Cooling ducts to cool underhood?

[Ken]

... the base of the windshield is normally an area (of) positive air pressure. My opinion is ... if it is removed or has openings cut in it then the hot air coming through the radiator will easily over-power any air trying to come in at the top of the hood.

Nope.

In the pressure contour, it can be easily found that there are positive pressure areas at the front of the body, especially in the area before the radiator and the boundary area between hood and the front windshield. However negative pressure area is also found at the front end of the hood. Both the front and rear end of the roof are negative pressure areas. Those results agree to the experimental results in TJ-2 wind tunnel. There are no obvious negative pressure areas at the tail of the model, which is different from the wind tunnel result. This shows that the model should be amended. In the velocity vector, it can be seen that there are small separation sectors in the areas above the radiator, near the bumper, and above the front and rear windshields. And some eddy flow is found in the wake of the body. In the area near to the symmetric section, air flow is parallel to ground while it is apart from the roof, and slightly deflects to both sides. Air between floor and the ground goes upwards while leaving from the body. The main direction of the wake is upward. In the areas near to the sides of the body, air from the bottom is whirling and a large eddy is found (shown in figure 4). air from the roof of either side whirls softly, it forms rather small eddies, which are not obvious.

For more information regarding pressure areas on an automobile, and to view the image associated with the text, see Numerical Simulation of the External Flow Field Around a Bluff Car.

(Adobe Acrobat is necessary to view it.)

_ken

 

[Mad-Mic]

only reason i am interested in doing this is not just driving but more sitting or when the car is off. i don't like to leave my hood open just to let the heat escape at the track. it would just be nice so that the hot air can escape faster than what we got going now for us.

i'm gonna work on my this week and see what i can come up with.

 

[Hotred94]

Interesting study Ken. Thanks for keeping us on our toes. After looking at it, I am still inclined to believe that it is true only if the air from under the hood is blocked off, and if the rubber seal is removed, the hot air inside the engine compartment will over-power the air trying to curl around the base of the windshield.

Not to squabble or anything, but it is indicated in the study that they are simulating external airflow over a solid block model only; that is, they are not accounting for any air passing through body cavities such as the front grill. So long as the rubber hood seal is in place, preventing airflow in either direction under the hood, then the airflow over a real car will act as if the car were indeed a solid block because underhood flows have been routed elsewhere by the seal and will not interfer in any way with the pressure area at the base of the windshield. It is reacting to external flows only.

With the rubber seal removed, underhood influences must now be accounted for. Figure 2 in the study shows pressure gradiants on the model--just what we would expect. Figure 3 shows velocity vectors, which perhaps might be confusing with air pressure. What velocity shows is of course the speed of air, in this case, moving around a solid block. It is understandable that there will be areas of negative velocity and pressure at the front end of the car (especially a solid model) as the air is forced to go around the model. This causes compression, decompression, and eddies. and high velocity as the air must move faster than the car to get out of the way.

So the ultimate questions will be, Is the air pressure under the hood higher that the air pressure at the base of the windshield? And when the rubber seal is removed, which one will over-power the other? A simple experiment will answer this question. Remove the seal, place some short streamers between the intake vents and where the seal was, then take a drive and see which way the streamers flow. Make sure the streamers are short enought to not be influenced by laminar flows coming over the hood or eddie flows as external air moves out of the way of the moving windshield. I may try it this weekend.

Thanks

 

[Ken]

I may try it this weekend.

Cool, then we might have a definitive answer. :cool

I can just see you now -- running up and down the street in front of your house with streamers attached to your Corvette's hood, driving your neighbors crazy. :L

_ken

 

[rrubel]

I can just see you now -- running up and down the street in front of your house with streamers attached to your Corvette's hood, driving your neighbors crazy.

I want a picture of that!

So speaking of airflow under the hood, has anyone ever considered replacing the accordian air coupling from the MAF to the TB with a small intercooler? Maybe with a cone filter in front instead of the airbox, it would fit better. Somehow you'd have to get airflow across the top of the intercooler, but something like one of those intakes that replace the front license place should be good for that, right? Or the brake-duct coolers that started this thread...
[RICHR]

 

[Mad-Mic]

ok i measured 1 1/2 inch from the stock intake flange where the distributor is and measured back off that 8 inches cut down 1 1/2 inches and notched it out. i could definetly feel the heat coming out of it when i shut the motor down at 200 degrees water temp. next i am gonna fabricate some sheet metal and add it in there with a small wing coming off of the rubber piece to the end of the hood. actually it will stop short of the wiper arms so the heat will be elevated to move up and not back down.

i'm not sure how well this will work driving but stopped it definetly works great so far!

 

[Hotred94]

Well I just spent 5 hours Saturday changing spark plugs (well, okay, I ate lunch too). I finally ended up unbolting the ASR and moving it back to get access. Finally got it done while breaking only two plastic pieces on the engine in the process. So I didn't get a chance to run up and down the street with the streamers under the hood. :CRASH

That intercooler idea is something new. IMHO, I kind of think you would be better off with cold air at the filter right to start with. The temp gradients aren't viable, but you are on to some good science.

I was looking at a Ricer magazine the other month and I saw an article where they compared something like 22 intake filter setups on a dyno. Every single filter was a cone type connected to a custom bent tube that twisted around the engine compartment and ended up at the engine intake. Dyno results varied but the setup that produced the highest horsepower was not the one that flowed the best, but the one that picked up the coldest air.

Everything in the vette is so tight, I wonder if hood grills would be effective.

 

[WhalePirot]

bought the kit from Mid America. Was disappointed

It's going back, too.

I doubt that the tubes will: 1) fit properly to allow ducting into the engine compartment, and 2) that it will be effective at all, except at speed. Any air flowing in thru the 2 1/2 tubes will likely be overpressured by other sources. I won't cut holes in my underfender areas to try this.

Now, I will wrap my headers and exhaust pipes all the way to the CAT. After doing this to my last set of headers, I noticed a definite power gain but could not quantify the heat reat reduction.

I just wrapped my (mini-ND) starter as it was struggling (or failing) with the underhood heat.

I may put a 10" fan in my left grille to pull air out, as my battery is inside the car and the 2 1/2" thick fan will fit. Doubtfull there is enough room on the right side. If there is still a problem, I may fit one or two 7" fans in the '84 hood, to ring air into the ductrs which used to take air to the TBs from just afore the radiator.

I won't put small fans in the wheels wells, just in case is DOES rain in SoCaliornia and my car happens to be out driving. I appreciate the brain storming, guys.
mike

 

[bill mcdonald]

I'll be watching this one as well.

 

[94conv.]

my 94 is completely unmolested and does not have the rubber seal behind the hood latch, my 89 did have them. At some point in between the factory took them out to.

 

[oldace84]

So the kit is ready for and has parts for cooling the front brakes....I have it from Mid America......but haven't installed it yet.....great for cooling the front brakes....
tony

 

[WhalePirot]

Heck, Ace. I could've saved us both some bucks by dropping it off!
mike"v

 

[Ken]

Anybody who thinks about hood scoops for a C4, let's brainstorm...

BRAINSTORM!!?? Moi? :L

Ofttimes, we talk amongst ourselves about underhood temperatures and cool air intake for our beloved fourth generation Corvettes. Let's do it again! :gap

Callaway Owners, obviously they found that there was a better source for incoming air to the turbos when they changed from the "NACA-style" (now NASA) ducts in the hood to the top of the front bumper, but were the NACA ducts very helpful? For that matter, did they work on the old Mustangs?

Which style of cool air intake is better, the force-fed air from the front, or pulling air from the high-pressure area at the base of the windshield? You see both, or at least you used to see both, at drag strips on the Pro Stockers. They would either run the forward-facing scoop or run a scoop almost flush with the face of the windshield, running about halfway up.

Early Shark People, the L-88 style hood: does it vent hot air from the front, as well as take in cool air from the rear? Seems possible, but I have never seen one up close, (or paid attention when I did) believe it or not. :confused

Obviously, I am still thinking about a customized hood for my Corvette.

 

[Edmond]

Ken,

I thought about this before. I think that the force fed air wouldn't really be much of a factor unless you're up to a significant speed (at least 60mph?).

As for the pressurized area near the bottom of the windshield, will water get in there?

How much can we really gain by employing a hood scoop on the C4?

When I think of a hood scoop, I think of the Camaro Z28 vs. the SS. I know that the extra few horses aren't entirely attributed to the large hood scoop on the SS, so how much did the scoop contribute to the extra horses?

Would you get the same results with a C4 scoop? How about a way to extract the hot air from the engine compartment? I always thought that the side "gills" could've used some improvement.

 

[BigRed]

I think with the new fuel injection models that the hood scoop's are purely cosmetic.

The air being fed into the TB as you know, is through circular plumbing leading to the front of the car. Now how exactly are scoops going to help the engine?

I have seen a funnel ram available that gets inserted into the current front license plate location. That connected to the intake plumbing will be beneficial at higher speeds.

As for the cooling factor advantage with scoops....Water wetter, Bcool radiators, dual electric fans, and higher flow water pumps seem to be a better and more functional answer. 160 Degree thermostats and Chips help to.

Ken Im pretty sure you have all of the above installed on your car except the funnel ram. If I were you I'd consider a more direct approach to getting air to the intake. If your new engine isn't having clearance problems (Actually it looks smaller LOL) leave the hood alone.

The Ol' Chevelle days were carbs and round open filters grabbing air from anywhere they could and thats why they actually had a function. Today not so much.

(Of course Im not talking about direct feed turbo's or superchargers.)

IMHO of course

But hey they DO look cool :t

 

[Ken]

But hey they DO look cool.

You got the idea!

 

[WhalePirot]

underhood temps, air intake temps, or looks

What is your goal? Looks is one thing; performance is another. What do the racing guys do and how doe their driving differ?

As you know, I am seeking a cooler underhood environment. I looked at usinging the MidAmerica front thingy, fed through their spoiler. I decided that it would do me little or no good, as the fan would pull air into the area and likely overpressure any such ducts. It went back.

Now my approach is phased. FIrst I will reduce the problem by wrapping my headers, as far down as possible. I know the effectiveness of this from my last set, in both underhood BTUs and thermal efficiency; yeah, I have felt how much better they work. Carb guys are advised in ThermoTec literature, to readjust, as the headers scavenge better; leaning out the mixture more than naked headers did.

Next, if needed, I will mount a 10" exhaust fan in the left gill. My battery is not there; my oil filter is, which leaves a lot less restriction to airflow.

The '84 hood has ducting, which I may use to bring air, from 2 or 3 new 7" fans mounted front of the radiator, through to the former TB feeds. This should blow air down onto the engine.

"fuel ram inserted in place of front license plate"<< I was ready to install this, but was told to save my money, as it is virtually ineffective. But then, so are most of the mods guys here really like.

Perhaps for us, Callaway holds some answers. I believe those NACA scoops feed the turbos, not cool the engine. Correct me if I am wrong.

 

[bill mcdonald]

Callaway Owners, obviously they found that there was a better source for incoming air to the turbos when they changed from the "NACA-style" (now NASA) ducts in the hood to the top of the front bumper, but were the NACA ducts very helpful? For that matter, did they work on the old Mustangs?

\

Ken, those NACA ducts were feeding cool air to the intercoolers on the early callaways.
Then later, they ditched the NACA ducts, they picked that air up from under the nose, (just like on an 84) where the air filter is on a stock corvette. the air went up into the hood, through channels/hood reinforcement to the intercoolers.
Then callaway went to the 2 scoops on the top of the hood to feed air straight into the intercoolers.

The Vipers used the Naca on the front of those cars to feed thier air boxes.

C5R (Silver car) has a naca on the roof (near the halo) feeding air to the coolers mounted in the rear of the vette. I am betting they work well. they are suppose to have the least amount of drag on the body.

As for me, I have been wondering how cool it would be to mount the radiator slanted forward, and putting an exit scoop on top of the hood for the air to exit. This would be similar to the C5R, Ferrari F50, or Enzo. I have seen some of the panteras with this mod as well, they said it gave stability at high speed over the front wheels.

 

[Ken]

My goal? I don't need no stinking goal!

:L I stated Mike, that I was still thinking of a custom hood, hence the idea of "brainstorming". I didn't want to horn in on your thread, but if you like we can merge the two to see if we can come up with something together.

Cool (no pun intended) idea about the radiator Bill. Keep us informed. :cool

_ken

 

[WhalePirot]

My thread?

I thought it was YER thread!!