The thread to end all discussion about temp. difference for CAI/SRI!!!

[user]

Well, since I have another hour of wait for my flight, might as well continue on my nerd rampage...

This will evaluate how much you are diminishing oxygen intake due to "heat soak" when using a SRI and how much you are increasing oxygen intake with a CAI.

Your stock airbox is engineered to suck air from a place where air circulates and isn't heated up by the engine too much.
A SRI will draw air directly from atop the engine, at much higher temperatures.
A CAI will draw air from near your bumper, at much lower temperatures.

For the sake of keeping it simple we will suppose that regular intake temperature is 45 C, SRI intake temperature is 60 C and CAI intake temperature is 20 C. If someone can come up with actual measured values, I will redo the calculations to reflect the changes.
We will evaluate each situation using the P*V=n*R*T formula (look it up if you want, it's the ideal gas law). Pressure and Volume will be kept constant (101.3 Kpa and 2.0 L) for the calculations.

n*R*T=202.6

STOCK AIRBOX: T=318K
n*8.314*318=202.6
n=0.07663 moles of gas approx.

SRI: T=333K
n*8.314*333=202.6
n=0.07318 moles of gas approx
that's approx 4.5% less oxygen going into your engine, if it weren't for the added bonus of added airflow, you should be getting 4.5% less HP from your engine!

CAI: T=293K
n*8.314*293=202.6
n=0.08317 moles of gas approx
that's approx 8.5% more oxygen going into your engine on top of the added airflow!

Now, out of curiosity and to validate the results, how much HP gain are you people running CAI getting? Again, the temperatures I came up with are rough guessed estimates (I think I took too big differences in temperatures), but the difference between CAI and SRI is there...
Of course, there are other values that can affect these results (humidity and things like this) but they should be fairly accurate as long as the temperatures are.

Last thing, if it's cold outside, your CAI temperature will be almost the same as the external temperature, whereas the SRI will retain near engine temperature, further increasing the benefit of going CAI in cold weather.

I apologize for my complete lack of interest towards maintaining significant figures.


Corrected numbers using more accurate data should be up in a couple of days, I'll give this thread a bump, unless someone wants to sticky it?

[Excalibur]

You should pm 02SilverSiHB. He has actual measurements that he took. They were all from the same car and he has results from each one that you're wanting to know about.

[fg2!kid]

i have the dashhawk on my car so i can see what my IAT is. when driving on the freeway, i have a SRI, if my ECT is about 185F my IAT is around 80F or so

[fg2!kid]

also the IAT reading is done at the MAF sensor, in my opinion i think a ram air intake would be the best bet of getting the most dense air with a CAI the leangth of the piping it gives the air time to heat up maybe not alot but iam sure it does i really would like to put a temp sensor at the TB i think that would be a great place to get IAT readings then we could really put all these intakes to the test. i myself have been thinking of all kinds of designs for a great intake its not easy there is so much to consider

[Tredd]

Originally Posted by user

A SRI will draw air directly from atop the engine, at much higher temperatures.
A CAI will draw air from near your bumper, at much lower temperatures.

I think this is were most people will have dispute. I would think this is right when the car is sitting still, but when the car is moving, the hot air around the engine bay moves around too, theoretically out of the engine bay. I have been thinking about this, and if you remove that plastic thing ontop of the radiator and throw on some hood spacers, the engine bay would be significantly cooler when going at higher speeds due to the greater areas for hot air to escape. I would think that SRI's suffer more from the metal of the SRI's heating up inside the engine bay, rather than the hot air inside the engine bay, off course this is when the car is moving. This is what i think, i could be wrong...

[willowofwisp]

well remember this law, the hotter air in the engine bay while moving is gonna try to escape so u can have an equal temp inside the bay and outside, but of course that never happens, i really only see heat soak as an issue when ur stopped at a redlight for several minutes then begin moving again

[fg2!kid]

yea you have a point thats why you see alot of race cars with vented hoods becasuse the air that travels under the car gos into the engine bay

[fg2!kid]

Originally Posted by willowofwisp

well remember this law, the hotter air in the engine bay while moving is gonna try to escape so u can have an equal temp inside the bay and outside, but of course that never happens, i really only see heat soak as an issue when ur stopped at a redlight for several minutes then begin moving again

this is true i have seen my IAT get as high as my ECT when at a stop light

[OrdnanceMarine]

Stock Intake Results:

Results from the IAT sensor as read via my ScanGaugeII are about 12-13 degrees F higher than my stabilized outside air temp as displayed on the dash when the car has been at speed for at least a minute or two. Other folks with ScanGauges come up with similar numbers so you've got one scenario figured out.

[redline8500]

i insulated my injen cai and i run about 5-8 degrees hotter than displayed on the dash i have a dashhawk

[fg2!kid]

Originally Posted by redline8500

i insulated my injen cai and i run about 5-8 degrees hotter than displayed on the dash i have a dashhawk

insulated ? what like a heat wrap ? what did you use ?

[user]

I will need accurate intake air temperatures for stock, SRI and CAI to correctly calculate everything. This will also resolve the issue of whether the air is moving enough in the engine bay to lower the temp on a SRI.

Temperatures need to be taken in a moving vehicle, so all you guys with all those high tech 100000 gauges please get me that data!

[fg2!kid]

ok ill take some readings today

[redvtech07]

^Im in for in the data

[KidnKorner]

Originally Posted by user

This will evaluate how much you are diminishing oxygen intake due to "heat soak" when using a SRI and how much you are increasing oxygen intake with a CAI.

What in your mind is the defintion of heat soak? Heat soak is a term to describe the heat absorbed by surrounding components in the engine bay. Heat soak has nothing to do specifically with the temprature of air that an intake injests. Even a CAI suffers from heat soak.

[redline8500]

Originally Posted by fg2!kid

insulated ? what like a heat wrap ? what did you use ?

i used thermal tec heat wrap its a aluminum foil with fiberglass and then adhesive to stick to the intake it was like 15 bucks at lopers

[Excalibur]

Originally Posted by KidnKorner

What in your mind is the defintion of heat soak? Heat soak is a term to describe the heat absorbed by surrounding components in the engine bay. Heat soak has nothing to do specifically with the temprature of air that an intake injests. Even a CAI suffers from heat soak.

The sri suffers more from "heat suck" then.

[F-1 Si]

Originally Posted by user

I will need accurate intake air temperatures for stock, SRI and CAI to correctly calculate everything. This will also resolve the issue of whether the air is moving enough in the engine bay to lower the temp on a SRI.

Temperatures need to be taken in a moving vehicle, so all you guys with all those high tech 100000 gauges please get me that data!

You have to also consider humidity. I've noticed with my scan gauge a difference in the intake temp is 80 degrees with 20% hum and 80 degrees with 60% hum.

[user]

Originally Posted by F-1 Si

You have to also consider humidity. I've noticed with my scan gauge a difference in the intake temp is 80 degrees with 20% hum and 80 degrees with 60% hum.

Damn, a lot of humidity will add a lot of error to the data. Try to get the readings in the driest conditions possible.

As for the term "heat soak", sorry if I misrepresented it. By that I meant the increase in intake temperature due to the fact that the intake is placed between hot components and the air it sucks should be quite hot.

[fg2!kid]

X style SRI apexifilter


15 mins of driving in the streets lots of stoplights

MAX readings street
ECT-185 F
IAT-99 F
out side temp via dash 75F

MAX reading stoplight
ECT-194F
IAT-127F
out side temp via dash 73F

MAX 35 min of driving on freeway
ECT-183-187F
IAT-95-100F
out side temp via dash 78F

when i got home i lookd at the temp in my area on weather.com it said 77F and humidity 45%