Colder intake air vs shorter intake path?

[240sxed]

Well Im kinda confused theres many people saying diff things about cold air intakes.

Counting out the bad part about it raining, which would be better? and do you have any personal experience with the rb in particular and a CAI?

I was thinking about running a 45 degree bend just down around where the stock side mount is since I have an FMIC setup now. But my buddy was telling me its longer, so air has to travel farther so it negates the coldness of the air, plus that the intercooler takes care of it?

Just discuss i guess?

[Joe]

cold air on turbo = pointless

the turbo heats the air anyway, hence the reason for an intercooler. why take ANY risk of having your turbocharger, wich will move a TON more air than just a NA engine, suck water up.

[fallen180sx]

whatchya think the intercoolers for?

[RB20 Mistake]

I agree with the above statements. The shorter will allow more air to be sucked into the turbo whereas a cold air intake will allow less air and more strain on the turbo while a minimal change in air temp.

[Andrew85cm]

Actually hot air for example from the intake that lies in the engine bay right next to the turbo/exhaust manifold (as ours does) does increase the temperature of the intake air. Hot air going in and even hotter air coming out. That's just how it works. The air coming into the turbo increases by a certain increment.

I am getting some of this from sport compact car so excuse me while I quote.

This is the formula for that increase:

Temperature rise = T(in) x ((pressure ratio^0.238) -1) / Compressor Efficiency

The temperature for this formula has to be in Ranken which is Fahrenheit + 460. The boost pressure has to be added to 14.7 which is atomospheric pressure.

Anyway using this formula which is accurate you can see that at 60 degrees the final temp is around 188 degrees going into your engine and increasing that to 100 degrees F. gives you about 238 degrees. That is quite a difference. I didn't do all the math you can thank SCC for that but I thought I would share this because it does apply and is true. Same goes for the intercooler which will only cool it down a certain amount according to the temp going into it. So sorry to tell you but you are wrong on this one Kamin. Actually its even more important for a boosted motor to have colder air cause the turbo makes it even hotter. Hope this helps I'm sure you can find the article on SCC website its the Oct 05 issue.

As far as length affecting it more or less than cold air. I don't know the answer.

~ANDREW~

[Joe]

i knew the mathmatical argument would come up, and yes technically thats correct, in a perfect world. its a very rare sight to see a "cold air" type setup on a turbo car because the risk/work involved far outweighs the gain. and intercooler efficencey is also heavily based on ambient temprature, more so than charge temps. i mean honestly, if it was a mod that made a big difference, why dont you see it on many vehicles?

if your trying to get a cooler charge to your filter think about ducting from fresh air rather than sticking the filter where it could be exposed to elements.

[240sxed]

i knew the mathmatical argument would come up, and yes technically thats correct, in a perfect world. its a very rare sight to see a "cold air" type setup on a turbo car because the risk/work involved far outweighs the gain. and intercooler efficencey is also heavily based on ambient temprature, more so than charge temps. i mean honestly, if it was a mod that made a big difference, why dont you see it on many vehicles?

if your trying to get a cooler charge to your filter think about ducting from fresh air rather than sticking the filter where it could be exposed to elements.

Hmmm that does sound like a pretty good idea

[themadscientist]

I am all about using every shred of trickery possible, it all adds up. Of course sucking up water is bad so don't mount it low. In fact by putting it down near your intercooler you are cheating the intercooler out of valuable air. There should be no place where incoming air can escape passing through the core. Mount the inlet for your CAI up front behind the grill and insulate the pipe with heatwrap and foil tape to reject underhood heat.

[Andrew85cm]

I'm not advising to use a CAI cause I wouldn't. I was just saying that as far as if it helps it does help to have cold air. My preference is to duct in cold air too. Actually currently my filter sits right next to my turbo so I was just filling in what is the best option. I want cold air and no water but you won't see me sticking a filter in my wheel well. I was just explaining that cold air is better on a boosted motor.~ANDREW~

[Wulfgang]

I fail to see any "risk" with a CAI, as long as it is properly mounted (not too low). Just do what Nissan did: mount the filter in the engine bay and make a box that takes in air from under the fender and bumper cover. There is no risk of rain droplets ruining your turbo, if that's what people are thinking. The filter will turn any rain droplets to nothing more than droplet-free humid air, which is perfectly acceptable.

As for length of intake piping, it is critical in terms of heat transfer. The intake charge temperature will rise roughly proportionally to the area that the air sees along the pipe (length x circumference). So length does matter. And so does velocity. Intake temperature will also rise roughly proportionally to air velocity. I have seen people claim that the air is moving "too fast to pick up any heat" and that is simply not true. The faster the air moves, the more it heat it will pick up.

As far as Andrew's numbers being right in the real world... where do you think those numbers come from? What do you think an "efficiency" number is? It's simply a fudge-factor to get the theory to match the real world measurements. That applies to intercooler and compressor efficiencies. The same is true for heat transfer coefficients, which are almost solely based on real experiments. So let's not have any arguments of theory vs. the real world. The fact is, the original theory has been corrected to accurately reflect what happens in the real world.

[s14 2510's]

My friend has a cold air and has wrecked over 15 mass air sensors. 13 at $84 a pop adds up. I have got him a few from cars on the lot at work but he still wrecks them when it rains. If you plan on running in the rain its just not worth it. Get a fake headlight if you are that woried about cold air to your filters. Then you can put it in when you go to the track. Its sad looking at the big pile of junk mass airs in his garauge.

[rbsileighty]

I fail to see any "risk" with a CAI, as long as it is properly mounted (not too low). Just do what Nissan did: mount the filter in the engine bay and make a box that takes in air from under the fender and bumper cover. There is no risk of rain droplets ruining your turbo, if that's what people are thinking. The filter will turn any rain droplets to nothing more than droplet-free humid air, which is perfectly acceptable.

As for length of intake piping, it is critical in terms of heat transfer. The intake charge temperature will rise roughly proportionally to the area that the air sees along the pipe (length x circumference). So length does matter. And so does velocity. Intake temperature will also rise roughly proportionally to air velocity. I have seen people claim that the air is moving "too fast to pick up any heat" and that is simply not true. The faster the air moves, the more it heat it will pick up.

As far as Andrew's numbers being right in the real world... where do you think those numbers come from? What do you think an "efficiency" number is? It's simply a fudge-factor to get the theory to match the real world measurements. That applies to intercooler and compressor efficiencies. The same is true for heat transfer coefficients, which are almost solely based on real experiments. So let's not have any arguments of theory vs. the real world. The fact is, the original theory has been corrected to accurately reflect what happens in the real world.

I agree with the box in the bay idea. Keep in mind that as some say "you have an intercooler that's what it's for..." the temp rise is based your initial temp as you move through the system... starting with a cooler temp will lead to cooler temps at the manifold.

I'd say build a alum box in the bay and put the filter in it... similar to this... but I think aluminum would be better

Longer piping for the filter might help the compressor by providing laminar flow... not sure though... just a thought


Modified by rbsileighty at 8:53 PM 9/7/2005

[Andrew85cm]

That box looks pretty good and a decent idea kind of like stock. I'm gonna fab one up when I go home for Oct break from school. My friend's dad has a sign shop with tons of aluminum.~ANDREW~