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polished cai vs painted cai

Thread: polished cai vs painted cai

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2011-03-04 19:53:47
#1
polished cai vs painted cai
im not too sure where to put this, so its here. move it if it would be better in a different section .

now i have ordered a cai. i remember having a polished aem on my b15 and that thing would get super hot. i soon switched to a place racing and the pipe wasnt as hot as the aem after driving spiritually.

is it my imagination that the pipe was cooler when painted or not? i want to lessen my intake temps as much as possible before it really starts to heat up around here. is there a particular paint for it, or does polished aluminum transfer heat better, or ?
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2011-03-04 20:01:09
#2
Originally Posted by lshadoff
Nissan Forums: Nissan Forum - View Single Post - Painted or polished CAI question?

Let's analyze what goes on heat-wise with a CAI.

Heat sources:
Hot under-hood air outside the CAI
Cool air inside the CAI

Heat flows from the hot side to the cold side; the hot under-hood air heats the CAI pipe. The metal transfers heat to the cool air flowing through the inside of the pipe. This sets up an equilibrium of heat flowing through the metal and heating the air that touches the metal on the inside. The rate that the air can carry heat away from the metal depends on the temperature difference between the metal and the air. But the air is flowing through the tube, so cool air is entering and is carried along the tube into the engine. Since the flow through a CAI is laminar, there is no mixing of the air inside the tube, so the air which is near the metal, stays near the metal. If we look at the boundary layer of air as it travels down the pipe, it is heated by the pipe until it is nearly the same temperature as the pipe. Air does not transfer heat through itself nearly as well as the metal transfers heat to the air, so there is a thin layer of hot air travelling down the pipe next to the pipe.

So what do we have? A cross section of the air temperature part-way down the pipe will be a layer of warm air (close to the temperature of the pipe) near the pipe and mostly cool air running down 90% of the pipe.

When the flow of air through the tube is slow, the warm air layer thickness increases because there is more time for the air to heat nearby air, and when the air flow increases, the hot layer gets thinner. On the average, at WOT the average air temperature may rise 5-10% of the difference between outside air temperature and under-hood temperature.

For example, if it is 75* outside and 125* under the hood, the average air temperature entering the engine would be 75 + (125-75)/20 = 77.5* to 75 + (125-75)/10 = 80*

If the flow of air through the pipe is turbulent (constantly mixing), there is fresh air constantly contacting the pipe, and the average air temperature will be much higher.

If you can slow down the heat transfer rate from the under-hood air to the metal tube, then the inside of the pipe will cool down and will not transfer as much heat to the air. An insulating layer on the outside (or inside) the pipe will allow cooler air to reach the engine.

Lew


after an hour i finally found this. thoughts?
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2011-03-04 20:07:38
#3
Honestly, I loved my painted CAI for its thermal properties. It didn't seem to heat soak as bad as the polished units do. My AEM is also painted. For the most part I use powdercoated or primed/painted pipes inthe engine bay. I don't think though that the difference in HP or air temp from this is going to make any noticeable impact vs. the gains that the CAI is getting you.

Brent
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2011-03-04 20:20:01
#4
thanks for the quick reply coach. im honestly trying everything to get these intake/operating temps down. according to the obdII plug and this software my cousin has, im getting 120F intake temps on a 100% stock car. trying to do everything i can to reduce that number to increase efficiency and mpgs for the most part.
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2011-03-05 01:23:01
#5
Wrap the intake with cool it thermal tape and the temps should never be an issue again.
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2011-03-05 01:26:50
#6
"cool it" thermal tape eh? interesting.
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2011-03-05 01:33:58
#7
Originally Posted by Pretty
Wrap the intake with cool it thermal tape and the temps should never be an issue again.


would look ugly as fawk....

try like uh hi temp paint? a good couple coats? like the kuind that can take 1200*
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2011-03-05 02:11:30
#8
i dont think it needs to be THAT high. just something that will go up to 300 degrees tops. gonna paint the sucker with some ahesion promoter, high temp primer, and some gloss black engine enamel paint. when i had the place racing cai, it was some sort of high temp enamel from what i remember.

the intake manifold on my current car is plastic, so heat dissipation from that to the intake isnt critical
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2011-03-05 13:56:03
#9
bahhhh use what we use in PR use a nice looking PVC electrical bend curve and cut it according the routing and thats all mine doesnt get hot never! because plastic reflects the heat faster than metal... Try it and i'm sure you will like it.

here's a post i made in the old forum about this kind of intake... and i know is ghetto but works...lol
http://www.sr20forum.com/classic-se-r/228890-my-new-pr-pvc-cai-installed.html#post2263161

and this is a pic on how it looks in the VE now its the same one.
closed

open
Last edited by joelosr20 on 2011-03-05 at 14-19-59.
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2011-03-05 14:05:28
#10
It doesn't really need to be high temp paint, I have gotten away with home depot rattle can paint on my ad22's, its been on there 2 years and its not fading or cracking, I have also painted my ebay wai with the same paint and no problems there either
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