplugged and the stock air cleaner had been replaced.) 

I assume this was to direct cold air to the carb.  What controlled the opening of the vent.  I've heard from different sources that it was open under full throttle operation, or opened when the key was on.  Maybe this depended on the year of the car.

These cars get very hot under the hood -- is there any reason that this vent should not be held open all the time?

My '73 operated at full throttle using a kick down switch on the accelerator pedal. And yes it was to allow cold air into the intake. They used a formed rubber gasket on top of the outer air cleaner ring to seal it to the hood. 

1973 L-82 4 spd

It's called reverse cowel induction. Pulls cold air in from the base of the windshield. Directs it to the air cleaner, instead of from under the hood. It's not a vent. As said above, with the air cleaner ring installed and the rubber isolator on it, it pulls cool air from outside the car. 

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If this were held open, do you think it would vent some of the heat from under the hood?  I think the heat killed my Holley EFI. . .

When you are driving, I believe there is a high pressure area at the base of the windshield so air would not be escaping from there.  That's why they put the cowl induction there.  NASCAR race cars take their air in from the windshield base.

I removed the whole mechanism out of the hood years ago. Don’t see what it would hurt. I believe GM only had it open if you held your foot at full throttle to reduce engine noise outside the vehicle.

Brian - NCM Lifetime Member

73 coupe L48, Flat-top pistons, Performer RPM Heads, Crane Cam and roller rockers, Holley 650 vac sec. Performer intake,
3.55 gear BTO 200-4R trans,
Leather seats, Seatbelt Plus 3point seatbelts, Pioneer CD player
Magnaflow Exhuast System

Not sure if it would cook a EFI unit, but check to see if all air dams under the car are intact, the foam fillers around the radiator are in and the filler on top of the radiator support is there, and the vents behind the front wheels are not restricted. Forced cool air through the radiator Could mean less heat in the engine compartment. The vent behind the front wheels may help dissipate heat as well. Is the fan clutch operating well?  Is the fan schroud intact? 

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Years ago, my uncle(an engineer at Vought/LTV Aeronautics) did wind tunnel testing on the L-88 cowl hoods. He told me that at speed, that area is actually in a slight negative pressure. So the cowl hood design does not technically force air into the air cleaner. It does, however, allow cooler outside air into the air cleaner assembly, without that intake air being blasted by the extreme heat from the engine/radiator, since the air cleaner base was sealed to the hood. Without the sealed air cleaner assembly, the cowl hood flapper is basically useless, but with it removed or set full open, it would certainly give hot air another escape path....right into the cabin vent system. So....hot air coming out of the cowl hood opening is pulled right into the interior of the car....which are hot inside to begin with. This is the reason Corvette hoods have that rubber seal running across the rear...the help keep the hot air out of the cabin.

If you feel that the heat from the engine compartment contributed to the demise of your EFI unit, I would suggest possibly making the cowl hood system functional by sealing the air cleaner base to the hood.

Joel Adams
C3VR Lifetime Member #56    
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As mentioned above getting airflow into, and through, the engine compartment from the front of the car is key to keeping things cooler overall.  Followup what on what was said about making sure the air dam below the chin is in place to direct air up into the radiator otherwise air passing below the car will just stay there.  And make sure the fan shroud is tight to the radiator to help direct as much air as possible through the radiator, not sneak around it, to cool down the engine.  Ducting extra air from below the bumper directly into the engine compartment will help also.  Just don't take too much so the flow through the radiator is diminished.

A lower temperature thermostat will let the radiator begin cooling sooner.  For the most part an engine will find its own operating temperature regardless of what temp the thermostat is, the lower temp thermostat just lets the cooling happen earlier.  Adding electric fans will help keep constant airflow into the engine compartment and force air out.

Getting hot air out of the engine compartment is the trick as hot air rises and gets trapped under the hood.  A majority of front engine cars are designed so the engine compartment air exits below the firewall and under the car.  The gills/grilles/vents on the C3 front fenders are mounted low, which isn't optimum imho, but they do allow an exit point for some of the hot air which is a bit higher than flowing under the firewall so as was mentioned make sure they are not blocked off.

Also as was mentioned above having the seal between the firewall and hood in place will keep hot air from the engine compartment from being pulled into the cabin venting.  And the cowl vent in the hood, wherever it is placed, is to get cooler outside air into the air cleaner/intake, it's not designed to be an exit point for air from the engine compartment.

Jim Olson 

"The Toys"...!!!  Save the Wave!

Where I've been in a Corvette...!!!

Actually, I replaced the fan with an electric fan a year ago, which with the new shroud fitting tight against the radiator it creates a tight seal.  With the original shroud out, there is a large area for the hot air from the radiator to escape below the engine. The electric fan is controlled by the EFI computer.
This setup seems to work much better than the stock engine-driven fan and keeps the coolant temperature much more controllable.

There is actually a second fan in front of the radiator that comes on when the A/C pressure is high, or when the coolant temperature goes too high, controlled by the EFI computer.  The A/C I put in is from Vintage Air, and it removes the opening from the cowl to inside the cabin, so there is little hot air coming in from the engine area.

It gets so hot under the hood that I can't touch the air cleaner.  The computer for the EFI is inside the throttle body so it also gets quite hot. 

Thanks for all your responses!