Cowl Induction on '74 Vette
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Joined: Sep 2011
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From: San Juan Capistrano CA
Cowl Induction on '74 Vette
Hi, I have a '74 L82 that has the cowl induction - I'm not sure if they all had it or not. I don't think mine is working - but how would I know? Is there a way to test it? I see a brown and black wire going to the hood. I had heard once that there was a vacuum actuator somewhere. Thanks.
Drifting
Joined: Mar 2011
Posts: 1,886
Likes: 9
There is an electrical switch on the gas pedal linkage. When your foot is nearly to the floor, the switch closes and actuates the solonoid that opens the cowl induction air flap.
To test it, turn the ignition key to "run". DON'T START THE ENGINE YET. Fully depress the gas pedal.
You should hear the solonoid operate.
If you have to do a bunch of troubleshooting, disconnect the throttle cable from the carb, or you will flood the engine.
Also, you will notice that while driving at WOT, the induction noise will increase considerably. With stock mufflers, the induction noise can often be louder than the exhaust.
To test it, turn the ignition key to "run". DON'T START THE ENGINE YET. Fully depress the gas pedal.
You should hear the solonoid operate.
If you have to do a bunch of troubleshooting, disconnect the throttle cable from the carb, or you will flood the engine.
Also, you will notice that while driving at WOT, the induction noise will increase considerably. With stock mufflers, the induction noise can often be louder than the exhaust.
Thread Starter
Advanced
Joined: Sep 2011
Posts: 84
Likes: 0
From: San Juan Capistrano CA
Thanks, that seems like a straight forward test. Does the actuator require vacuum - and if so, I assume it gets the vacuum (when engine is off) from the vacuum canister? As for noise, the engine compartment is very quiet while driving so it makes me think its closed currently. I've never WOT it yet, so maybe mine works. I'll test it this weekend.
There is an electrical switch on the gas pedal linkage. When your foot is nearly to the floor, the switch closes and actuates the solonoid that opens the cowl induction air flap.
To test it, turn the ignition key to "run". DON'T START THE ENGINE YET. Fully depress the gas pedal.
You should hear the solonoid operate.
If you have to do a bunch of troubleshooting, disconnect the throttle cable from the carb, or you will flood the engine.
Also, you will notice that while driving at WOT, the induction noise will increase considerably. With stock mufflers, the induction noise can often be louder than the exhaust.
To test it, turn the ignition key to "run". DON'T START THE ENGINE YET. Fully depress the gas pedal.
You should hear the solonoid operate.
If you have to do a bunch of troubleshooting, disconnect the throttle cable from the carb, or you will flood the engine.
Also, you will notice that while driving at WOT, the induction noise will increase considerably. With stock mufflers, the induction noise can often be louder than the exhaust.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
There is an electrical switch on the gas pedal linkage. When your foot is nearly to the floor, the switch closes and actuates the solonoid that opens the cowl induction air flap.
To test it, turn the ignition key to "run". DON'T START THE ENGINE YET. Fully depress the gas pedal.
You should hear the solonoid operate.
If you have to do a bunch of troubleshooting, disconnect the throttle cable from the carb, or you will flood the engine.
Also, you will notice that while driving at WOT, the induction noise will increase considerably. With stock mufflers, the induction noise can often be louder than the exhaust.
To test it, turn the ignition key to "run". DON'T START THE ENGINE YET. Fully depress the gas pedal.
You should hear the solonoid operate.
If you have to do a bunch of troubleshooting, disconnect the throttle cable from the carb, or you will flood the engine.
Also, you will notice that while driving at WOT, the induction noise will increase considerably. With stock mufflers, the induction noise can often be louder than the exhaust.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Drifting
Joined: Jul 2002
Posts: 1,944
Likes: 20
From: The only Corvettes in Highett Victoria
Mike's right.
The only purpose it serves is to "intimidate" the person you're lining up against. At the drag strip, of course. And provided they can hear it above the exhaust of both cars revving up.
Regards from Down Under.
aussiejohn
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Melting Slicks
Joined: Jun 2003
Posts: 2,802
Likes: 241
From: Niles, MI
Zora Duntov,"compared to a non-ducted hood, it (the new for '73 ducted hood) cuts 0-60 mph times by a full second in the standard engine Corvette."
Mike Ward. "'all show' and 'no go'"
Who you going to believe?
Mike Ward. "'all show' and 'no go'"
Who you going to believe?
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Most would disagree that a cowl induction system is "all show and no go".
Every 11 degree reduction in induction air temperature will equate to a 1% HP increase. Underhood temps get pretty warm, especially in a Vette.
Also, some Chevy engineers named Roe, Piggins, and Shinoda designed the cowl hood induction system, first designed for SCCA and Nascar racing. Would GM put three of their top engineers to work on an "all show and no go" project?
More here:
http://www.camaro-untoldsecrets.com/...es/rpo_zl2.htm
and here,..
http://books.google.com/books?id=1sS...20test&f=false
Lastly, if you own a 73-75 Vette with a working cowl induction system, cut 5-6 pieces of yarn or string in 6" lengths and tape them to the back of the hood. Then take her for a "spirited" drive. You'll quickly be convinced the system works as the string is forced toward the engine's induction system.
FWIW
Every 11 degree reduction in induction air temperature will equate to a 1% HP increase. Underhood temps get pretty warm, especially in a Vette.
Also, some Chevy engineers named Roe, Piggins, and Shinoda designed the cowl hood induction system, first designed for SCCA and Nascar racing. Would GM put three of their top engineers to work on an "all show and no go" project?
More here:
http://www.camaro-untoldsecrets.com/...es/rpo_zl2.htm
and here,..
http://books.google.com/books?id=1sS...20test&f=false
Lastly, if you own a 73-75 Vette with a working cowl induction system, cut 5-6 pieces of yarn or string in 6" lengths and tape them to the back of the hood. Then take her for a "spirited" drive. You'll quickly be convinced the system works as the string is forced toward the engine's induction system.
FWIW
Drifting
Joined: Jan 2006
Posts: 1,832
Likes: 38
From: Cedar,BC
Yep, a world of difference on my 165 horse L48, once I got that flap optimized and tuned right, it sure did terrorize that hockey mom and her lil'ones quivering in their 1984 minivan last week...then again maybe it was the howl of the studded retreads...
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
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'.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
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'.
The most hilarious aspect of the "I make more power - I did the math!" brigade is that most of them a) make < 1.2 HP/CID, b) have likely never seen the far side of 80 MPH, no less 10/10ths on a road course or dragstrip and c) never bother validating their claims (because why should they?) on a chassis dyno or on the track.
Racing <> street.
I'm waiting for Mr. Two Inch Tube to weigh in here...
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
