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Difference between stock and cowl hood?
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DRR Pro
Picture of Footloose
posted
What difference in ET between the both. With cowl not sealed? I forgot. This is using a Nova.
 
Posts: 1921 | Location: in a van down buy the river | Registered: September 07, 2002Reply With QuoteReport This Post
DRR S/Pro
Picture of Lenny5160
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I wouldn't expect any. When I made the change, a different engine went in so I can't say for certain. I don't think the small difference in airflow would do anything and I went steel to steel, so there were no weight savings.


Tony Leonard
 
Posts: 3148 | Location: Inver Grove Heights, MN | Registered: March 18, 2004Reply With QuoteReport This Post
DRR Sportsman
Picture of FootbrakeJim
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With the cowl not sealed, I don't know if it will, help, hurt, or run the same. When I added a cowl scoop to my hood, I first cut a 16x18" opening in the hood beneath the cowl. Ran it that way, and saw virtually zero difference in ET or MPH vs. previous runs in nearly identical conditions. Figured it was still breathing hot underhood air. I guess it is mostly about pressure differential - depending on the car, mine may have been blowing hot air out of that cowl, rather than bringing in cooler outside air. I later bought a 2'x3' sheet of .100" thick aluminum, cut a 12 inch hole in it, and pop-riveted it to the base of my air cleaner, then glued on a 4" tall wall of 2" thick, gray, closed-cell foam around the perimeter, to seal it to the hood. That ensures it breathes only outside air, and made an immediate difference in both ET and predictability, (not necessarily consistency), because it was no longer breathing super-heated air off the headers, and/or through the radiator. But no way you can nail down to a specific ET gain, because that varies, with the difference in air temperatures between engine compartment vs. ambient (outside) air. The cooler the outside weather, the bigger difference in ET.

Here is a trick I read about in one of the old Alex Walordy E.T. drag racing books from about 30 years ago: Tape several 2-3 inch long strands of yarn or string along the edges of your cowl or scoop, and take video of them as you are going down track, they should be blowing into the scoop. If not, you have a pressure differential problem.
And here is my explanation on the "consistency" vs "predictability" of it: The car was definitely quicker afterward, (I'd have to dig up old logs from 15 years ago, but IIRC it was a difference of around .01-.03), but it may have been a bit more consistent without the air pan, because I always ran the car with a specific amount of heat in the engine, and so it was always breathing heated air, no matter the outside temp. BUT, when I began using a weather station, the prediction feature was almost worthless, until I sealed the air inlet to the cowl. Suddenly the ET predictions were a LOT closer, and I realized then, that the engine was now taking in the same "quality" of air that the weather station was sampling. That unit was calculating it's ET prediction on the ambient air temp, not the 200*-600* stuff my engine had been breathing before...

This message has been edited. Last edited by: FootbrakeJim,


Dan "Jim" Moore
Much too young to feel this damn old!!
 
Posts: 1032 | Location: Farmersville, TX  | Registered: December 05, 2002Reply With QuoteReport This Post
DRR S/Pro
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I've never understood why a guy would run a cowl, in a racing scenario, when there aren't any rules prohibiting a front facing scoop. But I know a lot do for what ever reason.


Illegitimi non carborundum
 
Posts: 2330 | Location: OKC, OK | Registered: February 15, 2008Reply With QuoteReport This Post
DRR Sportsman
Picture of SonnyJames
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^^^^^ that said why would anyone bracket racing run any air scoop??...other than needing space
 
Posts: 680 | Location: Consistently researching inconsistencies | Registered: September 04, 2001Reply With QuoteReport This Post
DRR S/Pro
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None, blocked off factory cowl on my stocker and the car picked up. Just looks better.

^^On a 69 Camaro Stocker anyway..

This message has been edited. Last edited by: BP758,


Raceless in California!
 
Posts: 4470 | Location: Vacaville  | Registered: January 07, 2004Reply With QuoteReport This Post
DRR Sportsman
Picture of McK_Racing
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I have a 4" cowl hood on my Camaro, and I think the cowl hood looks better than a flat hood. I haven't tried running with it sealed just because I haven't taken the time to build a pan, so I can't compare with and without. It's a street driven car too, so I don't want something facing forward.

Driving down the road when there's water on the hood from dew or rain, you can watch the drops as they come off the back of the cowl get sucked into the scoop opening, so there's definitely airflow into it. Also, to run the air cleaner, restrictor plate spacer, and manifold combination that I use, I need the taller hood clearance. I have barely 1/4" between the air cleaner wing nut and the center crease in the hood. I even try to turn the wingnut so it aligns with the crease.

This message has been edited. Last edited by: McK_Racing,
 
Posts: 250 | Location: Northern Hemisphere | Registered: February 23, 2008Reply With QuoteReport This Post



DRR S/Pro
Picture of Lenny5160
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quote:
Originally posted by SonnyJames:
^^^^^ that said why would anyone bracket racing run any air scoop??...other than needing space


In my case, the car looks like a Stocker but the throttle stop won't fit under the stock hood. I think a big scoop would look odd on it.


Tony Leonard
 
Posts: 3148 | Location: Inver Grove Heights, MN | Registered: March 18, 2004Reply With QuoteReport This Post
DRR S/Pro
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Tony, I tried the KN sealed to the hood, open at cowl. Car was never consitent. At a divisional race I duct tapped it up. Car picked up so I put a flat top on the air cleaner and it’s still that way. Removed duct tape and closed factory flaps and sealed it.


Raceless in California!
 
Posts: 4470 | Location: Vacaville  | Registered: January 07, 2004Reply With QuoteReport This Post
DRR S/Pro
Picture of Lenny5160
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quote:
Originally posted by stk 758 BP!:
Tony, I tried the KN sealed to the hood, open at cowl. Car was never consitent. At a divisional race I duct tapped it up. Car picked up so I put a flat top on the air cleaner and it’s still that way. Removed duct tape and closed factory flaps and sealed it.


This car was good when the milled choke horns were almost touching the stock hood, and I didn't notice any change with the cowl hood. I've never made any attempt to seal the carb or direct air flow. I've also never run an air cleaner on this car.


Tony Leonard
 
Posts: 3148 | Location: Inver Grove Heights, MN | Registered: March 18, 2004Reply With QuoteReport This Post
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I’m running a Quickfuel ( Zach Baker) 780 with the choke flap in. Mines close with a big drop base.


Raceless in California!
 
Posts: 4470 | Location: Vacaville  | Registered: January 07, 2004Reply With QuoteReport This Post
DRR Pro
Picture of Footloose
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There are a lot of good credible experiments here. My cowl hood is steel. I liked the way it looked when I was younger, not so much any more. I still have the factory hood. I wondered while going down the track,what about all the air coming through the grill. Will it catch all the air to the firewall. Maybe slow it down. I had to have a tall hood because I ran a blower for years.
 
Posts: 1921 | Location: in a van down buy the river | Registered: September 07, 2002Reply With QuoteReport This Post
DRR Sportsman
Picture of FootbrakeJim
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quote:
Originally posted by Footloose:
There are a lot of good credible experiments here. My cowl hood is steel. I liked the way it looked when I was younger, not so much any more. I still have the factory hood. I wondered while going down the track,what about all the air coming through the grill. Will it catch all the air to the firewall. Maybe slow it down. I had to have a tall hood because I ran a blower for years.

Yes, exactly why it is worth experimenting, every car is different. I do think a lot of factors play into it. Such as: Have inner wheel tubs been removed, (allowing for exit of excess air coming through grille/rad), are headers wrapped, does car have a thermostat, is car run with cool or hot engine, actual body design of car/aerodynamics, what fuel is being used, etc.
I do know my car was more consistent, but a hair slower, without the "cold/fresh" air induction, but is far more predictable with it.
My cowl is a 4", I do think it looks a lot better than a flat hood. Some 6" cowls are too much for my liking, depends on the car.
Another thing, is the Harwood cowl hood I bought for my son's Chevelle, did not allow for much air flow. Small openings with screens on them. Mine is fully open on the back.
Another variable, is placement/location of the rear edge of the cowl. When GM designed the cowl hood, it was a great piece of engineering. Their wind tunnel testing found there was a high-pressure area at the base of the windshield. So the rear-facing cowl yielded the same pressurized induction benefits as a forward facing scoop like the Mopars had, but without the additional drag, or sucking in a ton of water. But if that cowl is not positioned correctly, you can create a low-pressure situation, which will hurt performance. The factory cowls didn't really benefit performance a lot, because they were only 2" tall, and didn't flow a lot of air volume.


Dan "Jim" Moore
Much too young to feel this damn old!!
 
Posts: 1032 | Location: Farmersville, TX  | Registered: December 05, 2002Reply With QuoteReport This Post
DRR Pro
Picture of HS professor
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25 yrs ago I had a 69 Camaro that I built as a real looking Yenko clone. Had a 454 though that ran 12.0's with McCreary street tires. Ran the car for a year straight always going low to high 12.0's weather dependent, NEVER in the 11's. Finally pulled the plug on a factory Cowl induction air cleaner with the rubber ring to seal to the hood and the car never ran 12.0's again, always 11.90's. I did A-B tests and the air cleaner on that car was worth .05 - .08 every time I tested it. I remember you could hear the air being sucked in at the back of the cowl at idle .
 
Posts: 1421 | Location: Monroe twp nj | Registered: December 05, 2005Reply With QuoteReport This Post



DRR Sportsman
Picture of Steve from Pa
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Slow 11.90 foxbody mustang here with cowl hood on alchol.
I tried several different things:
A pan sealed to the carb
Just a air pan not sealed
No air pan
All with and without a KN stub stack.

ya know what works the best for consistency - nothing at all on top of our carb, and the cowl hood opening sealed closed! I don't understand why, but is is better with out a doubt with no fresh air.


Most important, keep the shiny side up
 
Posts: 798 | Location: Punxsutawney, Pa USA | Registered: February 05, 2001Reply With QuoteReport This Post
DRR Trophy
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I think each car is different on my Malibu a sealed cowl scoop made it repeat much better.
 
Posts: 39 | Location: ohio | Registered: August 15, 2009Reply With QuoteReport This Post
DRR Top Comp
Picture of wideopen231
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On subject of forward facing scoop and rear facing cowl. Probably zero difference. Based on fact I watched a guy turn enderle hat around backwards to prove air down track made no difference. He ran exactly the same with hat facing backwards as he had with it correctly facing forward.




America home of free. Brought to you by 2nd amendment.
 
Posts: 4169 | Location: Greensboro NC | Registered: May 24, 2011Reply With QuoteReport This Post
DRR Sportsman
Picture of botmbulb
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quote:
Originally posted by wideopen231:
On subject of forward facing scoop and rear facing cowl. Probably zero difference. Based on fact I watched a guy turn enderle hat around backwards to prove air down track made no difference. He ran exactly the same with hat facing backwards as he had with it correctly facing forward.


Injected on alcohol, I can see that. On gas, that's a whole different story.
 
Posts: 490 | Location: Hammonton, N.J. | Registered: March 06, 2001Reply With QuoteReport This Post
DRR Pro
Picture of Mike Beck
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Cowl hood sealed to the top of my throttle body, would never NOT do this on a car. My slower car is setup the same way. A good friend of mine drove my car this past weekend and almost made a Xerox pair of timeslips like the picture below. I drop a little over 22* air temp on a 1/4 mile pass.

 
Posts: 1444 | Location: South River, NJ | Registered: June 19, 2007Reply With QuoteReport This Post
DRR Trophy
Picture of Bad Nusz
posted Hide Post
quote:
Originally posted by FootbrakeJim:
With the cowl not sealed, I don't know if it will, help, hurt, or run the same. When I added a cowl scoop to my hood, I first cut a 16x18" opening in the hood beneath the cowl. Ran it that way, and saw virtually zero difference in ET or MPH vs. previous runs in nearly identical conditions. Figured it was still breathing hot underhood air. I guess it is mostly about pressure differential - depending on the car, mine may have been blowing hot air out of that cowl, rather than bringing in cooler outside air. I later bought a 2'x3' sheet of .100" thick aluminum, cut a 12 inch hole in it, and pop-riveted it to the base of my air cleaner, then glued on a 4" tall wall of 2" thick, gray, closed-cell foam around the perimeter, to seal it to the hood. That ensures it breathes only outside air, and made an immediate difference in both ET and predictability, (not necessarily consistency), because it was no longer breathing super-heated air off the headers, and/or through the radiator. But no way you can nail down to a specific ET gain, because that varies, with the difference in air temperatures between engine compartment vs. ambient (outside) air. The cooler the outside weather, the bigger difference in ET.

Here is a trick I read about in one of the old Alex Walordy E.T. drag racing books from about 30 years ago: Tape several 2-3 inch long strands of yarn or string along the edges of your cowl or scoop, and take video of them as you are going down track, they should be blowing into the scoop. If not, you have a pressure differential problem.
And here is my explanation on the "consistency" vs "predictability" of it: The car was definitely quicker afterward, (I'd have to dig up old logs from 15 years ago, but IIRC it was a difference of around .01-.03), but it may have been a bit more consistent without the air pan, because I always ran the car with a specific amount of heat in the engine, and so it was always breathing heated air, no matter the outside temp. BUT, when I began using a weather station, the prediction feature was almost worthless, until I sealed the air inlet to the cowl. Suddenly the ET predictions were a LOT closer, and I realized then, that the engine was now taking in the same "quality" of air that the weather station was sampling. That unit was calculating it's ET prediction on the ambient air temp, not the 200*-600* stuff my engine had been breathing before...


Thanks, Jim; one of the best posts I've seen on any forum. I use a weather station myself and have puzzled some over why sometimes the air can change, but my ET's don't. I draw air from under the hood on my S10. I've thought about putting a temperature sensor right inside the air cleaner.
Cheers! Troy
Troy
 
Posts: 327 | Location: Sioux Falls, SD | Registered: March 17, 2018Reply With QuoteReport This Post
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