Scientific Question

[stevetubbyturbo]

As some of you will know i was going to intercool my Hilux but after taking to insurance companys i dont think i'll bother as most of them would would double my premium as its classed as a power increasing modification even though it would only add 4 BHP the vehicle giving me a grand total of 101 BHP but the reason i wanted it was to keep the temps lower.

Anyhow i can still fit the air scoop as thats classed as cosmetic and i can do as many cosmetic mods as i like.

But the question is what is the best way to fit it do i

1) have it front facing so it scoops in vast amounts of air whilst motoring along to blow the hot air out under the car and if i did this would it effect the normal cooling of the radiator or help it?

or

2) have it rear facing so hot air is vented out of the scoop so as air is pushed through the radiator the hot air has somewhere to escape from flowing the rule that heat rises?

[Fidgits]

if you were to do #2 - i would reccomend lourves over a scoop - because, a. they will look better, and b. they will work better for the purpose,

[scionic]

That is absolutley amazing that insurance companies there have the gall to raise your premiums for something like that.

They ought to have to PROVE that there is an increase in claims to go along with whatever mod it is you want to perform and then, IF there is they should be able to raise your premiums proportionate to that increase in risk on their part. No other way is fair really. Total BS.... :ffs:

I am glad insurance companies don't even take modifications into account here. They are corrupt and greedy enough as it is without having one more way to rip the consumer off.

[nrgizerbunny]

answers to both of your methods

1. air pressure underneath your car is invariably low. therefore hot air would natually travel underneath as opposed to venting on top (where there is high pressure). By having the scoop facing forwards you increase the pressure gradient, and thus increase the heat transfer properties.

*********TECHNICAL BIT**************

Higher velocity results in higher Nusselt Number, causing greater heat transfer coefficient.

2. The method of having the scoop facing backwards is not as good because the air will still be drawn in the same direction, ie towards the engine. so it effectively doubles back on itself. This results in a smaller pressure gradient and not as efficient cooling.

You will also cause more drag on your vehicle if you employ method 2 as oppposed to method 1.

I have tried to explain what i mean using a diagram below, the red lines are "streamlines" and represent the flow of air. Note the squiggly bits are intended and show "turbulence"

Also while I'm at it, hot air only rises in "free convection". ie cup of tea left to stand. Air flowing through your radiator is "Forced Convection", heated air is forced horizontally and the effect of fast moving air has a greater effect than the air density (this is why hot air rises, its less dense)

[stevetubbyturbo]

I'll give you something mate you know your stuff :bookworm:

Thanks for the diagram that explains it alot better

Cheers mate

[stevetubbyturbo]

That is absolutley amazing that insurance companies there have the gall to raise your premiums for something like that.

They ought to have to PROVE that there is an increase in claims to go along with whatever mod it is you want to perform and then, IF there is they should be able to raise your premiums proportionate to that increase in risk on their part. No other way is fair really. Total BS.... :ffs:

I am glad insurance companies don't even take modifications into account here. They are corrupt and greedy enough as it is without having one more way to rip the consumer off.

←

bit off topic but

I can remember a few years ago i put alloy wheels on my Renault 21 and they were the same size as the standard wheels and the insurance company hit me another £30 because of it

[nrgizerbunny]

thats no problem at all, I was worried you may not understand what i was on about.

just an added note but method 2 will cause more drag than method 1. The majority of people think if an object is wedge shaped its more aerodynamic than a blunt object - this isn't the case.

the chavvy twits with boy racer bodykits on their novas will actually end up having a lower top speed than a normal nova. - planks.

[stevetubbyturbo]

Na its not for speed i just want to get my engine bay temps down as it gets a bit hot in there and the Hilux 2.4 is known for cracking CLY heads due to heat problems

Cheers again mate

[Karma Supra]

nrgizerbunny - Great reply as always!!! Air flow an aerodynamics fascinate me (yeah sad ***** I know) but I don't know a huge amount about them... (well very little infact :D)

Am I corract in thinking that on a much lower vehicle (say a dropped mk3 supra for instance ;)) with a fairly large mouth and a "belly pan" under the engine that ends at the sump (behind front wheels).. when running at speed rear placed louvres would be more effective? (Thinking E type style, one each side of the bonnet bulge)

Bassed on the fact that there will be lots of air flowing over the bonnet, and stratigicly placed louvres would work with a venturi effect drawing hot air out, as well as decreaing the amount of air underneath the car -aiding high speed stability?

I get mega heat soak on a twisty track! (I.e lots of flat out accerlerating, not a huge amount of straight line speed)

Probablya daft question... but hey :D

[nrgizerbunny]

thanks for the compliment! :D

to answer your questions, specifically about your car. Yes you are correct in that rear slanted louvres would improve cooling but:

1. you must make sure that the location is not a stagnation point of air!, a stagnation point is somwhere where the air velocity is zero. On a car this is usually close to the base of the windscreen, on an aircraft its right on the nose cone. A bit of an aside but this is how aircraft measure their speed.

2. Its not as efficient as a forward facing scoop, but the use of a forward mounted scoop would require you to remove your belly pan for decent effects. Rear slats are also more aerodynamic provided they do not protrude.

3. It wouldn't really act as a venturi because its not "enclosed", for example if you take the bottom of the car you have effective closure between the chassis and the road. On the top of the car you don't but you would get heat sucked out through the louvres because you have a belly pan, so this efffectively isolates the engine air from the air moving underneath your car.

hope this helps