Cowl Induction on '74 Vette
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
The big 'fail' with the stock system is that there's two large intake snorkels that are left wide open at all times. These are unfortunately positioned to suck in all sorts of hot air from the engine compartment.
As tested several years ago on my own car, actual temperature drop inside the air cleaner housing at 100 mph is a whopping 1-2*F depending on wind direction.
Burning Brakes
Joined: Jun 2010
Posts: 1,165
Likes: 93
From: Bellmore NY
I'd rather let the hot air out of the cowl, than let the induction mechanism dictate when cold air is "allowed in".
Last edited by Big Block Dave; Feb 20, 2014 at 02:08 PM. Reason: than vs then
Melting Slicks
Joined: Jun 2003
Posts: 2,802
Likes: 241
From: Niles, MI
It amazes me how gullible the peanut gallery is. Somebody with a desk dyno please calculate how much HP it takes to reduce a car's ET by 1 second in the 1/4 mile.
Now, given the rule of thumb that it takes a decrease of 11*F intake air temp to increase engine HP by 1%, figure out how much the intake temp would have to decrease to achieve this HP gain.
Finally- cowl induction systems don't really do much below 100 mph. They do nothing at a stand still, like at the start of a 1/4 mile. Any gains would come just as the car is approaching the 1320 mark, not much before.
A quick calc indicates that intake temps would have to be below absolute zero to achieve the supposed 1 second decrease in ET.
But the argument will go on 'cause Duntov told the press'.
Now, given the rule of thumb that it takes a decrease of 11*F intake air temp to increase engine HP by 1%, figure out how much the intake temp would have to decrease to achieve this HP gain.
Finally- cowl induction systems don't really do much below 100 mph. They do nothing at a stand still, like at the start of a 1/4 mile. Any gains would come just as the car is approaching the 1320 mark, not much before.
A quick calc indicates that intake temps would have to be below absolute zero to achieve the supposed 1 second decrease in ET.
But the argument will go on 'cause Duntov told the press'.
But now that you're on a roll, would you care to weigh in on the function of the C-clips on the stub axles? :-)
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I saw a comment about replacing c-clips and side yokes the other day 'for safety'.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
I did the same thing, except mine might be in the attic. Im sure it does "something", but realistically I think it largely acts as a sound deadener for engine noise, except for full throttle conditions. With it removed, there certainly is alot more engine "sound" into the cockpit.
I'd rather let the hot air out of the cowl, than let the induction mechanism dictate when cold air is "allowed in".
I'd rather let the hot air out of the cowl, than let the induction mechanism dictate when cold air is "allowed in".
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Yeah,..all those stupid cowl hoods I saw at the drags last weekend,..some 6" tall, I'm sure are just "for show". And fresh, cool air to the carburetor,..what a stupid idea!
Last edited by 73, Dark Blue 454; Feb 20, 2014 at 05:10 PM.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
I'll eat humble pie on this one. My thought was that heat would flow from the front of the engine back and out through the cowl vent (with induction unit removed). But even with the unit removed the passage to the cowl vent is still sealed off by the rubber ring on the air cleaner to hood interface. So while air can be sucked into the carb - and I can certainly hear it - venting in the other direction is not really possible with the rear hood seal blocking off the cowl vent. So I fouled up. My apology to you and other readers! Heck, I just drive my car. I don't have ribbons on it.
Excuse? Well not really. Been doing my income tax today...paid out a 1974 convertible equivalent last year. Love these taxes in Canada.
Excuse? Well not really. Been doing my income tax today...paid out a 1974 convertible equivalent last year. Love these taxes in Canada.
Last edited by Paul L; Feb 20, 2014 at 07:26 PM.
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Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I'll eat humble pie on this one. My thought was that heat would flow from the front of the engine back and out through the cowl vent (with induction unit removed). But even with the unit removed the passage to the cowl vent is still sealed off by the rubber ring on the air cleaner to hood interface. So while air can be sucked into the carb - and I can certainly hear it - venting in the other direction is not really possible with the rear hood seal blocking off the cowl vent. So I fouled up. My apology to you and other readers!
Hmmmmmm.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
I'm not saying or thinking that the concept is wrong. There's no real reason why air from the engine compartment couldn't enter the air filter housing through the snorkels and flow backwards through the cowl induction duct into the windshield plenum if the flapper is removed.
Hmmmmmm.
Hmmmmmm.
a second is idiotic.
Burning Brakes
Joined: Jun 2010
Posts: 1,165
Likes: 93
From: Bellmore NY
I'll eat humble pie on this one. My thought was that heat would flow from the front of the engine back and out through the cowl vent (with induction unit removed). But even with the unit removed the passage to the cowl vent is still sealed off by the rubber ring on the air cleaner to hood interface. So while air can be sucked into the carb - and I can certainly hear it - venting in the other direction is not really possible with the rear hood seal blocking off the cowl vent. So I fouled up. My apology to you and other readers! Heck, I just drive my car. I don't have ribbons on it.
Excuse? Well not really. Been doing my income tax today...paid out a 1974 convertible equivalent last year. Love these taxes in Canada.
Excuse? Well not really. Been doing my income tax today...paid out a 1974 convertible equivalent last year. Love these taxes in Canada.
Edit: I looked back at your picture of the actual flapper assembly. It seems that you replaced the plastic support under the hood...I believe I left that piece off.
Last edited by Big Block Dave; Feb 22, 2014 at 07:16 AM.