Air movement in closed engine bay

[Jack_and_MLE]

Hello

I have a Caterham 21 with a VVC-R engine, which is basically a VVC engine on direct to head roller barrel throttle bodies.
The issue I am experiencing is the temperature in the engine bay is quite high so I want to improve the air movement inside the engine bay whiles on the move.
The car has a flat floor, IE, the engine bay is covered by an aluminium skin, which helps with aerodynamics but not with heat issue.

What I am not not sure about is the orientation of the louvres for the best air movement effect.
Would it be better for the louvres to "scoop" the air from under the car or the hot air from inside the engine bay to be "sucked" under the car?

Cheers

Jack

[Sam_68]

Jack_and_MLE said:

Would it be better for the louvres to "scoop" the air from under the car or the hot air from inside the engine bay to be "sucked" under the car?

I'd suggest that you try to arrange it so that air comes in at the bottom and vented at the top, because hot air rises and your worst problems with engine bay temperatures tend to be at low speeds, when little air is being forced trhough the engine bay by aerodynamic effect.

Ideally, you want to duct air in from underneath at a point that is at high pressure, when the car is moving, and duct it out the top at a low pressure point, so that aerodynamic effect also increases the flow.

What you certainly don't want to do is have air being drawn in at the top and forced out underneath the car at high speed, as this will increase lift.

actually working out which areas are at high pressure and low pressure is the tricky bit, but with a bit of ingenuity and a cobbled- together liquid manometer, you can work it out by experimentation if you are so inclined.

[pigeondave]

Hi,

Interesting thread. If I were to purchase a manometer what sort of range would it need?
Would I expect to see a 10Mb difference across a bonnet or would it be more?

[The Black Flash]

Isn't the normal thinking that it's not getting air in which is the problem, it's getting it out? So ducts to scoop it in might not be the first port of call, rather focus on ducts to suck it out.
Flared side panels (with air exits at the rear) are a common approach.

[one eyed mick]

Black flash you are bang on ,it is a problem with I woulld say every 7 type car out there to greater or lesser levels. Flaired out side panels are are an elegant way of acheiving through flow along with rearward facinng louvres and bonnets rased slightltly at scuttle ok it will not endear you to the traditionalis t but it will redce engine bay temps greatlly

[Sam_68]

pigeondave said:

Interesting thread. If I were to purchase a manometer what sort of range would it need?

Purchase? Purchase did you say?!

You're on the kit car forum now, boyo - you don't buy one, you cobble one together from bits of clear plastic tubing, gaffer tape and coloured water!

All you're interested in is whether there's a difference in pressure, so you basically just run a bit of clear pipe from one point to the other, via a U-shaped bend somewhere in the cockpit where you or your faithful servant can observe it. Bit of coloured water in the U-bend. Drive the car forward in a straight line at a steady speed and observe - the water level will rise on the side connected to the lower pressure area and fall on the higher pressure side.

The Black Flash said:

Isn't the normal thinking that it's not getting air in which is the problem, it's getting it out?

Indeed, though that's usually 'cos the engine bay is open at the bottom and (very often) the radiator itself doesn't have a sealed exit duct, so there's plenty of air flowing in through the radiator (albeit getting warmed up during its passage though).

If you've got a completely closed undertray and wheel wells, and a closely ducted radiator you may need to consider getting the air in as well as getting it back out again - though why someone would want to build a car like that is beyond me, as it's asking for overheating problems (...an obsessive aerodynamicist might do it, but then they'd consider proper, ducted engine bay cooling as part of the package too, if they knew what they were doing).

[Jack_and_MLE]

In the engine bay there is two struts, which after a drive is too hot to touch, this is why I am working to improve the air movement inside the bay.
From the front on the car, the only air in is via a scoop for the radiator. Above the radiator there is two "nostril" which when the fan is working you can feel air going out from. On either side of the car there is one air outlet. There is an engine tray which closes the bay from the bottom.
The wheels wells are separated from the engine bay by an aluminium skin.
There are a few pictures here http://www.caterham21.com/index.php?mact=Album,mff... which would show the car with open bonnets.
Those are the louvers I was planning to use.

From your comments it seems that I need to fit them for maximum effect facing rearwards and upwards. [url][img]]
Is that correct?

The other part of this exercise is to feed cooler air to the engine and from your comments, I think I could fit a couple of ram pipe on the air dam and with a pipe channel the air closer the throttle bodies.

Cheers

Jack

Picture taken from CBS

Edited by Jack_and_MLE on Wednesday 26th October 20:16

[Furyblade_Lee]

I had a similar issue on my Phoenix. Flat floor etc, at 90mph my bonnet was trying to lift itself off tiling up forwards in my line of vision!! it was stretching the 4 stainless bonnet springs by 2 or 3 inches! Problemo...

I cut a hole in the bonnet just behind and above the radiator, which the Phoenix has a dedicated angled panel to cut out luckily if you wish. This ensures once the negative outside pressure sucks much of the air out, it has already passed through my rad. I then drilled about a dozen holes on the rear edge of the bonnet near the scuttle, again the Phoenix design conveniently had a 45 degree surface ripe for this. Immediatly this stopped the lifting so it did the trick, but I still added 2 secure bonnet pins.

Remember too your transmission tunnel is an escape route for underbonnet air pressure, MAKE SURE if you run a totally flat floor you do not have a "parachute effect" by the rear bodywork. You need to make sure there are slots or holes / vents at the back to let it escape . If you do have a flat floor around your diff and a diffuser, try leaving a gap between your flat floor / rear diffuser and rear bodybork so that tunnel air can escape over the top of the diffuser. RAW confirmed this recently when they put their Phoenix demo car in the MIRA wind tunnel.

Mel, the old owner of RAW flared the engine bay sidepods on his Striker out creating big slots, and reported his Sriker gained 5 mph top speed! So it can be a big issue thats for sure.