Never fails that when I start one of these threads, I end up with more questions than I had when I started.

My 2c here:

I think that hood venting is the way to go for serious heat soak issues. It's a uphill battle trying to fight the motor by adding a larger radiator and higher CFM fan if the air is still getting trapped in the engine bay. I'd say that if you can live with the look of a louvered or vented hood, it's easily the best way to improve cooling efficiency of the car.

From a theoretical and practical standpoint, there are limits to using a combination of radiator and fan to cool a motor. One is the size aspect - larger radiator and larger fan is less space in the bay, and there is a limit to how large we can fit of both. Also, CFM doesn't necessarily mean cooler temps.

At my university, we build a small Formula-style car a competition hosted by SAE, called Formula SAE, and I'm part of the engine design team. It's a competition where universities build the car from the ground up - chassis, intake, exhaust, suspension, etc. For reference, the engine we use is a GSX-R 600cc. Google has lots of pictures of different cars - you'll get the idea if you search it. ^^

Something quite astounding that I've discovered while doing design on the cooling system is that the car (moving at an average of 30-45 mph on the track) is actually moving too FAST through the air, for achieving maximum cooling efficiency across the radiator. The solution to this problem is to design a sidepod (like the ones you see in Formula 1) that goes from small to big, back to small. This is to slow down the air. Of course, our motor is directly to the atmosphere, mounted in the rear.

The reason for this efficiency loss is as the air moves too quickly through the radiator, it builds up pressure behind and in front of the radiator, creating a boundary layer that lowers the true amount of air moving through the radiator. One might say: Why not use a higher flow fan to create a vacuum and move the air better? There are two reasons on a car: the first being that you want the air to spend a certain amount of time "inside" the radiator (not too slow where it's stopped, and not too fast that it creates the boundary layer), and second being that in most car engine bays, the bay is sealed enough that pressure builds up regardless. These speed values are different for every car, radiator design, hood design, grille design, etc.

But, of course I concede that a larger radiator and higher CFM fan usually increases cooling efficiency. I just know for a fact that venting the engine bay will, unless you are on the surface of the sun, always increase the cooling efficiency by letting nature do its work by letting heat escape. Also, with a larger radiator and larger fan, you also add weight to the car, and you change the dynamic of the water flow through the radiator, since the water pump is still stock. The reason we shoot for maximum efficiency, while still maintaining a reasonable safety factor, is literally, because racecar. :D Any amount of extra weight that isn't necessary in design, is making the car slower.

Also another thing to think about is that turbulent air and turbulent water through the radiator actually increases cooling efficiency. :tup:

You're failing to factor in the intercooler into that. With the additional flow restriction from the intercooler, not to mention the fact that now you're feeding hot air to the radiator, a larger radiator and a more powerful fan may just be getting you back stock efficiency.

Do those fancy vented fenders I see all over the body/exterior section help at all?

Not one bit for underhood temps.

Yeah we're dealing with a forced induction problem in this thread (or at least, I hope we are). Maybe I should specify that in the title.
If nothing else, this is a good discussion. Just turned out to be more complicated than I thought it'd be.

It's never that easy, especially dealing with aerodynamics and airflow.

if you cut a hole in your hood right where the hood scoop sits, you can technically turn a fake hood scoop into a real one

Well I'd need to make sure it would be functional first. Consensus here seems to be that the scoop shown in that picture wouldn't do much (if anything)

It _probably_ won't do anything but it's impossible to tell for sure without doing some testing.

If the engine compartment is sealed as well as others have said, then trying to force more cool air in won't do much good. Sounds like letting the hot air out is the way to go. I like the idea of venting the undertray and exhausting the hot air under the car but don't know if it would actually work or what side-effects it might have.

Interesting discussion.

Why get fans? Just turn them on at a lower temp right?

Oh of course. I'm just saying in my post that I think the ideal way to improve heat transfer in our cars, and most cars in general is to vent the hood. There's almost no downside - it's weight reduction (hopefully), while allowing massive amounts of heat to vent itself, like Synolimit has experienced. A vented hood will always improve cooling efficiency at the speeds our cars experience.

A larger radiator and fan will help, but like I said - it's more of a "reactionary" solution to the problem, versus a "primary" approach of simply allowing the heat to not form as heat soak and get trapped in the first place. Another factor is also if people are okay with replacing the OEM hood - in that case, a larger rad / fans are required. But for race cars, you won't find one without hood/engine bay venting. ^^
Getting larger fans or more efficient fans will allow more airflow, which in most cases for cars, is beneficial. The OEM Radiator/Fan combination for some people simply cannot keep the car cool at full tilt, and that is where I'm assuming people are having issues, esp. with turbos.

I would like to have some custom vents cut in that are akin to the old 280Z factory hood vents.

Uprev adjusts the temp they turn on. The GTM fans move a lot more air than the stock ones.

Alstann, you're right on the vents being the best way to get hot air out of the engine bay. If there were a vented hood on the market I liked from a functional/aesthetic standpoint I'd start with that. I'm just not a huge fan of the options we have on that front, so I'm going to try adding the fans to the CSF radiator I've got, lowering the fan temperature more and running less antifreeze. If that isn't enough to keep temps stable, then ill start cutting holes.

Maybe that's why I stay cool too. Forgot I put maybe 3/4 a gallon of Moore Cool racing fluid in (left over from doing my WRX) and a bottle of water wetter.

If you don't drive in the winter or live in a below 32 degree state, 100% distilled water and water wetter works nice like in my 600cc SS.

That probably has a lot to do with it. Moore Cool is good stuff. I figure 25%antifreeze 75% water and a bottle of water wetter will do fine. Houston rarely freezes, so that's not a huge concern. I still don't feel completely comfortable at 100% water. I wish someone other than Mishimoto made a lower temp thermostat. I'd like to go with a colder temp one, but I wouldn't run that one if you have it to me.

We freeze - i can't get away with that in Maryland.

It's always good to have at least some antifreeze, even say 10%, because then your coolant smells/feels/tastes a bit like coolant. Really helps with tracking down a leak, or confirming that water found somewhere in the bay is or isn't from your coolant system.

I've always heard that's it's a bad idea to run straight water in an Aluminum engine because of corrosion. Antifreeze has corrosion inhibitors. Or is that another of my out-dated facts?

I've heard that, in addition to seals inside the motor need some of the conditioners in coolant to stay in good condition. Water wetter and similar additives claim to have seal conditioners and corrosion inhibitors so you can run water only, but ill always run at least a little coolant just to be sure.

I'm right there with you on that one. :tup: I don't know if I love any vented hood enough to warrant spending money getting one, and then even more painting it. The Seibon one is my "favorite," but still, I'm a clean and simple guy for cars at the moment. I wonder if there is any plastic shrouding near the windshield we can remove, to allow the trapped air to somewhat escape from the engine bay? I've never looked.

Corrosion does occur to some extent, such as mineral deposits and small amounts of rust on the aluminium. The solution is to run straight 100% distilled water, usually purchased from a grocery store. Of course, in cold climates, this is a very bad idea. :bowrofl:

I'd be concerned about taking the plastic at the base of the windshield out and having air forced in from that direction at speed since its a high pressure area.

It should be one of those "can't do any harm" deals. If the pressure at the base if the windshield is high enough it will block any flow out. If higher than that, it will force a little cold air in. Removing/installing the seal (at least on the battery side) is fairly easy, so it would be worth a try. If it doesn't work, put the seal back on.

Aren't the HVAC intakes at the bottom of the windshield? I'd be afraid of sucking all that hot air into the cabin.

It would be easy enough to test. My concern would be the air coming in at the back of the hood and slowing the air coming through the radiator. Somebody needs to go test it with some yarn and see which way the air goes.

If I weren't letting my engine cool down to check the IAT sensor, I'd make a quick run and check that. I'd like to see if it will allow hot air into the cabin. If nobody else has done it when I finish with the temp test, I'll see what I can do.

I'd love to know. My uneducated guess is that it'll act like a cowl induction hood on a muscle car and let air go in, but I'd love to be wrong. It would be really easy to add venting to that area if it turns out to be helpful.

well it should function, it will be scooping up air, how well it would function is a whole different question

honestly you're better off getting hood vents, ya it will dirty your engine bay but you wont have to worry about rain because most vented hoods come with covers for the vents

Not distilled. You only want distilled! Normal water, bottle, house etc all have minerals in it that will corrode stuff.

When I do 100% water plus water wetter it's really not 100%. I just drain the radiator till it stops dripping. The block, water pump etc will still have regular antifreeze in it so in the end you may have something like 90% water, 9% antifreeze and 1% water wetter.

My guess is that, at speed, the pressure in the engine compartment from the air coming through the radiator will overcome the pressure at the rear of the hood. From what I understand, it's not that much higher than ambient, just higher than other places on the hood.

If air is going into the engine compartment, it will probably not be a lot as it will have to overcome the pressure in the engine compartment.

I'm curious to see what happens. Not that I will have any use for the info, but I find it interesting.

I took all the covers out of my engine bay. The battery and brake master lid and their plastic they clip into but not the rubber seal that seals the hood to the plastic covering the lower windshield. You're talking about that long rubber seal and the plastic at the window right? I left it for concern about backdraft too. I don't think those covers do anything right? Even though they have seals on them as well to keep heat away from the battery or brake master I'd guess.

We've had this discussion before. The base of the windshield is a high pressure area. Why do you think the '70's Trans Am's, chevy muscle cars, nascar, and a few others all use that area for air inlet into the motor. The best idea so far has been synolimit's. It's directly behind the radiator, at the front of the hood. Which is a low pressure area. All you would need is a cover for it that has the opening in the rear of it. Facing the windshield. About 1.5"~2" high. The air moving over it would help suck out the heat from under the hood. Another idea would be fender vents. Think of the '70's Trans Ams. I had 2 of them. The vents on them worked. Because they got their air directly from the engine compartment. Not from the inner fender liner, like some vented fenders do now.

Very cool. Definitely keep us posted.

This is probably the hood many of you would like. It keeps all the factory lines of the hood and just generates 2 parallel lines opening to vent air in the front. For those worried about the weather, even with mesh or a grill, there are other options to consider.

Hood to consider:


Here is an option to protect your engine bay, these are rain guards (came with my Seibon hood), which attach via a few bolts.


Adding those to the hood will give you the ability to block out the hood if you want to protect the engine area or even need to keep heat inside the car for winter reasons. Also giving you the option to remove quickly when you need to.
Also, I ran some early tests with the OEM hood and my stage 1 SC and will be adding a Seibon TS hood later to get a comparative results. Currently waiting to get the hood on and finish the results. http://www.the370z.com/forced-induct...s-testing.html

That looks like exactly what we need.

That is what I am looking to do with my hood. Or vents to go right over the turbo/downpipe or the header area would be useful I would think.

Just got back from running the tattletale test. Removed the rear hood seal. Taped two pieces of twine (some fluorescent pink stuff I had hanging around, the stuff you see used on construction sites to hold a spirit level) to the back edge of the hood where the creases in the hood are and another to the wiper arm (centerline of car). Up to about 30-35 mph, they didn't move at all. Above that, they indicated that some air was going into the engine compartment.

But that may have just been turbulence. I parked and turned the A/C on to turn the radiator fan on. Engine was well warmed up (170F oil temp) but I could feel no heat coming from the rear of the hood. On inspection, I found the gap between the hood and the engine compartment is very small.

My conclusion is that removing the seal doesn't accomplish much, if anything. Off to put the seal back on.
Edit: the fasteners for the seal are not evenly spaced, so it's all but impossible to install it wrong.

So it stands to reason that if we opened that gap up somehow we would be making matters worse as far as airflow is concerned? Thanks for actually testing it, too much of this is theory.

Looks like it. :(

I'm rather surprised the the radiator fans wouldn't push at least a little bit of air out when parked. Where is the air going?

It would be interesting to see a similar test run with the undertray vented. But I'm not gonna hang my head out the door and look under the car while going 60 mph. :)

Has anyone looking into a very high static pressure fan setup yet? I know the GTM fans are better but does anyone have static pressure data on stock vs gtm?

Man, I just loathe to give GTM any more of my money.