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What is Cowl Induction?

26K views 31 replies 20 participants last post by  Fred Ficarra 
#1 ·
I was reading that I can add HP by adding Cowl Induction to my car. But how does Cowl Induction work, and what do I need to do?
 
#2 ·
Cowl induction is when the back of the hood next to the windshield is open so that the engine can get access to the cool high pressure air that builds up there while driving.

Stock cowl induction hoods were options on first gen cars. They are the ones w/ the "low wide" hood scoop facing rearward down the middle of them. Real ones had matching air breathers that fit up tight under them to take advantage of the cool air. And, yes your car will make slightly more power w/ the cooler air the engine can suck in using a cowl hood thats open. Hope this helps. pdq67
 
#3 ·
A cheaper option would be to fabricate a cold air induction sytem. There was an article in Super Chevy magazine a while ago about this. Get an old air cleaner base and lid, two aluminum gutter downspouts, some flexible ducting, some thin sheet metal, and some rivets. Attach the two downspouts to the inside edge of the front of the air cleaner base with the rivets and then wrap the sheet metal around the remaining area of the cleaner base and attach with rivets. When you put the cleaner lid on, the edges of the sheet metal and downspouts should be inside the lid. Then run the flexible ducting down from the downspouts to your front bumper area where there are holes allowing fresh air in. This should force the air cleaner to take in only fresh, cold air from the outside.

Garrett M.
68 Camaro
 
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#17 ·
The tiny amount any additional pressure has next to zero effect on power..

Cowl induction is purely about the induction of cold air, and the cowl's slightly higher than ambient air pressure is simply the best place to induct it. :)

Open your kick panels vents.. That's how much pressure there is at the cowl. Hardly enough to consider it as "boost".
 
#10 ·
yeah, but $600 saved up in the 9 years since this thread was started comes down to $66.66 a year, or $5.55 a month, which certainly seems doable...
 
#12 ·
I think it's the "cool" factor that is raised about 100 shp, (smiles per Horsepower) because those hoods look so darn cool !
 
#19 ·
45Hp.. l:)

Most of those cars at the race track have cowl hoods simply for cosmetic reasons with few being functional. When the hood is left open at the rear the hood acts as an extractor that can also have its own benifits at higher speeds.

So the cowl hood can serve two entirely different purposes depending on how its set up. I would say also depending on the earodynamics and rake of the windshield "make/model" its not always the best source to tap into for an intake but its always a good source to use to extract.
 
#20 ·
Very few if any are "functional" at the track. When I say functional I am refering to how the factory designed it. That doesn't mean that that's the only purpose,these days most cowl type hoods are used for extra clearance and looks.
 
#21 ·
OK Steve, guess they don't have an info source like Hotrod Magazine down in Australia.
We do in NZ, but the colonies like Aussie, maybe not lol

Open your kick panels vents.. That's how much pressure there is at the cowl. Hardly enough to consider it as "boost".
Well even the slightest pressure, even if only measured in HG water...(not mercury) over comes any need for the carb to 'drag' air in, AND over come pressure drop (HG water column) thru the air filter....
THEN add the diffrence between cold air and engine bay air thats cooled the radiator...

On there own each makes a difference....combined a significant diference.... enough difference for more modern car manufactors spend huge money on R&D, and impliment very similar systems in a market that is very competive.
 
#22 ·
We do in NZ, but the colonies like Aussie, maybe not lol


Well even the slightest pressure, even if only measured in HG water...(not mercury) over comes any need for the carb to 'drag' air in, AND over come pressure drop (HG water column) thru the air filter....
THEN add the diffrence between cold air and engine bay air thats cooled the radiator...

On there own each makes a difference....combined a significant diference.... enough difference for more modern car manufactors spend huge money on R&D, and impliment very similar systems in a market that is very competive.
:thumbsup:
Have you ever seen a late model performance car without engine air directed to it from outside the engine bay? That's why turbo's are inter-cooled. Well, that and overcoming compression heat.
 
#24 ·
Thank you Aaron!!! You're very kind.

Love that shot, but,,,,,,,,,, ya know, another one is kinda moving close to the top.;)
 

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#26 ·
Donahue thought enough of it to make the 69 Blue Maxi Camaro hood full time operational and claims they saw small hp gains from doing this. Not sure what they did to make it full time functional, but I assume they removed the door from inside the rear of the ducted hood. That's the way 99% of them are run today because as already pointed out most guys run them simply for cosmetic or hood clearance purposes and aren't into correctness. Actually of those 99% most of them don't have the cowl air cleaner sealed to the hood and if they do it probably still has an opening into the engine compartment, so they probably see no difference using this hood.

I don't think it has anything to do with increased pressure. I think it has everything to do with reduced ambient air temperatures ducted directly into the carb and not allowing any underhood higher temps to affect the air temperature. If that's the case the plenum air cleaner did a much better job of this as it has no snout on it to allow any underhood air into the carb.

I am a fan of the ZL2 hood, but I think the functional Chevelle cowl induction hood is nicer with the vacuum actuated outer door and the electric actuated inner door. I always loved watching the outer door open when you got into the pedal.
 
#27 ·
I am a fan of the ZL2 hood, but I think the functional Chevelle cowl induction hood is nicer with the vacuum actuated outer door and the electric actuated inner door. I always loved watching the outer door open when you got into the pedal.
Huge fan too, and also thought it would be nicer with a vac opening mechanism..
Perhaps with the late arrival of RPO ZL2 in Dec68-Jan69, the vacuum actuated door may have been too complex for it's rushed(?) development or required modification of existing components already being fitted to these cars.
The components made to operate and retrofit a ZL2 are very simple. A different accelerator arm with a switch, firewall mounted relay, a hole & grommet for the loom, and simply plug it in to the fusebox.
 
#29 ·
Air pressure; At highway speed, open your Astro vents and note the air volume and force. While drag racing keep them closed. The wall of air against the windshield will thank you for it.
As for that snorkel, there are ways to help it.:yes:
 
#30 ·
Fred, I never get tired of looking at your car, it's absolutely beautiful
I have to agree...sort of....back side engine bay yep
BUT I have never liked the hidaway head light grill. lol

Im sure it was an old US hot rod mag from the 70s I have here (have boxes and boxes of them) there was an articule about using a box full of ice to cool air...and sort of recollect comments about the extra weight over the benefts...can rem which way that went.

Have you ever seen a
late model performance car
without engine air directed to it from outside the engine bay? That's why turbo's are inter-cooled. Well, that and overcoming compression heat
performance? hell they damn near all, including little shopping baskets do it now.
 
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