DCR59

As you will see, I was a bit bored today, so decided to do some temperature trials on my '94 WRX ra.

I bought a temperature probe from Maplins, and fitted it into the standard airbox.
Outside temperature was 8 deg this morning and took the car on a 12 mile route with a mix of fast A and twisty B roads.
The reading was between 18 - 20 deg at all times.

Removed the airbox and fitted an induction kit, placing the temperature probe on the filter face. Same route and temps were between 25 - 30 deg and climbing to 36 deg when stationary.

Test 3, kept the induction kit, but removed the bonnet vent and fitted an induction kit scoop, also removed the rubber trim from above the headlight on the bonnet. Same route again, similar speeds / acceleration / boost, etc, and temps down to 20 - 22 deg.

Test 4 will be the induction kit inside a sealed off box getting cold air from the bonnet scoop and an air feed from the fog lamp cover. But I need to get a sheet of carbon fibre or aluminium to this first.

But this basically shows that an induction kit on it's own is a waste of time - unless you can get plenty of air to it and shield it from turbo and manifold heat. I know that most of you will know this already, but I wanted to see hard test figures to back this up.

mm20515

I run with an induction kit on my wrx ppp i always fell it responds better on cold nights or maybe its just the sound. Have run with it on and off and the MPg is the same there worth just for suck, small cats beware

GrantyBoy

Cold air is denser than warm air. The denser the air the more oxygen it has, more oxygen means better bang for the combustion engine.

Normski

I have a temperature probe permanently next to my HKS induction kit and my readings are a lot different to yours DCR59 (my car is the same shape).

When moving the temps quickly drop back down to 1 or 2 deg C above ambient. My car still has the ducting in the inner wing from the standard set up, this takes air from behind the fog light cover. The filter isn't boxed in (yet).

I was quite surprised by this, you often read or hear about that inductions kits only take in hot air. But this is clearly not the case.

dynamix

iTrader: (3)

The thing to measure is the temperature of the air going into the engine really but I agree. The standard CAI kits are little more than Hot Air Induction kits and will kill performance.

Get a proper feed of cold air to it from the bumper area using a shield cone intake and it will work better or get the filter/intake into the wing for cooler air.

Another option is a Cold Air feed from the fog light surround to the bottom of the standard airbox - works well for me

wez wrx

is it so critical? maybe on a natural asp car, If you think about it when the air leaves the induction it goes to the turbo where it is compressed to the correct pressure! compressing air makes it very hot!! then it passes through the intercooler to be cooled before it enters the cylinders! i would think the intercooler has far more effect than the temp of the induction because your cooling the induction only to be heated again by the turbo! maybe theres some effect when driving below the turbo??? just a thought!!! cud be completly wrong!!!

dynamix

iTrader: (3)

if it is hot before it goes in - there is still less oxygen going in per cubic inch. Then it gets even hotter, the intercooler will cool it a bit - but do you know what temperature the air going actually into your engine is?

If the air going in is cold, it is dense and will get heated up by the turbo then cooled down but it will always be colder than the hot in hot out scenario above and hence create more power/torque.

Information is the key to safe power IMO

dynamix

iTrader: (3)

to give an example:

Ambient Temperature : 10C
Intake Temp using bumper CAI : 11C
Air Charge Temp on WOT: 25C

Therefore the net effect of turbo pressure is a heating of the air by 14C

If the air going in is 25C from your Hot Air Induction Kit - you will get approx 39C temperature of air actually going into the cyclinders.

Would you prefer 25C air going in or 39C air?

wez wrx

Another thought! I know cold air is densor and cooler air in the cylinder is going to produce more power, but what about the effect of a inducion kit on breathing? Some peaple are calling them useless coz they breathe in too much hot air! But surely with one on, the engine breathes much more freely than a panel filter into the muffler box! The intercooler is the last thing in the chain anyway! Im just a bit sceptical when it comes to cold air induction on a impreza!!

wez wrx

I would think the intercooler is cooling the air more than "just a little bit"!!

wez wrx

I have mine heat sheilded and vent removed, runs fine!! Dont know if i would go to the bother of feeding it further!? Maybe it breathe a little hot air on a standstill?! But im happy! dont know if it would be worth the 1 or 2 hp to cold feed it??

Jay m A

iTrader: (2)

But it can only cool to a delta T, as in any given scenario it can reduce temps by xx degrres C. So the colder the air going in, the colder the air coming out.

dynamix

iTrader: (3)

The turbo boost dictates how much air is drawn to a large extent and how much the engine needs. The standard airbox will not restrict airflow if a proper filter fitted up to quite high levels of power.

But do you know?

It is not just power that this effects from what I am informed. It will also reduce the risk of det and the nasty things that does to your pistons.

Butty

iTrader: (2)

Also be very careful with the method of temperature measurement.
Thin sensor cables, sensors mounted in metal components without insulation or tucked under hoses touching metal can all lead to figures higher than they actually are.
Induction and charge temps are lower than underbonnet temps and can easily be influenced if not adequately isolated or insulated.

nick

harvey

iTrader: (48)

DCR59 : Your post is very interesting. From the work I have done I see no point in going with cone filters until somewhere over 350 bhp. Apart from anything else, you loose the advantage of cold air, good filtration (Subject to air filter used) and the snorkle. Removing the snorkle on its own, contrary to Scooby myth is a BAD thing.
If you are going for a cone filter then you must fit a cold air divider to derive reasonable benefit.
Do NOT use aluminium. Aluminium is a good conductor of heat.
I use carbon fibre with a layer of heat mat on the engine side and I have a cardboard template here for the basic shape. This buds up to the bonnet and can be finished off with a rubber seal of the same type you find on door seals for various cars or from "Frosts"
I am happy to send you photos of the template, cut carbon fibre, heat mat and top seal if you wish to contact me by e-mail. There will also be photos of how to get lots of cold air in there. This is applicable to cold air divider and not O/E air box. If you know how to post photographs, feel free to link them on here.

Removing the rubber in front of the bonnet by the headlight is a good idea. More cold air goes over the top of the engine on an O/E set up but with an air box there is more cold air. (You know by how dirty it gets with muddy water marks).

The design intention from Subaru, in respect of air flow was that air came in at the front, through the radiator, over the engine and down the transmission tunnel. This flow was assisted by air through the bonnet scoop.
The grills on top of the bonnet are blanked off deliberately on an O/E car. The area on top of the bonnet is a low pressure area and removing the blanking plate(s) sucks air out. On a standard car this disrupts air flow and under bonnet temperatures will rise. 6-12C There are cases where removing the blanking plate or part of the plate is beneficial but without good test gear you cannot be sure of the results you achieve.
I have never used reversed scoops to force air in as I have doubts about the advantages over a well thought out flow system.

This is true but as dynamix pointed out:
Once you understand what is affecting inlet temperatures it is time to look at temperatures before the throttlebody but that is a topic on its own.

dynamix

iTrader: (3)

From what I have been able to establish the effect of additional bonnet inlet scoops is actually quite negative - it creates positive pressure in the engine bay and stops air coming through the radiator. But, as Harvey says, I have not tested this myself.

I did before and after Delta Dash road dyno runs with my cold air feed and the difference was quite noticeable in both intake temps as well as Mass Air Flow and ultimately torque.