Creating pressure system hot air out of engine bay

[TurboRA28]

Hi all, this is a topic I know absolutely nothing about so hoping someone can shed some light for me.

I have been led to believe that by putting some plate/shield/tray thing under the engine bay that extends to close to the end of the bay that it will create some kind of pressure system and hot air will be sucked out of the engine bay.

Is this the case?



Here is a shot of my engine bay.. So in what area would I need to place said plate/tray/shield thing?

Thanks
Joel

[JustenGT8]

Yup, just look at any factory bay. I'm assuming you don't want to touch the bonnet? and fair enough Could be worth considering a louvered bonnet for track days though as that will also help.

The raised rear bonnet does NOT work as we all know the base of the windscreen is a HIGH pressure zone

An understray based on the stock one but a bit larger and a bit more elegant would be the go

[c2888]

http://autospeed.com/cms/title_Under...9/article.html
http://autospeed.com/cms/title_Under...0/article.html

that should be a start, i've got to go out for some midnight kebabs, you should be good and sleepy by the time you get through that lot

[TurboRA28]

So from the autospeed articles it appears they are rather short and don't extend under the car a great deal.
So no advantage in say making the under tray extend close to the rear of the bay?

[JustenGT8]

LOL like a i said, pretty much like the stock one but more elegant in design

[TurboRA28]

This is a good read -
http://superhachi.com/theory/downforce/

Yeah seems like it Justen, what material do you think is best? A plastic or metal?

[JustenGT8]

Roundy did one recently dirt cheap out of some thick plastic sheet.

For me though, alloy all the way Gives you a better chance of getting the thing sealed well, will be more durable and for me at least,, will work as a light bash plate. I will also be looking to run mine past the front bumper as a splitter and the forces on that means it has to be fair tough.

[Roundy]

and i still have some plastic sheet if you are interested

This is what my undertray looks like



and on the car



That link you posted is also exceptional, very simple terms and spot on.

What you will need to do is experiment with a pressure gauge and fiddle around with the placement of any tray to see what gives the greatest pressure differential.

Mine was mainly a bit of a test to attempt to tidy up the airflow at the front of the car, and maybe encourage a bit more air to go through the radiator.

However i have tested none of this yet!

[DrNick]

It would be awesome if you could get your hands on a manometer and look at the pressure drop across the various air diversion plates in the bay. That kind of stuff is fascinating

[rsdeo]

You need to find negative air pressure to pull the hot air out. You also want to exit the hot air from the sides or top, not the bottom. Air under the car will slow it down when trying to attain top speed.

[GUN METAL]

Joel, I spose the first question is what do you hope to gain by better ventilation of the engine bay are things in there melting ? You probly have significantly more heat load in the engine bay with the tubro etc etc but is it actually creating a problem ?

Yuo may reduce the heat by passive ventilation but completely screw the earodynamics of the car in the process !

If you want to reduce engine bay temps maybe look at things like exhaust wrap of making sure that air from outside is directed say at the turbo first ?

I am interested in improving the aerodynamics and downforce on my car becuase it likes to see the track and this can be completely at odds with engine bay / engine cooling

Roundy i would love to get some of that plastic of you or can you tell us where you got it from?

Drnick, i have a couple of manometers and have allready done some testing on my car, i also find it fascinating.

I am in the process of doing some modifications on my AW11 to releive air from the back / top of the intercooler heat exchanger and radiator and an undertray / splitter / air dam / complete undertray / rear venturi are all on the cards.

I have dabled with some basic aero and hydro / fluid dynamics enough to know that what works in theory doesnt allways work in real life.

Basically want you need to do is essentially design a passive ventilation system to remove the heat. to do this yuo want to duct the air in there from a high pressure source and have it extracted at a point of the maximum differential pressure, this will promote the highest airflow rates 9providing the ducting does not actually reduce the differential pressure.

There are other ways to promote flows like venturis and the like. Unless you have a massive budget something like F1 where you have some VERY fancy CFD modelling you can really only use the basic principals then test them on the car.

[Roundy]

I bought it from a sign place in Bathurst, they had to order it in.

It is ABS plastic ~3mm thickness, the sheet i had to buy was 2400x1200mm.

So a large amount, but wasn't too badly priced imho.