So, just so I am on the same page with everyone else from the start: Cowl induction is: and the ram air style: I can understand how the air is getting forced into the front in the ram air style, but how does a cowl hood work? I assume it is based on air pressure or something. Which do you think is better and why? ------------------ 1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in... -=ICON Motorsports=- [This message has been edited by Biochem (edited March 16, 2001).]

Cowls get thier pressure from the base of the windshield. If you ever see an air tunnel photo there is a high pressure area all along the base of it.
I think the ram air hoods are ugly, but thats just MHO.

------------------
"American made baby. 100% American iron. The muscle among the masses. My hero. Yep, you can take your ergonomically designed, space age, computer controlled, 4 door, cup holding map lighted split double wishbone split fold down retractable cargo covered moon roof piece of transportation and keep it. For I have felt the thunder. And I know the difference!"
JSP Motorsports
ICON Motorsports

one vote for the cowl.

I call the cowl hood the convertible affect. If you sit in the a convertible (best is a tracker with the windows rolled up) the air blows at the back of your head. I could explain this scientifically but I currently lack the motivation.

However, the force you'd notice from going foward is less than the wind blowing back at you. The ram-air would ram more air, however, it would be an almost negligible amount when compared to true forced induction.

------------------
1984 WS6 Hardtop Trans Am
Former L69 Car under restoration
1984 T-top Trans Am
4-bolt main 350, performer intake, headers, Holley 650, T-5, hayes clutch, dual elec. fans and 3.23's.
Daily driver and restoration
13.98 @ 101

So it is more or less a turbulence thing? Or is it high pressure that instead of running up the windshield, it goes back under the cowl?

What is better with all things being equal? I would assume the Ram Air does move more air, especially at lower mphs, but is it enough to really matter?

I wonder if the Ram Air also would cause problems with the way the cooling system is set up. Isn't there supposed to be a low pressure area behind the radiator caused by the air dam under the front? Wouldn't air comming in from above disrupt that? I guess if you have an air box, it doesn't matter too much...

I think it's more matter of personal preference. Either will get the job done. The cowl hood works becuase air basically "piles up" in front of the windshield and at it's base it has nowhere to go so pressure builds slightly and the back of the cowl induction hood opens into this area giving the air a place to go- into the carb. The ram air style hood does the same thing but it uses two opening of it's own facing forward to create the high pressure area. Don't worry about radiator cooling with either of these setups- the tiny amount of air that leaks past them won't affect the amount of air passing through the radiator at all.

Ram Air is better as far as making more power. The amount is not a lot, 15 HP give or take. The faster you go the more you get. The Ram Air is a poor mans supercharger. The cowl induction gets you cold air but not much ram effect.
I like Ram Air!

Another thing I am seriously wondering about with the Ram Air style is what about rain when you drive? I figure a cowl induction won't saturate the air filter as much... BTW, I plan on making it functional too, not just a hole with an open air cleaner under the hood, but actually some kind of pan and some foam around the sides or something. Brandon (KarpsTA) has some ideas with his ram air hood too... All ideas for that are welcome!

------------------
1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

If a Ram Air hood is properly designed then rain shouldn't be a problem. The designer will put two walls in the intake path to force the incoming air down then up with drain holes at the base of the second wall which comes up from the bottom. This forces most of the moisture out, but not all of it. I built a functional cowl induction once, it was easy go to a crafts store and get some foam rubber like they put into upholstery. They also sell some 3M glue made just for the stuff. That way you cut the foam to size and then glue the ends together. I used clear silicone to stick it to the pan. It worked well, make sure to put a couple of drain holes in the bottom of the air pan on the cowl induction unit as well, because you WILL get water into it! More than a Ram Air unit because the hood slopes toward the opening on a cowl induction unit and away from a Ram Air unit. And if anyone cares, the cold air induction units on the 3rd gen firebirds with the power bulge hoods is too far forward of the base of the windshield to benifit from the high pressure zone. In fact it has a slightly lower pressure as it tries to act more like an air extractor.

An important thing to remember for this discussion is that all the 4th gen 'ram air' hoods are a farce. There is no ram air going on.
Why? Simple, laminar flow effects. Even at high speeds, there is a boundary layer of air next to the surface that basically doens't move. In order to get true ram air you'r inlet has to be several inches about the hood.
Want proof? Look at Pro stock cars and their tall snorkels. Why would they run those if it wasn't the most effective way to get true ram air. Think of the aerodynamic nightmare that presents. If a 4th gen style ram air worked, don't you think they run a low profile scoop to save on wind resistance.
...ed

I have to disagree with Ed. He is right their is a boundary layer and laminar flow layers on the hood, but they aren't very thick. You do and will get a Ram Air effect from a 4th Gen type Ram Air hood as the opening is near the front of the hood and is several inches tall. Pro Stock Hood scoops are tall by necessity. They use sheet-metal intakes that stick up past the hood line, top that with a pair of Holley Dominators and you have a tall hood scoop to clear the top of the carbs and to get your fresh air. By placing a scoop higher you will get the scoop into clean air so it works better. A scoop close to the top of the hood is in the turbulent air flow zone. This means in order to double the flow you have to quadruple the pressure or the Ram Air Force. If it were a laminar flow it is fairly proportional twice the flow with twice the force.

Hey, this interests me, seeing as I have a (functional?) cowl of this type. If I fabricate a shroud to extend the cowl up to the windshield, will it be more effective? Please advise, thanks!

------------------
DR Stevens
Car #1: my ride
1984 TransAm
305HO(L69) 96K & counting
750 cfm Q-Jet/Holley rem.
K&N filter
700R4/Superior shift-kit
and trans cooler
3.42 rear/3.73 blew up!!
underdrive pulleys
Accel HEI Super-Coil
180 stat/hi flow water
pump/Jet fan switch
dual snorkel/'84 cowl
3" exhaust of some sort
partial emissions delete
Car #2: My wife's ride
1991 Firebird/Formula
305TBI(LO3) 99K & smoking
K&N air filter
Hypertech Chip
more engine mods later
"Hey, Uncle Sam!! Where's my f**king tax return??!!"

most cowls open up in about the right area already on the windshield side. White racing/sheet-metal fabricating makes carb/hood pans to mate up to cowl air induction hoods.
If it's more underhood cooling you want then just open up the area under the windshield wipers. I have removed the sheetmetal between the wipers and the engine compartment for cooling, and my ram-air feed comes from the nose (fog-light) area at the front of the car.

Eight4 TA - I wouldn't bother with it. The amount of gain would be negligible, so why butcher your hood for little or no gain. A true cowl induction hood like one from Harwood has the opening at the base of the windshield where it belongs.

Eight4 TA-- Don't mess with it unless your cowl solenoid goes bad like mine did (not made anymore) It serves a purpose, that could be done better, but the fact that you have a working one on the vehicle makes the car more valuable in that sense.
When the solenoid died on my cowl, i took the unit off and got an open element air cleaner. This let some hot air escape through the hood bulge, and cool the engine bay a bit. You can see the heat radiating out sometimes. The only disadvantage is that it has to be sealed when it rains.

------------------
--Steve S--
1984 Trans Am 305 LG4, 5 speed
Daily Driver, Flowmaster 80 Series
Holley 600 cfm & vacuum advance

Well, my solenoid & vac switch were both shot when I got the car-I took the door out of the airbox and jettisoned the bad solenoid so there's no moving parts now.

I won't bother trying to redesign the cowl if I won't gain anything like Flash says. Had my hopes up for awhile there! I do want to keep my hood though, i've got the original decal & stripe kit restored to the car.

DR

Ed and Damon are right; the layer of air that moves along with the car is at least 1½" thick at all places, so in order to get any actual "ramming" at all, the scoop has to have the bottom-most part of its opening at least that far above the body work.

Additionally, the windshield acts like a giant air dam, and has a huge high-pressure area at its base, where air that smacks into it and can't get out of the way just collects. This effect is far greater than anything you can get by "ramming" air into a forward-facing scoop until you reach a very high speed. The NASCAR guys use cowl induction because even at their speeds (150-200 MPH) it's more effective than even a duct to the nose of the car would be.

Any HP gains people claim to get from "Ram Air" are purely due to cold air induction.

The highest pressure point on the body of a car is the base of the windshield. You'll get more positive results by ducting to there, than anywhere else.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

In a perfect world, ram-air would not be affected by rain, but on my '71 Mustang (I guess that makes me bi-chevy/ford, forgive me), it runs like A$$ when it rains, or when it is extremely humid for that matter (even with a K&N Filter) {NO FORD CRACKS PLEASE, it's a great car!}. I prefer the look of ram-air, but not the functionability (is that a real word?). The other thing is that with ram-air on a daily driver, your engine comapartment will get extremely dirty, extremely fast, if that sort of thing is important to you. Just my 2 cents.

------------------
"If you ever drop your keys into a river of molten lava, let'em go, because, man, they're gone." - Jack Handey

85fc, your f*rd runs bad in the rain b/c the distributor is in the front of the block, thus it gets wet very easily. At least thats the more likely reason.
...ed

A 71 Mustangs Ram Air system doesn't have any redirecting dams to prevent the water from getting in. It also has flapper valves so the Ram Air is only functional at WOT otherwise it sucks air in through the snorkel on the air cleaner. Totally different from todays Ram Air systems. If your car runs bad even in high humidity then I'd start looking for an ignition problem. Nascar racers put the opening at the base of the windshield beacuse Nascar mandates it to help keep the cars looking stock, not because that is where they get the highest pressure. Also to dispute the 1 1/2 inch air layer theory, the worlds fastest stock bodied car is a 1991 Pontiac Trans Am. It has dual air feeds to the engine. Both forward facing and both barely above the top of the hood. If more air/power could be gained from placing the air intake at the base of the windshield I'm sure it would be there. Different cars have a different amount of a boundary layer and laminar layers next to the hood. It is dependent on the rake of the hood, the deflection of air by the nose of the car, the speed of the car/air, and the texture of the hood. All things being equal I doubt anyone will ever be able to tell any difference between a Ram Air hood and a Cowl Induction Hood on a street car. When I talked about 15 HP that was compared to a regular air intake. Compared to Cowl induction it's very little.

Flash, it's not just theory. NASCAR racers could just as easily run an ir duct to a headlight location or elsewhere in the grille, like they used to before they discovered that using the windshield cowl made the car go faster. You're right though, on a street car, very little of this makes any difference; as long as you feed the engine cold air, you've done about all you can do. The main reason for "Ram Air" packages is fr styling: people who don't know anything about fluid flow physics still think it looks cool and will pay extra to get it.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

Okay, so we pretty much agree. I still don't believe that you get more air at the base of the windshield than a good Ram Air setup, but I can't prove it with any hard numbers. I still prefer Ram Air!

true the factory ramair hoods function more as a cool air induction and are primarily for looks.
There is a large high pressure area at the base of the windshield, but there is also at the nose of an fbody as well. Neither area would function as a 'true' ram air entrance, but those induction systems still function based on the amount of pressure that builds up in those areas. In that respect, either area is functional.

When you blow an engine you put the supercharger between the intake manafold and the carb, not on top of the carb. how much extra pressure can you put on top of the carb by means of ram air or cowl induction? My compression ratio is 10:1 which doesn't leave a whole lot of room for supercharging, but if I could put a fan in my intake somewhere and boost it to 11.5 that would be cool. I don't want to put anything under the carb because I only clear my hood by about 1/2 inch and don't want to mess with that.

Just for clarification the old Shelby's could be had with a Paxton Supercharger and they put a container around the carb and blew through the carb instead of pulling through it.
As far as modding your car Pro-Stockers do 200 MPH and are pushing air into the carbs.

Thanks flashGTA, I didn't know that could be done. Anyway, here's a thought that's a little more on topic. Air flows from an area of greater pressure to an area of lesser pressure. I'd be willing to bet that if you built a hood with both ram air and cawl and connected the two you would have air going in the ram intakes and out the cawl. Front to back. That means you have more pressure from the ram air. Two more points of difference I see are that air coming in a cawl has already blown past a hot hood, and air that is taken into a ram intake is air that wont pile up against the windshield and cause drag. I don't know how significant these factors are but I thought I'd through them out to be considered by those who know more then I.

I was digging around and found an article in an old Hot Rod that touched on this subject. It was chronicling the build up of an 99 LS1 Camaro SS. They tried opening up the Ram Air hood more on it and got no improvement in performance. They felt in part due to the convoluted routing on these cars. They then cut some openings in the bottom of the airbox so it would draw in air from in front of the A/C condenser and that improved performance. So the Ram Air hood on an SS is actually a hindrance, rather than a help.

The scientific explanation for a cowl induction system is based on the principle that changing the direction of air flow increases its pressure. The windshield forces the air to change direction by about 40 degrees from horizontal. That increases the pressure at the base of the windshield and makes the air flow toward a lower pressure area, the engine compartment.

vote me for cowl induction...

underhood = lower pressure
near the windshield = higher pressure

the higher pressure air just moves into the area of lower pressure (?)

Try this on for size. Our cars already have a functional cowl induction system built in. ALL modern production cars have this same system.

Got your attention yet?!

Where do you think the air comes from that blows out of your vents? You guessed it. All that needs to be done is to run 1 duct from the vent/heat/A-C box to your carb. Now for those who have functioning A/C you have a potential for even more.

Think about it.

If you have doubts try crusing down the highway with your windows up and the A/C off.

Cowl Induction is better than ramair. Forward opening Pro Stock hoodscoop is better than cowl induction.


------------------
'88 IROC TPI 355, '69 truck 4-bolt, fully balanced, 9.75:1 compression, fully ported '70 truck heads(for now), Harland Sharp 1.6 Roller Rockers, Comp Cams CS 252AH-12, ported '86 TPI converted to speed density, Crane AFPR, Flowmaster 3in. exhaust, Edelbrock TES headers, all emissions equipment is still intact, plan on burning my own chips, many more mods and parts on the way as time and money permits =(
Best E.T. with TBI 305: 16.11 @ 82mph
Haven't been to track with new motor
If you have any questions on converting from TBI to TPI email me at jdkchevy70@yahoo.com
In memory of Dale Earnhardt, I'll miss cheering for that black #3 on raceday!!!

A properly designed Ram Air setup will outperform a cowl induction setup any day. The reason is the pressure at the base of a windshield is partially determined by the rake of the windshield. With Ram Air it's like running the air into a vertical wall, more pressure. Blah, Blah, Blah! It just doesn't matter on a street car much just go with what you like the best.
Da Freaky - I guess you're telling me the fan has nothing to do with the air flow out of my AC, yeah right!

[This message has been edited by FlashGTA (edited April 19, 2001).]

Yea! I'm saying just that!!! Put your AC "lever" in the "off" position and roll your windows up next time your on the high-way. It's call flow-through ventilation and the air is taken in from the base of your windshield - Ah-la cowl inducted. Why do you think there is a screen on the top of your firewall by the wiper arms? It's not for decoration, I know that.

If you have a functioning AC on your car and run a duct from the inboard (engine) side of your evaporator housing to your air filter you can get VERY cold air into your engine! The fan motor will give a minor (very minor unless you completely block off your vents) blower effect.

Without a fuctioning AC you will only get air the temp of what's outside you car (the same air temp you get through your vents).

On non-AC equiped cars I don't think I'd try this because the heater core would be too close to the area you would have to duct from, there-fore no benefit would be negligable.

Seriously, I'm gonna try this when funds permit (currently I'm in the middle of buying a house and moving so all extra money is spoken for). Currently I have a Tri-flo air cleaner on my '82 Firebird and the air temp at the front of my cleaner is 120 to 150 degrees! and that's at night! I haven't taken readings during the day yet but it can't be cooler.

Any other ideas out there???

I know this is an old thread, but I wanted to run my plan by some of the guys who know a thing or two. After I get my 383 put together I'm gonna slap a Weiand 142 on top so I'm going to have to get either the cowl or ram air. I was thinking to myself "Self, why dont you get the cowl induction hood. Just keep the stock hood, cut a hole in it, and slap on a scoop from up22.com? That way you can adapt to the seasons." I don't want to mess with the whole fiberglass to sheetmetal nightmare or the tacky "rivet on scoop" look, so I'd just get one with an inside flange. I'd also get a http://www.summitracing.com/parts/MOR-65960/

I've never seen anyone yet with a ram air type hood with a blower. Not that they don't exist, I just have'nt seen one.

In general, you need at least a 3 inch cowl hood to fit about any roots blower with an air cleaner. I have a 4" steel cowl hood, and my air cleaner is fully inside the cowl, but I'm not running a 142. Most of the functional cowl hoods sold have a hole cut in the underside where your air cleaner pops through. But I suppose you could get a non-functional cowl hood and make it functional with one of the square air pans you posted.

I'd suggest taking careful measurements AFTER you install the blower and research what size hood you'll need.

I think it's more on personal preference than function. I don't think we run fast enough for either to gain that much improvement. If that were the case aftermarket hood companies would be clamoring to claim HP increases with their hoods. As for my ram air hood, i bought the car with it already on. If i had my choice i would have gotten a cowl like this, http://www.hawksthirdgenparts.com/ca...turbohood.aspx Just my opinion of course.

Actually, it's not a matter of personal preference as much as it is what fits.....and what you posted is I believe a 2" cowl, which would be a big mistake. And if it turns out to be 3", it may barely fit......

While we are back on the subject Joe Sherman has posted many times that he has made more horsepower and faster track times with a properly desiged "ram air" hood versus the cowl style. With the ram air hood you have to be careful that the air just does not blow through the air filter. No personal experience in this just what I have read.

Actually if you look, it looks to me like a 4" cowl, you also have to be aware of the 4" or greater law on hood hight in some states. As far as what fits, you can make anything fit with a little finesse and patience.

Looking forward to seeing it then! Post up a pic when it's together.

EDIT: Ooops....red rock - I see you're not the one trying to stick a blower under that "IROC Turbo Hood" aka "Daytona hood".....that's what I'd be interested in seeing. I'm sure that hood would clear a tuned port...ain't gonna happen with a blower though.