Belly pan + Cooing (Mental exercise because why not)

[Sideways]

This thread is just a mental exercise, just to brain storm, have some fun, and see what kind of ideas other people come up with.

We all (well, most of us) seem to love the idea of a belly pan- They seem to be the mythical holy grail of aerodynamic goodies for quite a few of us.  While pondering on the idea, a question/concern crossed my mind.  Cooling.  If you were to completely seal the bottom of the car to make it perfectly flat, what would you do to deal with the air going into the engine bay?  Obviously its beneficial to limit how much goes in in the first place, but even if you limit it, what goes in still needs to spill out somewhere.  Will enough be able to travel down behind the engine/out through the transmission tunnel (and maybe out a vent/opening you leave at the rear above the belly pan, or diffuser if you go that exotic with it)?  Would you go with hood vents?  Would ducting the inspection lids allow enough air to escape, or would you still pile up too much air and run into aerodynamic/cooling issues?

Would love to hear ideas/input from everyone.

Edited March 10, 2014 by Sideways

[JMortensen]

There is a guy who did his own on a Miata and he put NACA ducts in it for the trans and the diff, and then left a space above the diffuser to let that air out. Here is his thread: http://clubroadster.net/vb_forum/89-roadster-projects/44470-my-na-becomes-track-car-build-thread.html

[johnc]

The cars had a front pan from under the radiator to the front cross member from the factory.  That actually helps cooling.

 

For most production based front engine/RWD cars that have a sealed under body, radiator and under hood air is exhausted through the hood and the back side of the front fender wells.  Transmission and diff coolers are mounted remotely with ducting from the sides of the car and exits above the rear diffuser as Jon mentioned above.  The idea is to not disrupt air flow under the car so diffusers can work. 

 

I've gone that route with a customer's E36 BMW and it worked vary well at speed.  Its not as effective at low speed and at idle so you have to minimize time spent not moving.

[260DET]

Depending on wether cooling air is needed for the gearbox and diff, aero wise the less air that goes under the car the better. Both for drag and vertical force reasons. The inspection lid openings are nowhere big enough to vent sufficient air, to get an idea of the size required have a look at those factory cars which vent the bonnet just behind the radiator position. As for diffusers, that Z I posted a video of at Phillip Island has front and rear diffusers, it's lap times indicate that the aero on that car works very well.

[roger280zx]

There was a viper acr a few years back in Hot Rod mag that had an aluminum under tray, everything was sealed except the rear diff.  There was a naca duct that opened just before the diff and expanded out just beyond its housing and then vented behind it.  I thought it was quite the novel way to cool the diff.

[Sideways]

There was a viper acr a few years back in Hot Rod mag that had an aluminum under tray, everything was sealed except the rear diff.  There was a naca duct that opened just before the diff and expanded out just beyond its housing and then vented behind it.  I thought it was quite the novel way to cool the diff.

Happen to look like this?

 

 

These are the factory pans on vipers. 

[260DET]

Very worth while doing a search here too, lots of aero orientated mods and tricks have been done and discussed, including modding the grille area to better control and direct airflow.

 

Love the NACA duct idea ^, much better than relying on random airflow. That demonstrates the basic concept when doing aero mods, to control and direct airflow for specific purposes 

[mmendes]

First off Id tip the radiator as far forward as it would go so I have as much room to vent out the top of the hood. Two fog light sized brake duct holes. I guess I wont go into the aero portion since were focused on cooling. Ive always thought running a short wide radiator towards the bottom of the opening would allow more space for a trans/oil/inter cooler in what is left of the opening.

 

 

If you look at the pic you can see what this team has appropriated the frontal area to each cooling device. You can also see what are either brake ducts or one is for that hose feeding the carb area fresh air. I guess I would combine this radiator placement with ducting like you see on that BMW.

 

check out this tread for a good examples and ideas of ducting. Amazing aero work being done on this car once it got serious

 http://www.dsmtuners.com/forums/custom-fabrication/386716-my-ducted-radiator-setup-road-racing.html

Edited March 25, 2014 by mmendes

[Tony D]

Actually, the factory option parts covered from the G-Nose (which sealed on the bottom side to the radiator crossmember, to in back, halfway down the transmission. It was an FRP underpan, and was open on the exhaust side so any air let into the engine bay was biased to exit over the top of the tranny and on to the exhaust-side of the car.

[roger280zx]

Yes, that looks like the pan.  But this cars pan was modified with a naca duct iirc.

[Sideways]

So if one was to run a slightly blocked off grill as many members are (not blocked off enough to cause over heating issues on its own), and run a relatively well sealing belly pan- Is it reasonable to assume that if A) The "exit" area for the engine bay is the same area size as the inlet, and , where this air exits is lower pressure than the inlet- Youd be able to move enough air through the radiator to avoid over heating?

[260DET]

Yes Sideways, absolutely. Once the idea that 'what goes in has to come out' is understood the rest is easy. High pressure inlet, low pressure exit. Of course the execution has to work accordingly.

[grayson260z]

Kinda unrelated but my cousin said back whenever he used to race his 240z he got the idea to take the piece from under the radiaror out and race like that to see if it helped any with aerodynamics. Instead of doing that he said it started lifting the front of the car whenever he topped a hill doing 90+mph

[Sideways]

Kinda unrelated but my cousin said back whenever he used to race his 240z he got the idea to take the piece from under the radiaror out and race like that to see if it helped any with aerodynamics. Instead of doing that he said it started lifting the front of the car whenever he topped a hill doing 90+mph

Cant say im terribly surprised.  Aerodynamically speaking the Z is pretty pewpy.  That big, open, sexy looking grill is nothing but a huge funnel that scoops up air and pressurizes the engine bay- That pressurized air then pushes up on the not-terribly-small large surface area of the hood, and creates lift.  The idea behind an air dam is it helps block air going under the car- & the idea of blocking off the grill (not all of it mind you) takes that a step further- dramatically lowering the amount of air under the hood.  This helps with drag, lift, and even cooling (Remember the only thing that "moves" air is air pressure differentials, ie air always moves from a high pressure area to a low presure area- when youve got a lot of high pressure under the hood, you have to "push" that much harder to get air through the radiator and into the engine bay.  Reducing the amount of air in there can reduce the amount of pressure in there, which makes it easier to move air through the radiator).  Its not hard to imagine that the panel your cousin removed would allow more air in/under the car exacerbating the issue

Edited April 11, 2014 by Sideways

[Gareth. J.]

Does anyone reproduce the factory versions in particular the fibreglass type fitted to the 432's ?

[260DET]

About 20 years ago when I first got into Zeds took some pics of a variety of S30's doing circuit laps. Once it was noticed, the difference between those which had just front air dams and those which did not was obvious. The air dammed ones stayed fairly level on the track, the naked ones were nose high, they actually lifted up front at speed quite noticeably. That revelation began the quest for best Z aero.

[roger280zx]

^^^^ And now you race a zx, problem solved.