I was thinking about this as I drove home today.

October 31st in Tampa, Florida at 12:30 PM
Ambient temps: Mid 80s F
Water temps: 88-94C
Air Temps: 50-60C

My car gets ridiculously hot under the hood. I got home from my 40 minute drive with the AC on high ("boosting" only once the entire time) and popped the hood, and the heat just poured out from under the hood. My large K&N filter was hot to the touch as was most everything else. I will be having some body work done on the car in the next month or so and have been debating on whether or not to get a vented hood. The only one that I believe is signicantly functional and yet does not ruin the lines of the car is the Knightsports hood.

With that in mind, I was thinking... Would it be worthwile or even a good idea to create some kind of "tunnel" for the air to pass through starting with the bumper opening and ending with the large vents in the Knightsport's (or any other for that matter) hood? To clarify, air would go through (in my case) the FMIC and be forced to go through the radiator (and AC condenser) and then would be guided upward with maybe an aluminum sheet to the large center vents in the hood. This would be done around all sides creating a tunnel so that the air would pass through all of the important heat-exchanging devices and then be forced out of the hood rather than trapped and possibly vented (if one had a vented hood without said "tunnel"). I'm not sure whether the actual motor relies on any airflow for cooling. It would seem to me that any air that happens to hit it would already be superheated, so it would probably do little or no good anyways.

So, what do you think? It seems like a good idea to me. Of course, it would require a bit of time for fitment and fabrication, but I'm always looking for ways to make the car to perform a bit better.

For those of you who may be unfamiliar with the Knightsport's hood...

 

There needs to be some airflow through the engine bay, otherwise components like the turbo and exhaust manifold will continue to heat the underhood air even more. Any heating of the air by the radiator/IC is minor compared to the heat radiated from the engine. If there was any airflow from the rad/IC being "trapped", both of those components wouldn't be functioning properly. You could possibly increase the efficiency of the radiator/IC by specifically directing airflow afterward, but at the expense of underhood components.

 

I've seen the Apexi RX-7 that has this air tunnel done to it. But they had a v-mount setup where the air was forced through either the radiator or the intercooler. The air through the radiator remained in the engine bay. The air through the intercooler exited via the vented hood.

It seems as though an air tunnel would only be necessary for track racing. A regular vented hood should be sufficient for street driving.

Would a heat shield around the exhaust manifold solve that problem?

 

To a certain extent, but you would still have major heat radiating off the engine block that would continue to heat up the underhood air if there was no circulation.

Apexi was probably trying to increase the airflow/efficiency of the IC by redirecting the airflow afterward. Creating a major low pressure zone after the IC helps "pull" the air through.

 

Makes sense.

I think it's also important to consider that the engine bay is constantly under pressure while driving so any sort of venting would be a release of that pressure. Thus the air would most certainly vent regardless of whether it was tunneled or not.

I'm sure there are posts out there of temp reading differences and general engine bay heat relief after the installation of a vented hood. I'd say install it and if the differences don't meet your standards then look into the air tunnel idea further.

 

cruising with 50-60C IAT sounds very high for your set-up, even off stock sensor.

 

Well, I wasn't exactly "cruising." This was stop and go driving around town during the heat of the day. The IATs will stay in the 30s or low 40s while actually "cruising." When I pop my hood after recording these 60+ IATs, the K&N is hot to the touch, so I think a big part of my problem is that I'm just sucking hot engine bay air into the filter.

 

Some carefully constructed radiator/IC ducting can go a long way.

 

the FMIC with fans on likely cools your hot intake system, but low charge air flow in traffic allows reheating aft IC. could insulate some of the piping, and plug the tb heater.

http://www.autospeed.com/cms/article.html?&A=0401

 

Even the Knightsports hood doesn't really flow well with the lines of the FD. Much better than any of the other hoods though.

 

A fan mod will go a long way toward reducing under hood temps. With the fans running, coolant temps will remain close to 180 degrees. With coolant temps lower, engine temps will be lower, and under hood temps will be lower. In addition, having the fans running will create air movement under the hood, pushing stagnant hot air out ..... mostly under the car.

If I am going to be in any kind of "stop and go" traffic for more than a couple of minutes, I always run the fans.

 

Stock fans are set to run on high all of the time. 2 additional 10" fans are positioned blowing air through the re-positioned AC Condenser and Radiator.