seal cowl induction?

[PaulL]

We all know the Viper hood has about a 2" cowl induction opening in the back. After doing a lot of reading, the higher air pressure caused by that can affect the cooling of the radiator. Would it be beneficial to attempt to seal this opening? If so, what could be used (i.e., maybe some kind of large seather stripping)?

Discuss.

[BigTyla]

Don't know where you read that, but that couldn't be more wrong. At speed, there will be LOWER static pressure across the hood, creating a vacuum effect that will pull the air from the engine bay out through the duct.

[PaulL]

Don't know where you read that, but that couldn't be more wrong. At speed, there will be LOWER static pressure across the hood, creating a vacuum effect that will pull the air from the engine bay out through the duct.


I agree. I have a Seibon hood and 2 problems we have identified are 1. I can fit my hand between the cowl and weather strip by the wind shield and 2. the rear vent is an intake, so at speed causes the pressure in the engine bay to rise. This means that the fans can't pull any air through the radiator. Even in neutral the temperature doesn't start to fall off until my speed drops to say 40 mph!

The first problem may not sound like a problem until you realise that the air by the cowl reverse flows back into the engine bay rather than going up and over the car. You can test this quite simply by taping a few short lengths of wool to the back edge of your hood and watch to see if they get sucked towards the engine or up the screen whilst driving.


post #14
http://www.3sgto.org/f13/overheating-td05-turbochargers-6158-2.html

That's not the only time I have ever read about this either. I have read that the bottom of the windshield contains the most pressure, and the easiest place for the pressure to dissipate is through the rear vent. I've never tested this myself, but I have read a lot of articles about this.

[PaulL]

More from other people on other forums about cowl induction


I hooked up a home made manometer using water and clear tubing to measure pressure delta between engine compartment and the cowl. Indeed above about 35, the cowl was in an area of higher pressure than the engine. With the AC on this speed increased to about 45 due to the pressure from the fans. Never was the pressure significantly higher. Not more than about an inch of water at 70.

That little experiment always made me wonder why the majority of folks adding padding to the seal between hood and cowl noted a reduction in vent temp. Like GTX said some is better than none and it's likely the air there is indeed cooler....



The padding helps keep engine heat and smells out of the HVAC intake when the car is slow. The padding returns the rubber cowl seal to original shape and function sealing the cowl away from the engine compartment. (Not all parts on Miatas age gracefully?) I consider this a good thing and a civilizing influence on my driving experience. A good firewall/hood seal also keeps the cowl higher pressure air from 'backwinding' the radiator at speed. The last thing a radiator needs in some other high pressure air coming into the engine compartment to lower the radiator's pressure differential before and behind it.
Jacking the rear of the hood to create a large permanent gap does just the same thing at speed. Terrible for cooling going fast. Great for engine ventilation when stopped or very low speed.

[BigTyla]

If they are doing as they say then it isn't a cowl at all or is a poorly-designed one. If the cowl were too large or at too large an angle of attack I can see this occuring. It would also occur if pressures under the hood were low, which could be caused by poor ducting and/or missing splashguards.

EDIT: I will say that I could definitely see this being an issue if the cowl opening were too close to the windshield. That is a significant area of fluid stagnation.

[anyonebutme]

If they are doing as they say then it isn't a cowl at all or is a poorly-designed one. If the cowl were too large or at too large an angle of attack I can see this occuring. It would also occur if pressures under the hood were low, which could be caused by poor ducting and/or missing splashguards.

EDIT: I will say that I could definitely see this being an issue if the cowl opening were too close to the windshield. That is a significant area of fluid stagnation.

"Cowl's" by design are intakes. It would have to be about 8 inches forward of the hood trailing edge at least to become an extractor.

For the visual crowd:

http://i1145.photobucket.com/albums/o503/valitonn/front.png

http://i1145.photobucket.com/albums/o503/valitonn/split.png

[BigTyla]

Semantics I guess. I've always thought of cowls as extractors and being significantly upstream from the windshield. I've never known of a cowl to be referred to as an intake device. Those are usually called ducts in my realm of engineering.

[PaulL]

Regardless of semantics, the viper hood is raise someting like an inch or two in the back. By your terminology, it appearantly serves as a duct being at the bottom of the winshield. Is it better to seal it off?

[anyonebutme]

Semantics I guess. I've always thought of cowls as extractors and being significantly upstream from the windshield. I've never known of a cowl to be referred to as an intake device. Those are usually called ducts in my realm of engineering.

"Cowl" is not the duct itself, it's the location proper. Any duct device is the cowl is an intake due to the static pressure developed in the region.

Best examples I can give is the intake system of a NASCAR type cup car. Or any 60-70s domestic fitted with the hot new thing of the time: Cowl Induction.

Anyways, it's a very basic principal that's still used in vehicles today, mostly to force air into the HVAC system without the use of the fan for the fresh air input for the mixing box.

[BigTyla]

I know how it works. It's my job to know. :p I was simply referring to the semantics.

[BigTyla]

Actually come to think if it, I do partially disagree with your assertion of it functioning as an intake, but perhaps this is application-based only. Cowls can be induction-based or designed to extract hot air depending on their location, lending to my previous comment above.

If we're talking about the massive hoods with openings at the back near the windshield then I absolutely agree with you.

[BigTyla]

Yeah, definitely overlooked your particular application, Paul. With your hood the air will be coming through the cowl due to its proximity to the windshield as I specified in an earlier post. It would be best for you to seal it.

I confused myself as I immediately thought of the hood with the cowl in the middle instead of far back. Im looking at something like that foe my setup. A lot of high performance cars will actually duct the air from the front mount intercooler and radiator and completely seal it to tge cowl in the middle of their hood.

[anyonebutme]

Actually come to think if it, I do partially disagree with your assertion of it functioning as an intake, but perhaps this is application-based only. Cowls can be induction-based or designed to extract hot air depending on their location, lending to my previous comment above.

If we're talking about the massive hoods with openings at the back near the windshield then I absolutely agree with you.


?

cowl - definition of cowl by the Free Online Dictionary, Thesaurus and Encyclopedia. (http://www.thefreedictionary.com/cowl) look at #3. Location of the "cowl" is fixed. If it's in the middle of the hood, then obviously it's not a cowl, it's an extractor.


If it's your job to know, you're doing a shit job at it, lol.

[PaulL]

Yeah, definitely overlooked your particular application, Paul. With your hood the air will be coming through the cowl due to its proximity to the windshield as I specified in an earlier post. It would be best for you to seal it.


That's what I was thinking. I guess I will need to find a thick piece of weather stripping. Any advice on what to use?

[PaulL]

Just thought of this. If I am able to use something to seal it up, what if I didn't completely seal it off all the way across the back of the hood. In other words, since the highest presure is central to the cowl, what if a little bit on the sides is not completely sealed up to leave a little room for venting when at a stand still. Good idea or bad idea?

[BigTyla]

?

cowl - definition of cowl by the Free Online Dictionary, Thesaurus and Encyclopedia. (http://www.thefreedictionary.com/cowl) look at #3. Location of the "cowl" is fixed. If it's in the middle of the hood, then obviously it's not a cowl, it's an extractor.


If it's your job to know, you're doing a shit job at it, lol.

Careful buddy. I'm referencing the physical mechanisms you were talking about, not the semantics. Your explaining very basic fluid mechanics to an aerospace engineer. Forgive me for not being enthralled with your wisdom. No need to get personal.

Paul - your idea might work. Only way to know short of some ridiculous CFD testing is to try. Weather stripping would work great.

[PaulL]

Paul - your idea might work. Only way to know short of some ridiculous CFD testing is to try. Weather stripping would work great.

Well scratch that idea, its sealed off towards the sides. Now i've just got to find some thicker weather stripping.

[BigTyla]

There ought to be some foam-type substance you can use from Lowes. Or you could just raid LKQ for some stripping. My Explorer and 350Z both had sealing strips from the factory that would work great.

[IPD]

paul,

my $.02:

you want a vented hood--hood intakes (cowl or otherwise) are a bad idea--for our cars. you want all the airflow you can possibly get to go through your intercooler & radiator. you want to syphon that hot air out of the bay as fast as you can. any form of additional airflow into the bay will reduce how quickly said how air can be expunged.

[J. Fast]

Regardless of semantics, the viper hood is raise someting like an inch or two in the back. By your terminology, it appearantly serves as a duct being at the bottom of the winshield. Is it better to seal it off?

Tape some yarn, tuft wool, or caution tape (cut into 1/4" X 6" strips) to your hood every 12" on center in the field and every 6" on the perimeter and post up how the air is moving. Use backer rod or garage door gasket to temporarily close off the cowl and repeat the test. Prove the problem and then come back to discuss a fix.

... All this time to type winded questions for 5 minutes of your time and $5 worth of scotch tape, string, and gas for an empirical answer? Time waster, really.

[BigTyla]

I'm almost certain Paul has splashguards installed else he wouldn't be so persnickety about the subject at hand.

I also agree with IPD about the hood vent. It's a much better solution for the problem at hand (FMIC, large and hot turbos) than a hood with a rise in the back. I'd love to see a fully-ducted solution that vents through the hood vent, but that's probably just me loving the overboard solution for a street car. :)

[PaulL]

paul,

my $.02:

you want a vented hood--hood intakes (cowl or otherwise) are a bad idea--for our cars. you want all the airflow you can possibly get to go through your intercooler & radiator. you want to syphon that hot air out of the bay as fast as you can. any form of additional airflow into the bay will reduce how quickly said how air can be expunged.

Thanks for the input. I had bought this hood probably about 6 or 7 years ago and sold the stock hood. I have not driven the car very much in that time frame. It seems that at the time of purchasing, no one really mentioned anything about the slight raise in the back to be a bad thing for these cars. I don't want to spend anymore money on a new hood, so I'm kind of stuck with what I have for now.

[QUOTE=J. Fast=Tape some yarn, tuft wool, or caution tape (cut into 1/4" X 6" strips) to your hood every 12" on center in the field and every 6" on the perimeter and post up how the air is moving. Use backer rod or garage door gasket to temporarily close off the cowl and repeat the test. Prove the problem and then come back to discuss a fix.

... All this time to type winded questions for 5 minutes of your time and $5 worth of scotch tape, string, and gas for an empirical answer? Time waster, really.[/QUOTE]

Been working on the car for the past week or so. It hasn't been drivable for me to take it out and try it. There is some good information in this thread, so I will have to respectfully disagree on the fact that it's a time waster.

[PaulL]

Are you actually overheating? If not, why bother sealing it if your engine temps are fine.

Are your main splash shields (aka - front spoiler for VR4s) in place? Radiator cowl in place? Those are a lot more important to overall proper cooling/air flow than your hood yet so many leave them off or do not replace when damaged.

Splashguards are installed, no radiator duct now as I have an FMIC. Car temp is fine when the a/c is turned off, about 193 degrees at interstate speeds. Temps are based off innovative G3 temp gauge in the t-stat housing. Temp starts very very slowly creeping up with a/c on over time, but I haven't had a long enough duration of driving the car to see how absolute high it gets. I really haven't had much time to take the car out for testing. Once I was driving with the A/C on and a CEL was thrown. Temp gauge read about 200 degrees, it was 85 degrees outside. I turned the A/C off, and a minute later the CEL went off. I later turned the A/C back on and didn't see the CEL come back on.

One thing I did notice yesterday was my t-stat housing cap is old, and the seal had some small cracks in it, so there may have been a bunch of air pockets in the cooling system. I put a new stant cap on yesterday and bled the coolant system so I am planning on going out for a test drive the next chance I have to see what the results are.

[PaulL]

I'm almost certain Paul has splashguards installed else he wouldn't be so persnickety about the subject at hand.

I also agree with IPD about the hood vent. It's a much better solution for the problem at hand (FMIC, large and hot turbos) than a hood with a rise in the back. I'd love to see a fully-ducted solution that vents through the hood vent, but that's probably just me loving the overboard solution for a street car. :)

I thought I saw a picture on som other forum with a DSM that was working on that solution. It looks like he had vents right behind the radiator, and made ducting for the air coming through the radiator to go right out of the vents.

[IPD]

I thought I saw a picture on som other forum with a DSM that was working on that solution. It looks like he had vents right behind the radiator, and made ducting for the air coming through the radiator to go right out of the vents.

if you're familiar with the DSM scene at all, you've probably ran across gixxerdrew's hood for 2g's. i tried throwing together a GB for a limited run of that same type of hood for the 3/s...but never got any nibbles.

[PaulL]

I might have run across it, but I'm not familiar with the DSM scene. I just found a link someone had posted on 3SI while I was doing a search and saw it then.

Well, I went on another test drive, and posted the results in the other thread is was posting in
http://www.3sgto.org/f13/overheating-td05-turbochargers-6158-5.html

Its about all of the time I had to test drive today, but hopefully I can get all of these cooling issues worked out this summer without having to remove the FMIC.

[IPD]

- DSMtuners Gallery (http://www.dsmtuners.com/gallery/browseimages.php?do=member&imageuser=84613)

i'm 100% certain that if he'd built a hood for our platform, it would be the best hood ever offered by anyone. ever.

[stealthee]

Except for the looks issue.

Like it or not that is why you didn't get any bites. If you like your choice of hood, fine, but don't get pissy because no one else does.

[PaulL]

Except for the looks issue.

Like it or not that is why you didn't get any bites. If you like your choice of hood, fine, but don't get pissy because no one else does.

I am confused at who this is directed at?

[stealthee]

Its directed at IPD. He tried to get a Group Buy going for that hood for a 3s and got no interest. The reason he got no interest is because the styling does not fit the 3s styling.

[PaulL]

Its directed at IPD. He tried to get a Group Buy going for that hood for a 3s and got no interest. The reason he got no interest is because the styling does not fit the 3s styling.

Ahh, I missed that thread, which is why I was confused by your comments.

[IPD]

Except for the looks issue.

Like it or not that is why you didn't get any bites. If you like your choice of hood, fine, but don't get pissy because no one else does.

brian, everyone is well versed on how much you dislike this style of hood vent--just as they should also be aware that it offers better functionality than any other style currently offered. i wouldn't really expect you to appreciate the function > form thing, as you've never suffered the high bay temps from a turbocharged 3/s.

for the record, the ultimate design of the hood was open to discussion--but with the proviso that it have maximum cooling effectiveness & that it wouldn't clash horribly with the external contours of the 3/s. gixxerdrew's design also improved downforce--which is something no other existing hood offers.

the fact of the matter is, the GB didn't succeed because this is the 3/s community. i've seen COUNTLESS GB's go nowhere because that's how this community rolls. people want something more than is currently offered. when something legit IS offered, people fail to pony up and put their money on the table. happened to engine dampers and a host of other parts.

people would rather bitch about cianci's quality going in the shitter and/or a lack of a good alternatives, rather than seek out something with a proven ability to 1. add downforce 2. trump all other forms of cooling the bay via the hood. it's not about looks, it's about how the ownership of this platform rolls. just like how west-coast 3/s owners complain about the NG not being there--even though they never put their money where their mouth is.

it's got very, very little--if anything--to do with looks. you're projecting, man.

p.s.
i don't hear you ragging on the guys who cut their bumpers for better airflow either.

[BigTyla]

Yes, Paul, the DSMTuners thread is exactly what prompted me to think more about the issue. Of course, IIRC, that guy is a devout road racer and his solution is mainly to meet that end. The problem with these cars is that making a ducted setup in an already cramped engine bay would prove to be difficult.