280Z Hood Vent Placement?

[Sandy455]

I'm running a 240Z L24 with a solid hood but having the head ported/polished/rebuilt to run at higher RPM's during So Cal track days which will mean even more heat under the hood so I purchased a pair of bitchin' Skillard.com louvered hood vents intended to replace the factory 280Z hood vents.  I'm figuring I'll just base the placement on the left vent over the rear SU carb (and match the right side vent) when my body shop cuts the holes in the hood next week.  But does anyone have the exact dimensions from the edges of the hood where the factory vent holes are set?  Thanks.

[Miles]

Or you could use a 280Z hood that has the cut outs. Plus the holes in the 280Z hood are recessed for the louvers.

[Sandy455]

Yes.  Also a good idea. But the vent base plate is maybe 1/16" thick and the mounting screws are built in so the top is smooth.  Plus, I need the louvers as high up as possible because it's the cooler air rushing over the hood that sucks the hot air out from under the hood at speed. (Some law of physics I can't name.)

Edited August 7, 2016 by Sandy455

[Oblithian]

I was under the impression the 260 and 280 have longer hoods. But having the vents near the windshield will be best in terms of reducing the pressure that builds up by the hood latch. So yes if reducing engine bay air temperature is your goal, that should help.

..Though there may be some unintended effects on drag and downforce.

Out of curiosity, are you having the head modified for injection while you are at it?

Edited August 16, 2016 by Oblithian

[Pillar]

I am not sure where the topic was exactly (some searching will turn it up I'm sure, and I will take a look to see if I can find it) but I recall that it was discovered that having the vents placed further forward on the hood was best for relieving the built up air pressure and increasing cooling.  This is due to the fact that there is actually a high pressure area right at the cowl where air piles up in front of the windshield.  This high pressure area actually minimizes the amount of air being "sucked" out of the vents.  I dont remember anyone actually posting a specific location with measurements, but it seemed the general consensus was that the best placement was about 1 foot further forward than where the stock vents actually were.   

[Pillar]

http://forums.hybridz.org/topic/94550-fender-vents-general-aero-questions/

 

This is the thread I was thinking of.  It starts out as a discussion about splitters, but moves on to cover venting built up pressure under the hood through the fenders and hood/cowl area.  On page 2 it gets into the possibility of venting through the cowl, but was stated that it is a high pressure area (the idea is to vent to a low pressure area to maximize airflow) and thus would not be the best place to vent the engine bay. the post at the top of page 3 also has photos of a Z with vents (not stock) placed further forward on the hood (in keeping with the idea that it is a better position for airflow).  

 

http://forums.hybridz.org/topic/56546-hood-vents-ideas/

 

This thread also goes into some detail about the high pressure buildup in front of the windshield.  Worth a read.

Edited August 16, 2016 by Pillar

[Miles]

http://www.ztrix.com/hoods/hood-with-cooling-vents.html

[260DET]

http://www.ztrix.com/hoods/hood-with-cooling-vents.html

 

Oh yes, they will work much better than the OE type ones, plus they are located well.

[Oblithian]

Right, A low pressure would be much better for a draw from on top of the hood. I was thinking of draw from under the car, though it would likely be warmer so that is not the best concept. Even though flow would be higher, it would likely be moot because of how much higher vacuum pressure is than air.