Cold Air Intake

[djr81]

but if the temp going into the pod is 10 degrees higher i bet it won't be 10 degrees higher after the cooler. i bet it will be less than 10 degrees higher.

also, if you have a stock bov, it will be recirculating cooled air at idle, so that will keep your intake temps down and help with heatsoak. heatsoak is just caused by heat radiating from the engine and radiator into the intercooler

To deal with the second point first.

There is only manifold vacuum at idle, so your BOV should be shut & the turbo doing nothing of any note. In any case the intercooler cannot cool air below the ambient air temp. Heatsoak in the intercooler is caused by it ingesting hot air rather than from radiant heat.

To deal with the first point second, this may explain things somewhat. Or it just may give you a headache. It is a datalog of a road test with thermocouples hooked up to various points in the car. Pod was unshielded.

Conditions: Ambient 15 deg. Drive down hwy at 100 k's, brake and accelerate from 2nd gear throught to 8000 rpm in 4th, cruise for about 30 sec and the accelerate from 3rd gear to 8000 rpm in 4th. Stop and idle for about 45 seconds shortly after.

Temps at 8000 rpm in 4th for first test:

air filter 48 (blue)

after turbo 117 (pink)

after I/C 45 (yellow)

throttle body 51 (cyan)

Temps at 8000 rpm in 4th for second test:

air filter 47.3

after turbo 122.6

after I/C 45.9

throttle body 53

Temp at air filter after stationary at idle for about 45sec was 84 deg! Thermo fans switched on and filling engine bay with hot air obviously.

So, based on the above results for the second test lets to some 'what if' scenarios based on different inlet temps to see what effect they have on the after I/C temps.

Intercooler efficiency = 71 %. Temp rise across turbo = 75.3 deg. Using these figures some calculated and an ambient temp of 15 deg, after I/C temps are:

Assumed inlet temp/Calculated after I/C temp

15/ 36.6

20/ 38.1

30/ 40.9

60/ 49.5

80/ 55.3

[lighty01]

IMO

When the air is cooler when it enters the turbo, the more denser it is (holds more oxygen and watever helps combustion) before it is compressed. When it gets compressed the temp still goes up but you would have more o2 going into you engine than if you had warmer air entering.

SO the more 02 you can get in the more power you would get and i guess the better the o2 in the engine would burn.

I'm no scientist but i have a suspicion im correct in saying this. Although i have been wrong b4

Anyways! i want to make one soon =)

[GeeTR]

you will get heaksoak with or without a cai feed, as the act of compressing the air heats it up. i have been trying to find out what happens to the temp of air when it is compressed while the air is hot or cold but i can't find any info about it. it may be like water where hot water cools/freezes quicker than warm water.

if you have a good intercooler then it should be working well enough to compensate for any difference in intake temps.

Hoorah, another CAI thread. I swear those 3 letters and some foam are the seemingly holy grail of unlimited, almost free power to some hahah.

Heating air up, isn't the same as heat soak. Heat soak specifically describes when latent energy moves from one medium to another. In this case, its the engine bay heat, moving into the air box / intake piping, and then into the intake charge

This is exasperated when the car is stand still for obvious reasons. A CAI works simply due to the partition slowing the heat energy movement from engine bay into the air immediately around the pod.

As mentioned, a CAI's main function i think, is not the temp drop at the compressor inlet from 50/80^o to ambient (if setup is perfect with insulated intake to the turbo) but its ability to prevent heat soak when standstill; that is to provide more even temps and give a more consistent feel to the car. Every turbo car iv been in, takes a massive response hit after sitting still in a 40^o day for a few minutes. Those with properly setup CAI's always seem to preform better.

[RBwhatever]

So, based on the above results for the second test lets to some 'what if' scenarios based on different inlet temps to see what effect they have on the after I/C temps.

Intercooler efficiency = 71 %. Temp rise across turbo = 75.3 deg. Using these figures some calculated and an ambient temp of 15 deg, after I/C temps are:

Assumed inlet temp/Calculated after I/C temp

15/ 36.6

20/ 38.1

30/ 40.9

60/ 49.5

80/ 55.3

So I can understand the percentage of the temperature drop across the intercooler. But that also has to be a variable percentage does it not?

Say for instance the car has been driven hard and the intercooler has sustained a fair amount of heatsoak, would that not make its cooling efficiency drop?

Also too for the turbo. The temperature rise across the turbo also has to be based on variable percentage. If the turbo was up to heat xxdeg, it wouldn't be just a matter of adding xy degrees on top regardless of ambient temp. Cooler air would take longer to heat and the air is only passing though the turbo for a certain length of time. Then there's the compression of the the air also, wouldn't that add heat also to the air temp?

[djr81]

So I can understand the percentage of the temperature drop across the intercooler. But that also has to be a variable percentage does it not?

Say for instance the car has been driven hard and the intercooler has sustained a fair amount of heatsoak, would that not make its cooling efficiency drop?

Yes, see the data log of the two laps for your answer. The calculation was merely indicative

Also too for the turbo. The temperature rise across the turbo also has to be based on variable percentage. If the turbo was up to heat xxdeg, it wouldn't be just a matter of adding xy degrees on top regardless of ambient temp. Cooler air would take longer to heat and the air is only passing though the turbo for a certain length of time. Then there's the compression of the the air also, wouldn't that add heat also to the air temp?

The more you compress the air the hotter it will get. This is true irrespective of the inlet air temperature or pressure. It is why compressor maps are shown using a pressure ratio on the vertical axis. As a general rule air doesn't pick up much temperature from being in contact with pipework etc. (take a look inside your intercooler to see how much gear is inside to allow for the heat transfer) But it most certainly does when it is compressed by an inefficient turbo compressor - even the good ones only run to about 80% efficiency ie 20% of the output is just heating the air.

[WogsRus]

Being a mechanical engineer, I can't be bothered filling in the gaps.

BUT the CAI box is like stated designed to reduce heat soak into the pod and keeping the hot engine bay gas out of the intake system.

The transmition form the engine to the cooler pipe through the cooler wall, is insignificant, as there is always air moving through it, hence the reduced boundary layer, means air does not really heat up much.

In my case, the HKS pod is BIG and when in traffic, it use to heat up heaps, and the car was sluggish, inconsistent and generally crap.

Once fitted with the CAI intake temps were reduced dramatically, I have a log somewhere. This is mainly due to the fact that the heat from the engine bay is not being ingested by the intake system, and traveling through the I/C and so forth.

With the addition of thermo foam to my CAi and sealing it off a bit better from the engine bay, the car is even better.

During summer this year, when the outside temp was 38 deg c, the CAI only saw a 2 degree rise in intake temp; this is great, this is stationary too BTW.

Anyway, it does help the car, but it is not necessarily measured in power, it's about response, drivability and consistency.

Edited August 16, 2007 by WogsRus

[Bass Junky]

A CAI is there to enable the engine to be fed COLD AIR (or ambient air) from outside the car.

Air that comes from around, say a pod filter, from inside the engine bay is always going to be hotter than air from outside the car.

A partition really only sheilds from RADIANT heat from exhaust manifolds and the like.

An intercooler works more like a HEAT SINK in that it stores heat until it can store no more and then passes that heat back into the air stream.

for instance... Ambient air = 40... Intake charge after turbo = 120... Throttle body = 50... The intercooler have taken the heat energy from the charge air of 70 degrees. This will in turn heat up the cooler itself.

Let's say then that the air stops.. Intercooler core temperature has risen to 60 degrees. The additional 20 degrees over ambient must then be passed back into the charge air.

Obviously the intercooler passes air temp to the atmosphere also, but for the purposes of this explanation, who cares.

CAI = air from atmosphere not hot air from engine bay.

Partition = shield from radiant heat

Intercooler = heat sink for charge air.

BASS OUT

[bugger]

So is there anyway I can DIY CAI??? if, so how? is there any pics to show examples???

How much to do it?

[djr81]

So is there anyway I can DIY CAI??? if, so how? is there any pics to show examples???

How much to do it?

Sheesus. You have a thread bung full of mechanical engineers (yes, guilty as charged) banging on about thermodynamcis & heat transfer & you want practical advice on building things?

[TTT]

LMAO at these threads.

I'm not a mathamagician or an engineer or a science teacher or a rocket scientist as some people on here obviously are.

so... in regular human terms.

if you must have a pod - extend it "OUT" of the engine bay.

if you don't care if you have a pod or not - use a stock air box and search these forums for "REV210"'s post about a solution to stop the intake pipe sucking closed.

Street car - stock air box.

try to improve the stock air box if you want.

in the R32 GTST, the duct goes from behind the headlight in to the bottom half of the box.

easy to mod.

if you get a FMIC, there is plenty of room under the air box where the stock IC was to set up a massive intake to the box and all Legal.

The R33 box where the duct goes in to the top is a little more difficult but I'm sure something could be made to improve the intake snorkel or perhaps another duct to the other side on the top of the box.

seriously - the number of people on here using stock air box making ridiculous power is enough to never use a pod.

LEGEND1 - RB20, 300+rwkw, stock RB20 air box.

ABO BOB - over 250rwkw - stock R34 RB25 air box.

MINES gtr - 600hp, r34 GTR stock air box with new ducting.

some people say "My fmic pipes go where the stock air box is so I need a pod"

modify the air box.

Some guy on the Stagea section of this forum modified his stock box to fit around the fmic pipe.

Apart from "it sounds sick wif da pod", what reason do you have for using it on a street car?

I did my own testing of intake temps with a pod, pod with CAI, pod with heat shield and cai and stock air box and a digital temp probe, back in 2002 or 2003...

Feel free to search for it as I had posted here somewhere way back then.

[WogsRus]

my first post has some instructions

[bugger]

Do you think getting off ebay the clear CAI box of 80 over bucks is worth it???

How about the aluminium hose that brings down to the front of the front bumber???

[TTT]

yeh man.. anything from ebay is a great idea.

see if you can also find yourself an electronic supercharger.

or a fuel magnitizer.

[RBwhatever]

Sheet of 1.5mm Aluminium 550mm x 300mm- $5

PVC pipes and joins - $2

PVC Glue - $5

Black Paint - $2

Zippy Ties - you should have some already

Spline - 20c a meter

Edited August 16, 2007 by KeyMaker

[Nismo_God]

i wasted heaps of time fitting a CAI on my pulsar, it was beautiful, flex pipe to pod filter that sat just behind the gap in front bar under lights....perfect setup and nothing....took bloody ages too

[bugger]

Hey guys, just a question...

The air box should keep hot air out of the pod..if the box is black, isn't black colour good conductor of heat? or should i get transparent one?

some physics here i guess.

by the way, i'm not a science student. LOL

[FineLine]

I am mounting my pod under the guard completely isolated from the engine bay. It sounds simple enough but there are traps. The floor isnt level in the corner of the engine bay so care has to be taken to ensure it seals to prevent moisture etc finding its way to the filter.

My local rod builder made me a cone that mirrors the profile of the pod to gain clearance between the tyre and the pod. I am now building a floor for it that will run to the shelf of the blinker vent in the gtr front bar. The cone and the floor will keep the larger objects like stones and low flying jets away and the pod will be force fed outside temp air via the blinker slot.

Thinking of doing sides for it of super fine mesh simply to act as a water diffuser. Gtr geoff has an externally mounted pod and when it rains his airflow readings are shot. I am hoping the steps i am taking will eliminate those issues.

If we were truly serious and not so concerned about rice the optimum is a high mounted snorkel a la 4wd application. Might look a bit dicky on a line but the benefits are all there from a performance perspective.

[khunjeng]

Hey guys, just a question...

The air box should keep hot air out of the pod..if the box is black, isn't black colour good conductor of heat? or should i get transparent one?

some physics here i guess.

by the way, i'm not a science student. LOL

color its not about conduction, its about absorbtion and radiation, for for this applciation I wouldnt stress

Heat conduction is important, thats why platisc and rubber are preferred. Al. is a good conductor and thats why I dont use it in my shield

[bugger]

color its not about conduction, its about absorbtion and radiation, for for this applciation I wouldnt stress

Heat conduction is important, thats why platisc and rubber are preferred. Al. is a good conductor and thats why I dont use it in my shield

Thanks buddy.

Cheers.

[rev210]

The design of a good cold air box has a few more complicated elements to it. As mentioned the positive pressure to feed the intake is important and makes a big difference at speed. Also the volume and internal design of the box is important. Other things too like bell mouths. Notice on the stock unit there is a bell mouth. In testing (although this isn't a very good bellmouth) removing it decreases power and fitting a better one yeilds a little more.

The factory box isn't a shabby design at all. It can be improved on but, a pod in a cardboard cutout designed airbox is going to have a hard time matching it's power under speed unless there is some substancial thought gone into the design.

Most of the average joes & julies who frequent thier local dyno , tune with the bonnet up and don't usually do any kind of road tune afterwards. If you really want a good tune for the last run do the final tweaks 'bonnet down'. It goes without saying a before and after is best done this way too for comparison. The typical claim of increased 'pod power' comes from this very common 'error'.

Dyno's do struggle a little in replicating the airflow of a moving vehicle but, those big ass fans do a reasonable job with the bonnet down on even a mega beast, so give it a shot.