Help! Identifying a piece on/in the hood

[Thore826]

I was re-attaching the grill to the front of my hood today (near the windshield) and as I was putting in that plastic screen that fits between the fiberglass of the hood and the inside of the hood (guess air box?) I noticed some type of door. It stretches across the middle (rise) of the hood, about 2" tall, and as far as I can see its opened by some small motor. I was thinking its some type of inlet to get the carburetor air (have the air filter with the pan around it, two oval pipes coming out the front, bicycle-tube-like gasket on top. I always thought the gasket served to seal the air intake to the hood (why the two oval pipes are there and opened seems to defeat the purpose)and allow fresh air to be pulled in from the windshield area of the hood (never understood how it would "scoop" air without facing into the wind, but I'm no engineer), but never noticed the door before. Not to mention, I had the wire disconnected thinking it was for the underhood light, so if the door did work off a motor it hasn't been opening since I got the car.

 

[Thore826]

here's a pic

 

[navy2kcoupe]

Maybe Cowl induction??????????
Andy

 

[Ripp 73]

You are correct Andy, that is the cowl induction. It does run off a motor and is supposed to open when you have the throttle at or near WOT. I do not know exactly how it scoops air back into the carb, but that is what it's supposed to do.

I also understand that it will let cool air move across the top of the engine which is always a plus in these engine bays.

Some say it works, others do not. I say, run it however you feel comfortable.

 

[Thore826]

Thanks, I looked up cowl induction online and have a better understanding of it. Now I gotta see if it works, although I can't find any of the parts for it on Ecklers or Corvette Central so guess whatever condition its in is how its staying

 

[Mac]

You are correct Andy, that is the cowl induction. It does run off a motor and is supposed to open when you have the throttle at or near WOT. I do not know exactly how it scoops air back into the carb, but that is what it's supposed to do.

I also understand that it will let cool air move across the top of the engine which is always a plus in these engine bays.

Some say it works, others do not. I say, run it however you feel comfortable.

There's supposed to be a solenoid to flip the little gate open at or near WOT, triggered by a switch by the gas pedal. The base of the windshield is mildly pressurized by air movement as the car goes forward, bringing outside air directly into the air cleaner & carb... but since there's nothing to prevent the air from going out the two snorkels of the air cleaner, it doesn't provide positive pressurization to the carb.

In practical terms, all it does is open a passage to the engine which faces the driver, providing a bit of extra engine noise unfiltered by the firewall. It was, however, a wonderful marketing tool...

-Mac

 

[Vettehead Mikey]

I did an instrumented test of this system late last year to see if it actually works or not. Some of you that frequent 'that other' website might have seen it.

Long story short it does S-F-A except increase noise as Mac suggests. The theory is that cool air will be ducted into the air filter housing when the flapper is open. Cool air = more HP, at the rate of 1% increase for every 11*F decrease in air temp. The biggest decrease I got was 2* and this was by driving the car at 100 mph into the prevailing wind. Driving with the wind got me a big fat 1*

What kills the functionality of the system is the two open snorkels that face forward into the hot engine bay. Much easier to suck air through those than to squeeze it through the narrow channel in the hood.

 

[Mac]

I did an instrumented test of this system late last year to see if it actually works or not. Some of you that frequent 'that other' website might have seen it.

Long story short it does S-F-A except increase noise as Mac suggests. The theory is that cool air will be ducted into the air filter housing when the flapper is open. Cool air = more HP, at the rate of 1% increase for every 11*F decrease in air temp. The biggest decrease I got was 2* and this was by driving the car at 100 mph into the prevailing wind. Driving with the wind got me a big fat 1*

What kills the functionality of the system is the two open snorkels that face forward into the hot engine bay. Much easier to suck air through those than to squeeze it through the narrow channel in the hood.

I wonder how much of a difference it would make if we ducted from the snorkel to exterior intakes? For instance, down by the signal light grills or similar? Mind you... 1% per 11 degrees isn't a lofty goal to chase. :W

-Mac

 

[Thore826]

so this leaves me with three questions...
1) would it be an advantage or disadvantage to leave the flap/door open (if the solenoid isn't opening it), seeing as there is a screen to keep medium/large debris out... I did hear something about water pulled in during rain
2) i heard the later c3's had some type of flex-pipe that attached to those two snorkels that routed somewhere in the front around the radiator or grille to get fresh air... would adding them work if they're pulling air out of the area in front of the radiator, or they'd have to be a "ram-air" setup with the inlet behind the front flasher grilles forcing air in at speed
3) if routing the pipes is too difficult, can the snorkels be blocked off to prevent the intake from pulling in the engine bay air? will the cowl intake provide enough air, given its open all the time?

when I first got the car, I thought the hose to the snorkels had rotted away and looking at the gasket/underhood figured it was some form of reverse intake, but couldn't figure what the openings would be for if there were no hoses hooked to them (seemed to defeat the purpose), but my brother-in-law's '76 just has an air filter w/o the tray with snorkels, and I don't think he has the cowl-induction hood so I don't have a clue what works anymore!
PS Thanks for the responses

 

[Vettehead Mikey]

I can assure that the 'sucking in rain' theory is nothing but more mumbo jumbo voodoo bad science. Newton's first law (law of inertia) applies here, so convincing rain to do a 180 degree turn and get forced/sucked into the duct would defy all logic and physics. Second point is that there really doesn't seem to be much air flow as witnessed by my experiments mentioned above.

The later C3s have a cold air induction set up taking air from in front of the rad, why not have a look at that and see if it can be adapted.

 

[Thore826]

I'm glad you checked out the airflow of that thing, I hate taking the "it's there for a reason" approach. I'm definitely gonna check out the way the later c3's have their intakes set up

 

[JohnZ]

That location (base of the windshield) is valid as a high-pressure area (see photo below of a Sprint Cup car shot last week at Hendrick Motorsports), but on those cars it goes through a sealed duct directly into the air cleaner, with no airflow direction changes, and has nowhere to go except into the carburetor. All Sprint Cup and Nationwide cars are set up exactly the same way.

It loses a lot in translation on the C3 application, but Marketing loved it.

 

[Thore826]

John, looking at that pic, that's the area on the C3 hood where a grill is located, with the intake right inside there. It appears to be a direct line to the air cleaner assembly with the "snorkels", hich I'm sure these cars don't have. Would these "cowl induction" hoods on the C3's be more efficient if there was a good seal between the air cleaner assembly and hood and the snorkels were either sealed or routed to a front intake near the flasher grilles? I mean, if all it is is a way for air to be fed directly into the air cleaner, I find it hard to mess it up; seems to me as lg as it has a clear path and its sealed up well (snorkels and gasket against hood) then it could function better than stock... not high-performance, but better than a cheap marketing ploy/ stock setup.

 

[JohnZ]

Would these "cowl induction" hoods on the C3's be more efficient if there was a good seal between the air cleaner assembly and hood and the snorkels were either sealed or routed to a front intake near the flasher grilles?

It would help if the snorkels were sealed, but in any event, the feature would provide little real-world benefit.

 

[Mac]

It would help if the snorkels were sealed, but in any event, the feature would provide little real-world benefit.

Chasing a 1% performance improvement makes sense for a WOT racing application but not so much in stop & go traffic.

-Mac