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Discussion Starter #1
Here goes..............

I have read on this forum in many different threads that a supply of forced cool air is vital to the engines performance (?) If I was to redirect the air con air flow to the air intake would this help matters (?) |EQU| supply of forced cold air. I know that in its self the air con unit has a negative effect on BHP - at least it has on other cars I have owned.

I am not going to dot his but thought that it was a good oportunity to prove my technical ignorance to all those who have not already figured it out :)

Discussion Starter #2
THe theory is good, but the gains made from forcing conditioned air into the intake will be less than the losses from the air conditioning in the first place! It isn't just the temperature, but the pressure of the air. Positive air pressure (from forced induction by capturing air at speed) is what is required.

Using aircon to cool brakes could be an idea though :)

Discussion Starter #4
What has been done before is to use the air-con to cool an air/water intercooler. This is only really any good though if you can't fit a suitable air/air intercooler.

Discussion Starter #6
It's a bit like opening the fridge door to cool the room down.

It takes more energy to drive the air conditioning compressor than you gain from the cold intake air under steady state conditions.

Would be handy for a standing start mind - cool everything down nice and frosty then switch of the air con just before dumping the clutch.

Standard intercooler with water spray is pretty damn good anyway - copes fine with all the WRC conditions (Safari springs to mind) and 2 bar plus mid range overboost. (higher the boost the higher the air temp from the turbo compressor.)

Discussion Starter #7
Squirt CO2 or nitrous oxide over the intercooler , that wud b cool
Isn't there a better use for nitrous oxide ???

Like feeding it into the passenger compartment...


Discussion Starter #8
Even if you could gain more bhp than used to drive the compressor, it still wouldn't be no good. The a/c de-humidifies the air drastically, therefore being of no help. Dense cold air, if I am correct, (it's possible I'm talking bo**ox again) is what combusts fuel well. A/c delivers non-dense (I don't think that's a word) air.

Also on a more practical note, how the hell would you duct it to air intake/ brakes without completely ripping the bulkhead out and finding new places to re-locate everything.

If you really want stupid, how about fixing a small canister of liquid oxygen near the air intake to turbo, fitted with a spray nozzle, operated by a solenoid valve. O2 boils/ vapourises at about -197 degC at atmos pressure. Cold enough for ya? :)

Discussion Starter #9
Original Post:
The a/c de-humidifies the air drastically,-YES CORRECT- therefore being of no help -NO WRONG BOLX-Dense cold air, if I am correct, (it's possible I'm talking bo**ox again) is what combusts fuel well-YES , CORRECT- A/c delivers non-dense (I don't think that's a word)-NOT A WORD and amp; BOLX- air.

Also on a more practical note, how the hell would you duct it to air intake/ brakes without completely ripping the bulkhead out and finding new places to re-locate everything-YES , U HAVE A GOOD POINT :)

Discussion Starter #10
Thanx Evoboy, I feel like a schoolboy having his homework marked. 5/10?

So what makes air dense, then? Cold air|EQU| dense air, why?

Discussion Starter #11
As air or any gas heats up the molecules move further apart , so less molecules per unit of volume (cubic centimetre etc) means less air so less dense , as a gas becomes colder the molecules move closer together so the opposite of the above occurs.
Simple stuff really , didn't u do this in physics at school ?

Discussion Starter #14
If you don't want water in the engine - why have water injection as a performance mod now and on WW2 airo engines for more power?

Discussion Starter #15
Injecting water increases power by cooling charge and suppressing detonation, this is good if running high boost pressures.

Air with water in it is less dense so less power, but use the cooling effect and this gives more power.

HH6 - you're nearly right, you are thinking of Charles Law - when the pressure of a gas remains constant, the volume of the gas will increase as temp increases, Boyles Law is if temp is constant, press increases as volume decreases.

Oh dear I must get out more often:)

Discussion Starter #16
Universal Gas Equation is the one to use

P x V |EQU| m x R x T

Which is a combination of the others mentioned above.

P|EQU|pressure in Newtons per metre squared. (normal atmospheric approx 101.325 N/m^2)
V|EQU|volume in metres cubed.
m|EQU|mass in kg
R|EQU|gas constant|EQU|0.287kJ/kgK
T|EQU|temperature in degrees Kelvin (Centigrade |PLS|273.15)

So for air density at any given boost


eg. no boost at 20 degrees C. (293.15 K)

density|EQU|101.325/(0.287*293.15) |EQU| 1.204kg/m^3

and at 1 bar boost (1 bar|EQU|100N/m^2) at 45 degrees C (318.15K)

density|EQU|(101.325|PLS|100)/(0.287*318.15) |EQU| 2.204kg/m^3

Playing around with this equation will demonstrate the importance of a good intercooler.
Bear in mind that the outlet air from the compressor can reach up to 150 degrees C.

Power is directly proportional to the density of the inlet air. Colder air is denser! More power.

Next week - building your own interstellar warp drive using an HKS Super Drager and a dozen cans of Special Brew.

Discussion Starter #17
And if you want to work out how much heat your intercooler is removing then you can use:


Q |EQU| heat removed (in Watts)
m |EQU| mass flowrate of air (kg/s)
Cp |EQU| specific heat capacity of air |EQU| 1.005 kJ/kgK at 25 deg C
dT |EQU| temperature difference between inlet and outlet of intercooler

You can then use this as a basis for comparison of different intercooler perfomances or different mounting positions or to see if improved ducting on the front works.

This can also be used to see if the air conditioning route or waterspray or spraying with NO2 does provide any increase in the amount of heat removed and which is best. All we need now is someone to reroute the aircon and we can get some results...... Any takers!!!

Andy (Bored with designing nuclear reactors, much more fun designing intercoolers)

Discussion Starter #18
This is where Simon switches into stupid mode and wishes he had paid attention in school!

Andy, why do we need to know the heat removed by the intercooler in watts rather than just the temperature difference between inlet and outlet of the intercooler? I would have thought that absolute performance was the thing of interest, as the engine doesn't know how much heat has been removed, only what temperature the air is when it gets into the engine! Or am I just too simple? (don't answer that one :D )

Discussion Starter #19
Because that's just too boring and doesn't involve any equations :D:D:D

You are correct though, I just thought seeing as how everyone was going equation mad, I'd add to the fun....
I've had to design a few heat exchangers before and could have gone really OTT with the equations but I thought best not to, so keep it simple (A bit like me really :))


Discussion Starter #20

What is highlighted by the equation is the fairly obvious, but not often taked about fact that as you increase boost, the temperature of the charge is higher on leaving the intercooler. Obvious really, because it is going through it faster and has less time to be cooled! The thing I need to look at is how much this effect is and then try to understand at what point it is worth spending money to sort it. Now what we need is an equation that factors boost, temerature, power, cost of mods and performance gain ;)
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