Thread: Lowest air pressure/highest air velocity part of the hood?

Could always do the super cheap way install a backwards STi hood scoop.

Marine Black ABS Plastic Louvered Vent for Boat Caravan RV ? Five Oceans | eBay

picked up one of these, too cheap to not give it a go. not a large area but should be of some benefit.

It's pretty small but maybe another one of these above or to the side of the existing one, or even 4 in a quad 2x2 fashion next to each other for lots of venting. Not sure if I want to cut up my hood just yet though...

Got my new thermal camera in, the model is the Flir C2 if anyone is interested. I took a pic of the hood of my B15 Sentra last night when I got home. I have a VERY short commute, all of about 5 minutes, so I sat in the driveway keeping the engine revving between 1k and 2.5k. At roughly 15 minutes, here is what the hood looked like:



I took two earlier shots, and was watching those hot spots on the sides grow. Obviously under harder driving conditions there would have been more heat over time, but I could only sit in the driveway so long last night. It's raining here today, so not a good day for thermal pics of the hood, but if I take a drive at lunch later this week and it's dry I will try to get a pic with more runtime on the engine.

I was initially surprised by where the heat was showing on the hood, a hot spot over the pulleys and the transmission didn't make sense, but then I realized that while sitting there the fans on the radiator were probably running, and all that air was getting pushed to the sides and out the bottom. This last pic was finally starting to show signs of heat in the center, this obviously would have kept growing over time as everything else warmed up.

So, what this tells me is that the vents along the sides of the hood are going to be doing the most good at venting heat, it is obviously getting trapped there. It isn't clear to me at this point if additional venting in the center (like the GT-R pic) would be as helpful, though those vents are more likely there for downforce rather than venting, but of course I'm sure that they do help there as well.

Like GTi-R vent placement...

Thanks for that post jimbo. Would love to see one of your B13 immediately after a race.

@jimbo_se-r ; A car sitting still, does not exhibit the true airflow effects within the engine bay and over the vehicle. Once the vehicle is in motion, those stagnation temps may or may not be the same. Airflow occurs within the engine bay as well.

What does the temperature profile look like immediately after driving then stopping?? This may or may not paint a different picture.

Well, like I said, I have a very short commute, so all I saw when I immediately hopped out of the car to take a pic was the two warm spots there forming. The pic looked fairy similar, it just wasn't as hot yet. I totally understand what you mean about the airflow in motion, and totally agree.

I just got back from lunch, and snapped three more pics, as follows:




The above pic was from a drive down the highway, drive time was about 12 minutes, 10 of which were on the highway. I intentionally used lower gears whenever possible to keep the revs up, anywhere from 3k-5k. Outside temp was about 75 degrees.




This one kinda surprised me. After eating lunch (about 15 minutes later), I was expecting the hood temp to have evened out, and it was sitting in the sun (black car, Texas heat, loads of fun). But I was surprised to see the temp range had risen quite a bit (up to 158F from 132F on the high end), and you can clearly see the radiator, header, and valve cover areas are now showing the most heat. I was just doing some googling, and this phenomena is called Heat Soak.




Another surprise pic. Drove back to the office, I don't think the revs were quite as high on the way back, but still 3k-4k range in lower gears. Both the restaurant and my office are only about a minute off the interstate, and I tried to keep the revs high to keep things hot. But this ended up being the coolest of the pics, with the high temp now only 112F. I'm guessing that the radiator fans kicked in a lot sooner than the earlier drive, and so were able to cool things down better?