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Cooling System Efficiency

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wishihadatalon

20+ Year Contributor
2,615
72
Aug 18, 2002
Grand Rapids, Michigan
I have some questions that I am hoping that there are people who have done some in depth cooling system work and are willing to share.

First I would like to say that given all of the things working against me, this car cruises at acceptable temps (~186 +/- 3 degrees) on the highway without radiator fans and around town (191 +/- 2 degrees) with occasional fan use. Additionally, at a stop light, my single 14" puller fan can reduce temperatures by ~5 degrees during the course of a normal stop light.

With that said, the back story for the car is as follows. Over the last year, I have upgraded the turbo and intercooler system on the car from a Swaintech coated FP manifold with a 16g and stock side mount intercooler, to an uncoated Punishment Racing t3 manifold, HX40 turbo, front mount built by yours truly (dimensions 24x10.5x3.5") and a 1g koyo radiator. The car is a 95 talon and I'm a purist so it still has a 95 front bumper and factory fog lights. The front mount removed all factory ducting and fills the entire opening for air flow to the radiator. Obviously before I never had issues with cooling and I would say that the car does fine now, but I think there is always room for improvement.

So, I know I can improve some things with simple thermal management items like ceramic coating of hot parts, turbo blanket, etc. and also by adding ducting (which I plan to do this winter), but I would like to lessen the load on my radiator fan and increase the efficiency of the system. My question to people with experience is all about post radiator engine bay pressure management. The factory way of evacuating air pressure from the engine bay is out the bottom of the car, correct? Is this way of evacuating air from the engine bay sufficient? Is there room for improvement? If so, is that method some sort of under tray with a lip at the front? I prefer the clean and simple look of a factory hood, so utilizing some sort of hood vent would not be ideal. I don't road course the car, nor do I anticipate doing so, and the amount of improvement I am looking for should (in my opinion) be achievable without a hood vent.

Any insight, recommendations, or comments are appreciated.

Thanks,

TJ
 
You're definitely on the right path. You are correct, the bay is evacuated under the car. That provides some other interesting benefits, but that is another discussion. Ductwork will make the single biggest difference. Basically, you want to encourage the biggest practical pressure differentials across the two heat exchangers to get as much of the cooling fluid mass passing through them as possible. Try to envision a sealed tunnel from the bumper through past the sub-frame, that's what you are after.

Even on >90*F days, getting off the freeway after some pulls and stuck in traffic on the ramp waiting for a light I've yet to have my coolant temps break 170F. That is probably approaching too cool for a street application, but I'm hoping it will prove helpful in the 1/2 mile and longer events.
 
A properly setup external oil cooler would also help keep the coolant a little cooler also.
 
You're definitely on the right path. You are correct, the bay is evacuated under the car. That provides some other interesting benefits, but that is another discussion. Ductwork will make the single biggest difference. Basically, you want to encourage the biggest practical pressure differentials across the two heat exchangers to get as much of the cooling fluid mass passing through them as possible. Try to envision a sealed tunnel from the bumper through past the sub-frame, that's what you are after.

Even on >90*F days, getting off the freeway after some pulls and stuck in traffic on the ramp waiting for a light I've yet to have my coolant temps break 170F. That is probably approaching too cool for a street application, but I'm hoping it will prove helpful in the 1/2 mile and longer events.

You're response is exactly inline with what I have learned and thought. I certainly understood the pressure differentials and I figured the best possible way to make the radiator work well with the intercooler is to find a way to make the engine bay as low pressure as possible. I like the idea of mid 180s all of the time while the car is moving. If the fans only work while stopped, I consider that a win. Did you make some sort of under tray? Anything you're interested in sharing? I assume you have designed/built your car for competition, so I would understand if you didn't want to.

The way I was thinking about doing the tray was sealing the bottom to the sides (like you mentioned) and then doing some sort of 5ish degree flare downward at the back of the bay.

Also, I think an oil cooler is simply a smart idea and one that should be practiced. With that said, I have a 90 ofh on the car and I have the external cooler ports blocked off. I usually change the oil early and haven't seen any negative effects (occasional use toy car), but it is something that I am looking at for this winter as an upgrade.

Thanks guys.
 
I also have a 90 OFH, cooler deleted at the moment. May add it back in after more testing of a couple hypotheses or if I find I can't keep oil temps in check through other means as she gets some proper track time and start turning the boost up further.

Belly pan is only in the draft stage at the moment. I'm redesigning my bumper cover/airdam and skirts, as well as how my hood seals at the front and where my DP/dump tubes come through. The old setup was not super sophisticated but it worked very well. You can sort of see in my avatar pic.

This last few months I've been working 60-70 hours on average, which has been awesome for the car fund but no bueno for actual tweaking.
 
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Have you checked out the Grey Forrest Mod hood vents?
 

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The OP said no hood vents but I have to say seeing as the evo 1 came out in 92 with hood vents, is it safe to say that the clean look is not practical enough to reduce engine temps? I'm all about clean looks but if Mitsubishi added a vent 2 years after the 1g doesn't that mean anything? I'm going to look at a evo style hood vent for my 1g as I can see how functional it is over the form it looks.
 
You can add vents, but you're adding to the problem of underhood pressures. You're now adding more pressure and will have to get more creative getting that air out. It can be done, just adds to the equation.

Btw the Evo x has a functional style air scoop. Also has an under tray to help evac.
 
You can add vents, but you're adding to the problem of underhood pressures. You're now adding more pressure and will have to get more creative getting that air out. It can be done, just adds to the equation.

Btw the Evo x has a functional style air scoop. Also has an under tray to help evac.

What would be the ideal to lower the engine bay temps?
 
You can add vents, but you're adding to the problem of underhood pressures. You're now adding more pressure and will have to get more creative getting that air out. It can be done, just adds to the equation.

Btw the Evo x has a functional style air scoop. Also has an under tray to help evac.

Hood vents have to be placed properly to exhaust air pressure from under the hood instead of introducing it, but they most certainly do. Combine them with some sort of duck bill at the leading edge of the vent and they work extremely well. Again, I know I could get the results I want with a hood vent but it doesn't fit into the idea I have for the car.[DOUBLEPOST=1410103305][/DOUBLEPOST]
I also have a 90 OFH, cooler deleted at the moment. May add it back in after more testing of a couple hypotheses or if I find I can't keep oil temps in check through other means as she gets some proper track time and start turning the boost up further.

Belly pan is only in the draft stage at the moment. I'm redesigning my bumper cover/airdam and skirts, as well as how my hood seals at the front and where my DP/dump tubes come through. The old setup was not super sophisticated but it worked very well. You can sort of see in my avatar pic.

This last few months I've been working 60-70 hours on average, which has been awesome for the car fund but no bueno for actual tweaking.

What's the old saying, "when you have time, you don't have money and when you have money, you don't have time"? :(
 
Good topic. And basically overlooked. Our IC engines are ~35% efficient (from fuel energy). Soooo.... 65% of our fuel energy is waste-heat. Only way around that is running a ceramic engine at extreme temperatures (efficency = delta T... steel & iron melt at high dT). What that means is... when we boost HP by 100% we increase the heat load by the same amount. Getting rid of the heat is important. Preventing heat from entering is even better. Steps include:

1. cool air intake. cooler=better. Box off the air filter from engine bay. Supply cold air with duct.
2. oil cooler. Turbo = oil cooker.
3. Wrap turbo & exhuast manifold & sheild turbo. Heat & pressure into a turbo = HP. Keep it for the turbo... not your radiator.
4. wrap & sheild the cross-over water pipe behind the turbo (it is only inches away... soaking radiation energy from that turbo into your coolant.
5. shield exhaust & everything. Preventing heat from entering engine is better than soaking it up then trying to expel with radiator.
6. Intake manifold gasket? not sure how much benefit... but keeping heat out is good.
7. Believe it or not. All radiator fins are not created equal. Tear apart an OEM radiator... are the fins solid or luevered?
8. Water is a better coolant than Glycol. Water with surfactant is the best coolant.
9. Ceramic coated components. Careful... don't want that coating to flake & get into turbine.
10. Polishing piston faces, valve faces, & chamber? Will this reflect heat? I dunno. But mine are 1000 grit shiney. Dull surfaces (more area) absorb more radiation.

I know it sounds wrong... but... arbitrarily adding hood vents may or may-not help. OEMs spend millions on under-hood CFD analyses in-order to provide cooling. Knowing where positive & negative pressure regions are... and planning airflow paths is not simple. So... maybe your hood vents are cooling the engine... but do they push air under the vehicle? Windshields are high pressure regions. Generally, (drivers of) high speed vehicles like low pressure under the vehicle. Again... I do not know the right design answer... Look at the low pressure region of an air-foil and guess where that spot is on our hood. Better yet manometer & pitot tubes or CFD if you got Physics.

Air enters our engine-bay low in front. Does it stay low & exit? or does it go up... over... & cool. Probably stays low and exits. My guess is a covered belly... with NACA ducts supplying air to critical areas... with planned exit paths is what a pro would set up.

BTW... #3 above may reduce thermal fatigue on exhaust manifolds/tube-headers. Rapid heating & rapid cool thermal cycling is never easy on anything. Wrapping will reduce thermal gradients.
 
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Very good info! It's making me think twice about a vented hood as there's more involved than just a "vent to remove air"
 
I may be thinking too shallow about this, but what about a sort of lip but farther in that directs a small amount of air up across the front of the motor?
Pretty much it would be mounted behind the front bumper lip, only hang about 1/2" to 1", and be angled just slightly. This would direct more air up into the engine bay. It could even be attached to the radiator core support. I feel too much of an angle though and you would create upforce across the front at high speeds.
 
a sort of lip but farther in that directs a small amount of air up across the front of the motor?
Pretty much it would be mounted behind the..... This would direct more air up into the engine bay. ...across the front at high speeds.

Might be the best thing ever.

Generally we think of directing air with high pressure (lips, fins, etc). Air flows from high pressure to low pressure... it needs both.

Some things I thought would work great in the wind tunnel didn't work out so well. Others worked great. Sometimes measuring or analyzing the changes is the biggest challenge. Measuring brake rotor temperatures on a full vehicle in wind tunnel with a rotating wheel was interesting. Three pyrometers, sliding thermocouple, and inner/outer pad imbedded thermocouples(all on one rotor) each device provided a different temperature. What would you do next? Tunnel time is not cheap and the clock ticks. Stakes are lower on your own time but wrong decisions are a waste of time and effort.

Bolting parts on a car are guaranteed to do one thing... add weight.

look at new Corvettes, Evos, Other DSMers... not at a bolt, hood, or fin.... look at the system. How does the system work, or does it work? A few engineering classes and alot of experience goes along way. search for vehicle CFD pics on the web. Learn how to use a pitot tube & yarn... don't melt your GoPro.
 
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So I am of the opinion that further help to evacuate the engine bay should help my situation quite a bit. I base that assumption from coolant temp measurements on the highway with and without my radiator fan on. I can actually see an increase in temperature if I run my radiator fan on the highway. This to me says that my engine bay pressure is too high and thus killing the pressure drop across the core of my radiator. This also tells me that my coolant system could potentially handle even more load and still be successful. From that, I would say that introducing more air to my engine bay to cool parts would be a poor choice to lower temps. I'd prefer to use my engine as a liquid cooled engine vs. trying to make it an air cooled engine.

Again those are assumptions at this point, but I think they are pretty fair.
 
I may be thinking too shallow about this, but what about a sort of lip but farther in that directs a small amount of air up across the front of the motor?
Pretty much it would be mounted behind the front bumper lip, only hang about 1/2" to 1", and be angled just slightly. This would direct more air up into the engine bay. It could even be attached to the radiator core support. I feel too much of an angle though and you would create upforce across the front at high speeds.

This is completely counterproductive to the system as it will increase pressure behind the radiator and thus reduce the pressure differential across the radiator.
 
Its a little expensive but look into evans waterless coolant. Its also helps reduce temps and its a simple fluid swap! Ive just got some but not put it in yet however my friends are using this and have seen a nice result! Its used in a few leman cars and moslers. Check them out. Will help a little more aswell with the other items
 
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