Hood Induction System ?

[CAPNZ]

YEP! More questions. I'm obsessed with this car. I can't sleep if I find a little thing wrong.
Even though this car is MINT it's still 30+ years old.

Question: When I Iooked under the hood I seen two wires running along the underside. A brown & black. I followed them from the top of the hood to the back of the left headlight wire harness. OPPS, someone cut them at one time. Luckily they didn't cut them short so I'll solder and heat shrink them back together.
On the top of the hood the wires go to a housing which contains a solenoid activated flapper type baffel. Now 2 clips had fallen off at some time that holds the baffel to the frame. So I rigged up two clips to replace the missing ones. (I'm thinking this is why someone cut the wires at one time). I checked it with a 12V battery and it functions PERFECT. NOW, what activates this air induction system? Putting the car in gear, temperature, pressure??????

TIA "JEFF"

 

[Mac]

When the gas pedal is at wide open throttle, it presses against a switch which then powers the solenoid, opening the flappers for the induction hood. In many cases, that switch has been removed but take a look, just in case it's still there.

What I can't understand is why the induction would only been needed at WOT? Why not have it available whenever the choke is off?? My solenoid doesn't work but when it does, it's gonna be wired to a switch which I control.

-Mac

ps: here's a good technical link to Tom73's excellent website, http://1973-corvette.com/

 

[lnirenberg]

Does this type of system feed outside air directly to the intake or is it just additional air into the engine compartment somehow related to emissions reduction or what? I have always been curious if our carburated cars would benefit from some of the cold air mods I read about for the newer injected engines.

 

[JohnZ]

It's mostly for marketing reasons. It does allow some cooler air in to the air cleaner (and makes lots of neat noise) at WOT, but not enough to be significant. Assuming 100% of the intake charge is cooled (which it isn't), each ten-degree reduction in intake charge temperature vs. underhood air temperature will theoretically give a 1% power increase.

 

[lnirenberg]

If I believed all the hype in the ads for C5 inductions systems they are the greatest thing since sliced bread. 1% per 10 degrees doesn't sound like much bang for the buck for retrofitting purposes.

 

[Vettehead Mikey]

What I can't understand is why the induction would only been needed at WOT?

As John said, the door is there for whizzbang marketing purposes and not for performance. It does not open at less than WOT to limit the noise coming from the carb venturi. Part throttle Qjet noises are not quite a love song to my ears. :L

 

[Ludigdrums]

I have an '81 with that same hood...but I thought it was only meant for the '82s with the Crossfire engines?

I ended up just removing the assembly because I don't have the computer anymore, the positive wire was already disconnect, and when I connected it, I couldn't tell if/when it was opening anyway. Plus, it seemed to make sense to just leave it open all the time.

I have a Holley with the K&N filter cover thing...so I don't hear any noises or anything from the extra air.

Good luck!

- Jeremy

 

[kiwi vet]

Hey Ludigdrums

Your hood is different (assuming its an 82), as it opens by solenoid at the front.
The 73 opened by solenoid at the rear, from the high pressure point at the base of the screen, similar idea to the L88 & ZR1, but they were open all the time - yeee haaa!

.

 

[WARVET]

Yeah, my 75 had the same as on the 73. WOT doesn't do much for anyone execpt marketing purposes. I have the original setup for my air cleaner, and the rubber that seals to the hood. I took the door off the assembly, and this allows clean air into the air cleaner all the time. I know it isn't giving me any extra HP, and it breaths better for sure. I do hear the QJet sucking air now.

 

[CAPNZ]

Thanks Mac!
Can I test this without the car running? As I said, "it bench tested fine".
Also, should I be able to see this switch or do I have to search for it?
TIA
"Jeff"

 

[CAPNZ]

That's what I have, a 73. Does it open when you start the car?
After further inspection I seen a foam rubber seal that slipped down.
This is where the baffle frame rests. It looks like this could have happened at the factory becuse I see indentations on the ends but not in the center.
IMO this is why the clips broke and someone cut the wires. It fell into the baffle.

"JEFF"

 

[CAPNZ]

UPDATE! on 73
OK, I got the wires soldered back together w/ heat shink tubing and put back in place.
I hung the unit from wires so I could see what happens from inside the cockpit.
I started the car, NOTHING.
I put it in drive and NOTHING.
HMMMM?
So I shut er down. I turned the key to the START position and pushed the pedal to the floor.
BINGO!!!
It woked perfect. Closed when I released the pedal.
So it works at WOT via a switch.
THANKS FOR ALL YOUR HELP!

CAPTAINZ

 

[srs244]

UPDATE! on 73
OK, I got the wires soldered back together w/ heat shink tubing and put back in place.
I hung the unit from wires so I could see what happens from inside the cockpit.
I started the car, NOTHING.
I put it in drive and NOTHING.
HMMMM?
So I shut er down. I turned the key to the START position and pushed the pedal to the floor.
BINGO!!!
It woked perfect. Closed when I released the pedal.
So it works at WOT via a switch.
THANKS FOR ALL YOUR HELP!

CAPTAINZ

congratulations! you just discovered the method used by every NCRS judge to check the full functionality of cowl induction hoods!!!

due to a limited amount of space, the corvette "cowl induction" hood only contains the inner flap control. for comparison, the cowl induction hood on my 71 454 el camino has 2 air intake "flaps", the one mounted on the top of the hood at the rear, which is operated off the carb vacuum and the inner flap (similar to the one on the vette) which is contolled by an accelerator switch/solenoid set up as described above. in concept it is much more efficient as the outer hood flap will open whenever you draw vacuum from the carb with the throttle. it doesn't have to be wide open. at wide open, both flaps open (the presumption is that you are now moving much more air over the hood, therefore you have more air to draw into the carb in a more direct manner. the concept is the bernoulli principle and is also the reason an airplane wing creates "lift" and a plane flys, lol)

steve

 

[JohnZ]

Meeting between Marketing and Engineering in 1972:

Marketing: "Hey, guys, we need something next year on the Corvette that makes a door open on the hood at WOT and makes lots of noise."

Engineering: "Why would you want to add that cost and complexity to the product when it doesn't increase performance or benefit the customer?"

Marketing: "Because it'll give the "illusion" of performance - a door opening and intake noise at WOT will sell like gangbusters."

Engineering: "OK, we've got old designs and hardware tooled from the '69 Camaro optional cowl hood, flapper valve and solenoid you guys also wanted back then; we can probably piggyback on that stuff and whip something up for you, but you guys have to pay for it."

Marketing: "COOL!! Let's do it!"

 

[kiwi vet]

Quote: Marketing: "Because it'll give the "illusion" of performance - a door opening and intake noise at WOT will sell like gangbusters."

Love it!!!

Sort of the like the Mr Mitchells "Lets design a car that LOOKS like it was designed in a wind tunnel"
The result a sexy looking car with the aerodynamics of a Brooklynn bus!

 

[69vettester]

Meeting between Marketing and Engineering in 1972:

Marketing: "Hey, guys, we need something next year on the Corvette that makes a door open on the hood at WOT and makes lots of noise."

Engineering: "Why would you want to add that cost and complexity to the product when it doesn't increase performance or benefit the customer?"

Marketing: "Because it'll give the "illusion" of performance - a door opening and intake noise at WOT will sell like gangbusters."

Engineering: "OK, we've got old designs and hardware tooled from the '69 Camaro optional cowl hood, flapper valve and solenoid you guys also wanted back then; we can probably piggyback on that stuff and whip something up for you, but you guys have to pay for it."

Marketing: "COOL!! Let's do it!"

----------------------------------------

 

[Vettehead Mikey]

So it works at WOT via a switch.

Gee imagine that, just like Mac said in the first response to this question........:L