Welcome to the SR20 Community Forum - The Dash.
SR20 forum logo

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

+ Reply To Thread
Posts: 11-20 of 28
2016-03-21 21:12:17
Last edited by jimbo_se-r on 2016-03-22 at 14-54-19. Reason: Double Post
2016-03-21 22:58:00
The lip needs to be raised more. It creates a venturi and draws the air thru.
2016-03-21 23:39:18
@jimbo_se-r , The lip needs to be, at a minimum, as tall as the height of the highest slat. And yes it does make a difference. It's all about manipulating airflow and direction.

Below is a very illustrative and accurate explanation of the topic in discussion


Also, I want to stress; location of vent is JUST as important as venting the hot air itself. About 95% of the aftermarket hoods in the 240sx community for example, place the vent too far rearward of the radiator and do not truly exhaust the hot air through and exiting the RADIATOR. The confusion lies in the distinction between exhaust from the radiator vs exhaust from the engine bay, with the prior being on the order of magnitudes more important than stagnant engine bay temps (which are exhausted through the cowl area). The idea is to get the high pressure/high flow stream through the radiator, redirected up and out the engine bay. This not only drops the pressure differential over/through the radiator (which promotes flow through the radiator and inturn, allows more air mass to pull heat from the fluid with heat transfer), but also relieves engine bay pressure which equates to less lift and more high speed stability. Engine bay pressure build up is also a counterpart of lift generated on the front end.
Last edited by Boostlee on 2016-03-21 at 23-40-45.
2016-03-21 23:45:48
Pulsar gtir vents? Nissan OEM.
2016-03-21 23:51:26
Sorry for the double post above, first one froze and didn't appear to have posted when I made the 2nd post.
2016-03-22 00:01:21
Originally Posted by SE-RMonkey
Pulsar gtir vents? Nissan OEM.

The side vents, yes. The entirety of the vent (including the first element) actually is turned up (forgot the term), so a diffuser is not needed at the leading edge. The first element/slat/fin/whatever takes care of redirecting the airflow (and subsequently, so do the remaining elements). However, they are much too narrow to be of any significant use apart from a small heat exchanger or similar heat source.
2016-03-22 00:38:51
In for Dildo-based rallycross starring Lee in his B13. That, I definitively must view.
2016-03-23 02:41:10
Good to know about the turnups. Not so good to know about Kyle's fantasies. Thanks guys.
2016-03-23 19:20:47
Originally Posted by wildmane
Good to know about the turnups. Not so good to know about Kyle's fantasies. Thanks guys.

I did not mention the dildo's flying into your radiator but once I read that, that sparked an undying desire to view such a marvel.
2016-03-24 15:11:40
Looking at the graphic that @SE-RMonkey posted above, while not a B13, the lines aren't too different from our cars, and can serve as a decent example. I did some Googling and didn't find anything specific to our cars. I'm actually shopping around for a thermal camera at the moment, so I may be able to provide some pics down the road.

I did, however, find where he lifted that graphic from, so I'll give credit since it is also a good read: Car Aerodynamics Basics, How-To & Design Tips ~ FREE!

The outline of the B13 is similar to the above image, the main difference being the bumper in front that will serve to divert airflow a bit. The area above the bumper has a slight slope, further back on top, so that will have air moving up over the hood just a bit more than what that graphic shows.

My original thoughts on dissipating underhood heat were to have vents further back, more over the valve cover area itself, but in reading through the info I've collected this would have been too far back to be effective. It would have helped, but not as much as something more forward, and what I was thinking of wouldn't have impacted the aerodynamics much. Increasing downforce in the front would be a bonus, so why not do both?

I'm seriously looking at doing something similar to what the GT-R has in the photo above. If you go to the link I referenced, there is a great video showing this car up close, especially the hood area, and there is also a segment where the hood is off and you can see the underneath side of the hood, which for me is very useful. The video is in Section 10, Rear Wing. At 1:14 is a great shot of the hood vents, you can see that the middle vents are slightly taller than the row along the side closer to the camera, but it seems that the far side may be the same height as the middle section? Maybe it is an optical illusion, or else some intentional design to have more downforce on that side? In looking at the view under the hood (starting at 1:25) these don't appear to be adjustable in any way. I'm estimating that the height of the shorter vents is about 1", and the taller ones about 1.75", or thereabouts.

My original thought on hood vents was something similar to the S2000 project that @Boostlee posted (I had come across that one myself a while back when thinking about this), but I really like how the GR-R vents have sides as well, so I'm thinking on how I can accomplish that. My current thought is that I will cut out a rectangular shaped section of the hood (folding over about 1/2" of metal along each edge to avoid having a sharp edge, but more importantly to retain rigidity from the lost bracing underneath), and to fabricate a separate vented section that would mount from underneath. How exactly that separate section would be constructed is still up in the air...
Last edited by jimbo_se-r on 2016-03-24 at 15-24-05.
+ Reply To Thread
  • [Type to search users.]
  • Quick Reply
    Thread Information
    There are currently ? users browsing this thread. (? members & ? guests)

    Back to top