So a big issue with a turbo charged car is the amount of heat generated by the charged air flow. Our cars have two vents that allow "exhaust" air, that cools the intercooler, to be sucked into the atmosphere there by cooling the engine bay. As many of you have noticed they are very restrictive. A very easy and quick way to fix this problem is by taking out the two plastic vents. To do this you will need a 10mm socket. Loosen and remove the four nuts on each vent with your socket. There is another small plastic pin that you must compress, use your fingers, and push out. Once you have the vents out, look on the back side of them. There you will notice that the vents are actually made of two pieces. You can remove the bottom piece by simple pulling the plastic clip away from the vent. Insert the clip back after removing the thin piece of metal and then re-install the vents. Note: I repainted them using two coats of high heat paint since I am guessing the metal was there for that reason. I will post pics tomorrow after class.

 

in for pics to see what you talkin bout willis

 

+1 for pics

 

I think he's talking about the 2 hood vents in front of the scoop. He's under the impression that the air goes into the front of the car and then up and back out through those vents. While this is true, I think it's a very small portion of it that actually goes that way. At low speeds, opening up those vents might get a tiny bit more cooling. At high speed, I doubt it'll do much at all, especially since our intercooler is at the bottom half of the radiator.

 

I don't know how much this would help with airflow...but I do know that those vents do a proper job of extracting heat from the engine bay if left as-is. Multiple times during past winters, I've noticed that the snow and ice around the vents melt quite quickly in the direction that the vent openings are pointing (up towards the windshield).

I wouldn't say that the vents "suck" hot air out from the engine bay area, but rather, I think it provides an opening for hot air to rise out of the engine bay. It could be different at high speeds, where high and low pressure areas come into factor, but I do not know.

Still, in for pics.

 

More than likely the speed of the air going over the hood helps to extract heat. The faster moving air over the hood creates a low pressure area vs the high pressure area under the hood, creating a lift or draw of the air under the hood out through the vents. This works at moderate to high speeds. Around town driving it won't have much effect, other than venting some air.

 

Removing the slotted vents will actually increase heat under the engine bay. Here's why: When air travels through the vents it gets compressed and speeds up. This creates a small vacuum that sucks more air through the vent. This principle of aerodynamics is the reason the Evo, and the RA to lesser extent, uses a diffuser on the rear of the car. In the case of the diffuser the accelerated air creates downforce, in the engine bay it assists with heat extraction. In fact, judging by their placement, the vents main goal is to remove excess heat primarily from the radiator. So, unless you are overheating, modifying these vents will have little to no effect on engine performance.

BTW, the center scoop is designed to funnel air onto the turbo to assist in cooling, it would prove more beneficial to modify that opening than the ones in the front.

 

extract or not .. i believe the front vent are made to extract heat from the radiator, not the intercooler...
and even if u can get a "cooler" intercooler, does it actually make ur actual turbo cooler?

I believe the only solution to cool down the engine bay are the side vent on the Evo 10 (or just run without a hood...)

 

The whole point of the front vents is to remove the air flowing past the intercooler and radiator AWAY from the rest of the engine bay. The air passing over both of those is hot and by removing it the engine bay become cooler. By the way, it is a generally accepted rule that for every 30 degree that the engine bay gets cooler you can add about 2HP. The side vents on the Evo help cool the brakes, A cooler intercooler cause the air going into your intake manifold to become more dense therefor increasing power.

 

Results:

I did a fairly simple test to see how much of a difference was made by doing this. As it turns out it makes a fairly significant difference. I measured the temperatures of the vents after driving for an hour ( one hour with no plates, one hour with plates. I took a brake in between as to let the bay cooler to ambient temperatures.). The general rule of heat transfer allows me to do this because the vents are undergoing convection from the hot air passing over them. Using the standard specific heat of most plastics I determined that there is about 9-11 KJ difference between both situations. So on the low end that means there is about 2 KJ/KG difference in cabin air. Which correlates to 3 degrees Celsius difference in temperature (or 7 degrees Fahrenheit). This was a very simple test with LOTS of factors left out like radiance (which is probably negligible), flow velocity, and turbulence, all of which would mean there is actually a GREATER difference in temperature. lol so much for going to class :P

EDIT: I would estimate a 10-15 degree F difference in temperature.

 

If hood vents are so important to cooling an engine, how come you only see them on street cars? The only hood openings you see on race cars are the ones designed to shovel cold air INTO the engine. This is the important temperature! Concentrate on bringing the intake charge down as low as possible, and you will make far more hp than any slot in the hood ever will. Given that a good aftermarket FMIC can get the intake temp down to ambient, I'd say that is all you ever need unless you're making significant mods.

 

here are the pics.

 

I have to say there are some flaws to your experiment. First, we aren't looking the temp change at the vent, we are looking for temp change in the engine bay. All your experiment proved is that the vent is cooler if you take off the blades. This could be caused by less overall airflow travelling through the vent, and thus a cooler temperature. Second, differences in the ambient temp, wind speed, average vehicle speed, and exposure to sunlight can skew your results by a wide margin. Third, you didn't specify whether you are basing your results on delta temperatures from the beginning of the run to the end of the run, or whether you are just comparing overall final temperatures.

I will say that a temperature of 15 degrees F is not a great amount considering engine bay temps regularly exceed 500 degrees F, and the measurement location is quite a distance from the intake manifold, turbo, and exhaust.

 

As I recall the Ford GT-40 has a similar vent that is much larger than ours. And it won a ton of awards. street cars aren't the only ones with vents. Look around and you will notice them on a ton of stuff. And a lot of racers vent to the bottom as well.

 

That is the part where convection comes intop play. And NO the vents are not cooler when you take off the plates they are in fact hotter. (which means more hot air is leaving the engine bay. "(differences in the ambient temp, wind speed, and exposure to sunlight can skew your results by a wide margin)" all of these would me minimal to the convection HEATING effect of the hot air passing over the vents. "( All your experiment proved is that the vent is cooler if you take off the blades.)" you obviously don't understand how thermal conduction, convection, and radiance works. And yes it is the difference between the two final results. Which means there is an ADDITIONAL 15 degree F cooling effect to the bay. Also, i drove around on the Lubbock "Loop" which has no traffic, with a constant speed of 60mph. I averaged 59 with the blades and 56 without.