Hood slats to reduce under hood temp?

[paul e]

>>Coming off the highway at sitting at the light is did rise to 140's. Then when I moved off rose to 152'F and then back down to 120 in low speed traffic<<

Ok.. i think this delta between idle and at speed is an important one for determining how well air flow is cooling the area. BTW, regarding those 2 dr rear hood slats, I could be wrong, but I believe they are over the grate area, and would be outside the seal. Anybody whos car is nearby could check.

As to why your temp goes up when you start moving, I wonder if its related to what i saw when giving it throttle. Remember, I went from just 72 degrees while coasting at 40-60 mph (with the probe near the runners and TB) to 91 degrees, and back down when I got off the throttle. But in my case, I never even Approached the idle temperature when the car was moving even a little, with idle being 142 degrees.

[M3TurboCa]

Paul I think the reason as Nick said it because the fan is tied to the engine so as soon as the rpm increase so does the flow of hot air from the rad.

Since I had the sensor much closer to the rad than you I would show a greater increse in temp from a move off.

[paul e]

>>Since I had the sensor much closer to the rad than you I would show a greater increse in temp from a move off.<<

Yes, I see that. its certainly possible. And the reason the fan would be circulating hot air, instead of cooler ambient air is what again? Although, remember, like you but to a lesser degree, my temps went up as I throttled, and went down as i coasted, which would be somewhat consistant with your result even though in my case, it didnt approach the high temps of idle.

[cal_guy19]

M3 -

It looks like your probe location is up against, or very close to the intake manifold, so you're not just measuring the underhood air temperature, you're also measuring the relative temperature of the manifold. The manifold is in contact with the hot engine block as well as full of the hot air that has passed thru the supercharger. Even with all that, it sounds like you cooled the manifold by about 10-12 F. It's sorta like blowing across the top of a bowl of hot clam chowder. The chowder won't instantly drop to breath temperature, but it does cool down.

Uh oh. Suddenly I'm in the mood for some seafood.

[hotghias]

sorry if what i'm about to say is stupid, because i didnt read the whole post- it went off on too many tangents and i don't have time to read 5 pages. but the idea of air flowing out from under the hood by removing the weatherstrip sounds wrong to me. (i think) cowl induction on the old muscle cars works because, at speed, there is a high pressure area at the base of the hood that forces the cold air back under the hood to the carb. wouldnt removing the weatherstrip do the same? maybe the slightly different location changes things. i guess if someone tested it and it worked, it works, so this post was pointless.
later,
evan

[cal_guy19]

Aerodynamics is annoyingly complicated, and usually involves a wind tunnel to determine what's actually going on. But here's my take on what happens. The car is moving along at say 65 MPH, so air hits the front grill area at that relative speed. A little Bernoulli equation diagram, and we conclude there is some extra air pressure in that area of the car, capable of forcing that air to move at 65 MPH against atmospheric pressure. So air goes into the engine compartment at that pressure, from whence it tries to escape. It finds a hole, say under the car at the rear of the engine, and now, with the weatherstripping removed, at the top rear of the engine compartment. So that pressure is able to propel the air out of those escape exits at that same 65 MPH. Of course, the air hitting the windshield also creates some pressure increase above atmospheric, but the windshiled is sloped, so some of that air slides away, and we don't get the full 65 MPH worth of pressure hitting the outside of the removed-weatherstrip-airgap. This difference in pressure from inside to outside, can still propel a substantial amount of air to exit the engine compartment. Of course, none of us really knows how much, since we don't have a wind tunnel or a digital anemometer at our disposal. All we do have are those thermocouple measurements which indicate that much of the area under the hood actually gets significantly cooler when we remove the weatherstrip.

[NickG]

cal_guy, I disagree with your explanation. (Doesn't mean that I'm right, I just see it differently )

The aerodynamics are such that the air 'swirls' at the windshield's base and causes a high pressure zone there. My tests done a few years ago indicated that. Also, the whole basis of cowl induction hoods is based on that.

The air under the car is a low pressure zone, similar to a vacuum. And that vacuum effect can be very large. For example, I once saw on the Speed Channel that a Formula1 car generates so much downforce at speed (downforce = vacuum sucking the car onto the road's surface) that the car could drive upside down (ie, on the ceiling of a tunnel) and not fall.

Combine the high pressure zone of the windshield base with the low pressure zone of the underbody, and I think air ENTERS the engine compartment when at speed with the weatherstrip removed.

Now does it help the temps? Probably, and that's what counts.

[got psi]

Why don't you tape small streemers ,in the cowl area. It might tell you which way the air is moving. If it is going back under the cowl due to high pressure the streemer should follow and visa versa. Just a thought brought on by the mention of aerodynamics. J.T.

[cal_guy19]

I wouldn't have believed it if I hadn't seen it myself. I taped a small streamer made
of that very thin teflon pipe tape to the cowl area with a piece of electrical tape. I taped it near the middle of the cowl, then I took off. That damn piece of tape actually got sucked into the underhood area. Nick's description is right - air ENTERS the engine compartment where we removed the weatherstripping rather than exiting there. Somehow, it does seem to manage to provide some cooling anyway, but I felt a lot better when I was under the impression that air flowed in thru the front, thru the entire engine compartment, and out thru the rear.

Anyway, a couple more reputation points for Nick!

[paul e]

>>air ENTERS the engine compartment where we removed the weatherstripping rather than exiting there.<<

So, the low pressure area Under the car is sucking the air in through the removed molding, where the air rushes in on its way to the quickest path to the underbody! I never would have thought this was happening... Which would explain, then why when placing the probe on top of the fuse box within a foot of teh removed molding, that it so quickly registered ambient; its because of the near access of the air from the windshield base hi pressure area.. Whod have thought! But I still wonder, whats happening to the air entering, under force at speed, through the front grill, seem gaps, bumper allowances and so forth? One thing that would be interesting to see perhaps you guys know about.. Our hoods fit tight, but what about loose fitting or ill fitting hoods... At speed, with air entering the front, do those hoods tend to LIFT as under pressure , or be sucked DOWN as under vacuum! And, does this change when the molding piece is removed?

And, what about when the probe is placed on the inside front of the shock tower. .I mean, thats quite a way from the removed molding; its much closer to the entering air from the front grill..Where is IT getting cooled from? Heres something else to consider... Lets think about Nicks' underbody vacuum reference for a minute. .With such a strong vacuum, wouldnt it make sense that air entering the front grill, once in the engine bay, especially with the rear moldings in place so as to maintain the seal, would rush to fill that vacuum by heading down via the quickest route possible to the bottom of the car, through all those access passages in the engine bay.. And, if that were happening, than youd think this would set up its own cooling circulation, and if that were happening, the probe should have registered some cool engine temps with teh molding in place equaling that of when the molding is removed. .AFter all, air entering the engine bay from the front is pressurized, just as is the air in the hi pressure area at the base of the windshield entering through the missing molding!!!!

I dont know if we'll ever know the complete story without better instruments to see whats going on.. but what counts is what we can measure, and what I measured was a drop from 142 degrees at idle to 70 degrees at speed. Wherever the air is coming from, its cooling the engine bay, and thats what we care about.

[frayed]

Oil temps. That's what really matters. Since removal modifies the original design paramaters, and there's some 'new' airflow, not necessarily more, and if more, not necessarily more effective for engine block cooling.

[M3TurboCa]

After looking between the windshield and hood I know why there was not that much air flow from me removing the center I could not see any air gap once I removed the center seal. The hood insulation comes in contach with the car.

So I decided to remove the strip where Paul had his near the fusebox. Once you close the hood you can clearly see a 1/2" gap where the seal was.

Air would definately flow through here now.

The outside temp was 50'F shown by the car.

Driving aorund at a low speed 45 to 50mph I noticed that temp was around 87-90'F

Went on the highway and drove at a steady 80mph temp 104-105'F for a few minutes

Came off the highway installed back the seal and drive back on the same highway guess what the temp was the same 105-106'F. I do not know the reason for this ??

Driving at low speed 45-50mph the temp was higher 108'F

[paul e]

>> installed back the seal and drive back on the same highway guess what the temp was the same 105-106'F. I do not know the reason for this ??<<

Just from looking at the picture, it looks to me like your probe is stuck down in between the runners, ie, where its not getting any airflow. Try moving it to the inside front of your driver side shock tower, near my #2 probe picture shows it... I had a 70 degree temp drop there between idle and speed.... If you move it, try reading the temperature at a steady state 60 mph cruise, and then at a 60 mph coastdown. My temp dropped 10 degrees between throttle and no throttle at that speed. But either way I found it to be pretty effective.

Also, if you just want to check to make sure there is air flowing through the gap you made(direction seems to be reverse of what wed expect, but, hey, fresh air is fresh air! ) just tape the probe to the top front of the fuse box, making sure its sticking upward into the air... On mine, temps dropped precipitously to exactly ambient when driving

[cal_guy19]

I agree with Paul. The idea is to measure the temperatures of the air under the hood, not the temperature of the engine block or manifold itself. Set up the probe so the tip of the probe (where the 2 thermocouple wires are joined) into the air itself, at least
3" away from the nearest structure.That is the air that will be circulating over those hot engine components, removing heat.

[M3TurboCa]

The probe tip is sticking up in the air on top of the manifold..

Why would you not want to se if air around the manifold is being reduced?

[paul e]

>>Why would you not want to se if air around the manifold is being reduced?<<

Its not that you wouldnt want to see it there. Its that with the probe tip buried between runners, youre not measuring air thats being subject to the air flow. Besides, I think it would take an awful lot more airflow than we're able to give it, either with slats, or missing molding, or whatever, before the air Inside the manifold (or supercharger, or SC discharge pipe, etc) is likely to be effected much. Given the extent to which the SC compression is heating up the intake air, I just dont think we should be expecting 'miracles' from this fresh air overwash; after all, its NOT an intercooler All Im hoping for is perhaps a longer life of hoses and other materials, and some cooling of the outside of other underhood components; I really wasnt expecting to see IATs drop much.

[M3TurboCa]

Paul I understand, I thought you guys were interested in removing heat from all over the engine compartment.

If I can reduce overall heat from under the hood then I'm interested in that.

Hmmm would be nice if one could monitor temp from different points in the engine compartment and compare it with the seal removed and installed to see if temp are reduced all over.

[paul e]

>>If I can reduce overall heat from under the hood then I'm interested in that<<

Sure.. so would we all... I just dont think thats possible. I mean, I think it IS possible to lower the temperature of most of the air, but, even so, I dont think the probe location IM seeing on your pic, down in between two runners, would be subject to that cooling. From what I see, it even looks like your probe is aimed Downwards into that hole which exists in the valley between the two runners. I just dont see how any air influence is going to be felt there. I dont even know if a CF hood with the scoops Ive seen would do much more than what we're doing.

>>would be nice if one could monitor temp from different points in the engine compartment and compare it with the seal removed and installed to see if temp are reduced all over.<<

I think there are tools avaiable which would let you place maybe 3 or 4 thermocouple probes in various parts of your engine bay, and then dial them in one at a time to record their respective readings during the same session. That would be cool

[bigmansM]

I'd hate to be off topic, but i am too tierd to look back in this thread to find out where the louveres? Also are there any issue with rain? Any cowl hoods out there?(is that too american?)

[Jim M3]

I had a friend look at mine. He is an old gear head who had cowl induction cars. He said this is definitely what is going on in these cars. I really think just leaving the center channell out makes a big difference. I didn't measure this scientifically, but I know how my hand burns when the strip is in. If I touch the manifold after an agressive run it is very hot with the strip in. When the strip is out I can lay may hand flat on the manifold. There is a gap in between the lip and the hood insulation where air gets through. I am not city driving though either I am driving out in the countryside.

[M3TurboCa]

Jim I personally think if the center section was out more efficient air cooling will be created.

I know when I removed my center rubber seal and looked between the hood and windshield with a flash light, my under hood insulation was butt up right against where the seal was there was no clear gap for me like you.

I think I may explore the possibility to remove the under hood insulation and trim it back so air flow can be created.

[paul e]

>>Jim I personally think if the center section was out more efficient air cooling will be created<<

Mark, didnt you say above that with the center section out, you saw no gap? Why wouldnt you just remove the section I did, where you yourself Did see a gap, and where my thermocouple measurements show effective cooling in all my probed sites ? With the metal lip there, which the molding sits on if it were present, you have a barrier against the flow of any water that might try to enter. Ive examined the area after driving in the rain, and its no wetter than when the molding was present.

[M3TurboCa]

Paul since I did not see that much temp drop at higher speed from the last test around the fuse box, I decided not to bother removing the strip.

[paul e]

>>Paul since I did not see that much temp drop at higher speed from the last test around the fuse box, I decided not to bother removing the strip.<<

Hi Mark.. yea, I remember.. but didnt we conclude that was because your probe was stuck down between the runners, out of the airflow? Or did you do some other testing you didnt report on.... Did you see better results with the center strip removed? I thought that you saw no gap in that area with the molding removed, meaning air couldnt flow there. .

[M3TurboCa]

Paul I saw a 10' drop from the middle section removed even though the under hood insulation was touching the base where the seal was mounted.

Because the pressure is great enough maybe the airflow gets past the insulation??

Since my probe was in between Num 1 & 2 intake and it showed a reduce under hood temps, then with the under hood insulation trimmed so that there is a gap like when you remove around your fuse box area then, this should create a better air flow and cooling.

If Jim can now touch his manifold all over and its much cooler because he removed his center seal, then this believes me to think with proper clearance and removing the middle seal might provide the greatest cooling effect.

Jim when you look in between can you see a gap where the hood and frame meets where the seal was removed ?? I noticed that you also have a 4 dr.