rick_tj

Why do people do cold air intakes on their turbo cars? Isn't the idea behind the turbo to suck in as much air as possible, and then ram it through the intercooler to cool down the air and make it more dense in there? Also, wouldn't the heat in the turbo cancel out any temperature gains you got from the CAI?

On an unrelated note, would it be worth it to have the UIM and LIM on a T2, or even N/a really, ceramic coated? That way, the temperature of the exhaust from the turbo or exhaust manifold on n/a wouldn't really bother the cold air coming in.

Just ideas folks.

-Rick

Kingsfan

iTrader: (12)

that's what i was thinking, but look what they say here...

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/greddy-fmic-kit-stock-airbox-504399/

Node

iTrader: (1)

Its exactly like you tell it. The turbo heats the air up and the intercooler cools it down so the pre-turbo air temp is negligible. I've been told that it makes a small difference but not enough to worry about.

On my t2 I'm just going to run a TID to the stock airbox position and just get a heatshield to try to keep the radiator heat away from it. Maybe a headlight NACA duct or some other ducting to get more air in. I'm also recircing the BOV so I need some room to fit the hose....
Not to mention I don't think a filter would fit directly on the stock turbo with a airpump? Don't have my car with me now so can't check. I miss her

Almost all of my friends w/ standalones (no AFM) just mount the air filter straight to the turbo but they have big bad front mounts and aftermarket turbos and manifolds.



As for ceramic coating the intake manifolds. I am going to do my LIM and probably my UIM too to match.
The LIM is so freaking close to the turbo it has to be getting heatsoaked like the rest of the engine bay, but the air is moving so fast that I doubt it picks up as much of that heat as you think.
And the UIM is just picking up the radiant heat from the top of the engine instead of the turbo

rick_tj

The plan for me was to upgrade to an s5 turbo for the s4 t2 I'm going to buy. I want to dissassemble the turbo and have the compressor and hot side housings as well as the LIM and downpipe ceramic coated. I figure that way most of the heat will be exiting the engine at a pretty good clip, and anything else won't be able to bother the intake air.

Carzy Driver

I mounted a cai on my TII and N/A in front of the wheelwell with a cone filter inside a aluminum box with a front baffle to keep road water from actually getting to the filter. Now this is just my opinion on this matter but I thought that colder air outside engine bay, colder slightly denser air entering the turbo, maybe slightly lower the output temps, even if it's only 1-2 degrees. Either way I had fun putting the cai in place so really that's all that matters.

SonicRaT

iTrader: (6)

Consider the ammount of air that moves through the turbo versus the surface area of the inside of the compressor housing. You're not going to get too much heat from soak. Most of the heat comes from the compression itself, and is heat rise based upon the adiabatic efficiency. Having cooler air to start (considering you can cut off almost 75* or more in some cases) is always better, how much depends on a lot of things (size of the IC, how it's tuned, etc)

Node

iTrader: (1)

just make sure that the ceramic coatings don't effect the clearnace of the turbine and compressor wheels.

I'm also unsure as to wether its fine to just coat the outside of the hotside as that heatsoaks the castiron and traps the heat in, whereas if you coat the inside then it will not let it into the cast iron. Cast iron is very sturdy though, and I'd be more worried about the turbine wheel clearance and if a chunk of ceramic comes off and ***** up the wheel

Carzy Driver

I think he's talking about just having the UIM and LIM coated, not the turbo.

rick_tj

No, I was talking about the turbo as well.

Carzy Driver

Oh ok, sorry Node.

rick_tj

I figured at least on the hot side anyway, keeping everything nice and warm would help the gases scoot right along inside the housing, and maybe help as far as boost goes.

Node

iTrader: (1)

im doing it more for engine bay heat management, my passenger side of engine bay is yellow and bubbley from the leaky ABS (now removed) and the uber hot turbo and precat

its gonna get a ceramic coated manifold, hotside, and downpipe at the least. Hopefully I'll have some very nice sideeffects of more heat to spin the turbo

Carzy Driver

I've seen n/a headers that cracked or blow chunks out because A, the usual high heat of a rotary and B, some kind of a thermo barrier was used either ceramic coating or thermo-wrap. The 2 that blew chunks were typical steel headers with thermo-wraps and the 1 that cracked was a SS header that was ceramic coated. Then again these were used on racing rotaries so a "street effect" could be different.

RotaryEvolution

iTrader: (30)

i would much rather take a good intercooler over a true CAI on a turbo, a CAI is more effective on an n/a, a good intercooler is more effective on a turbo.

NZConvertible

Geez, this is so simple. How can you not get it?

The colder the air is when it enters the intake, the colder it will be when it reaches the engine, no matter what happens along the way. That should be pretty obvious. The only people who would claim a CAI doesn't work or isn't needed on a turbo are those who have zero experience with a CAI on a turbo. Those people should stop posting now...

SureShot

NZ said it. The cooler the air is to start with, the cooler the air temp at the intake port.
Like SonicRat said: turbo efficiency goes way down with warmer input. Conversly, turbo efficiency goes way up with cooler input.

You can even amplify the effect with water/alcohol injection. Putting the nozzle in front of the turbo is hard on it, but the effect is amazing. (like an endless 50 shot of nitrous)

Digi7ech

iTrader: (1)

Put it this way.
For easy numbers(not real ones)

Engine Bay air temp == 100 use "E"
Wheel well air temp == 80 use "W"
Turbo Adds 20 "T"
intercooler reduces 20 "I"

So let's add it up.
E+T-I= final temp
W+T-I= Final temp

Of course that's a VERY simplified equation. The stuff mentioned abive like air density matters too.

jackhild59

iTrader: (7)

*sigh*

What else do we need to know about science & math education in Canada? This is really 8th grade science...

The *whole* of forced induction hinges on the Gas Laws; and for the uneducated or for those of us survived the '70s with long-term memory loss, these laws are not rules that can be broken, they are mathmatical expressions of observed behavior in gasses (air).

Let me try to 'splain in simple terms. Turbos don't 'suck' in air. They create a pressure differential across the turbine, higher pressure on the exit side of the turbine and lower pressure on the intake side of the turbine. This creates air flow that is measured in rate of flow. Volume measured over time equals flow; cubic feet per minute; CFM; as in 'this turbo at x rpm moves y*cfm'. When you correct for temperature you can then calculate a more meaningful measurement- the number of pounds(mass) of air moved. *That* is the measurement you see on Turbo maps, Corrected flow expressed in pounds per minute.

Now all other things being equal, the cfm flow of the turbo at a given state will remain constant whether the temperature of the intake air is high or whether the temperature of the intake air is cool. Thus mass (pounds) of intake air will vary inversly to the increase in air temperature measured in absolute terms (*Kelvin) .

To get a better feeling for this concept, consider a child's toy balloon. At points between the beginning of filling of a balloon and the maximum stretching of a balloon, the change in internal pressure of a balloon is negligible as the balloon increases in size. A balloon is partially filled at room temperature and placed in the sun inside a car on a hot day in summer. The balloon expands in proportion to the temperature. When the same balloon is take out of the car and put into a home freezer, the volume of the balloon decrease. There is still always the same mass of air in the balloon.

BTW unless you have air leaks, turbo intake airmass=turbo output airmass.

So here we are: if the intake air is *hot air* the turbo will be fed by less dense air. It will move the same cfm but less mass (pounds) of air. If the air is *cool air*, the turbo will again move the same cfm but more mass (pounds) of air. The turbo will be more effective, same psi of boost with less rpm yielding less heating of that output air. The boost will come up faster because the turbo is more effective (less turbo lag!!) Yes, the turbo will still compress and heat the air regardless of intake temp but the intercooler will be able to reject more heat because more pounds of air will be flowing through it.

Let's put some real numbers on it:

I have measured intake air from under the hood of my n/a at 170* on an 80* day. What does that mean? Using the Complete Gas Law (no, I am not going to type all the calculations, just trust me; Or not). I calculate that the density of air at 170* will be 9.5% less than at 80*. That means each CFM in our conditions has 9.5% less air mass. Now the turbo doesn't know an 80* cfm from a 170* cfm, it just spools based on the available exhaust flow until the wastegate is satisfied with the boost pressure. The *warm air turbo* will have to increase cfm flow by 9.5% to make the same amount of boost psi as the *cold air turbo*. This means on the *warm air turbo* lag will be increased 9.5%.

If the compressor flow rate is shifted to a less efficient part of the compressor map, the compressor efficiency may drop dramatically. The turbo will then work much harder and cause a disproportionate increase in output air temps.

But what about that huge FMIC?

Imagine a turbo that can put out about 12 psi on your engine before it begins to lose efficiency. Maybe with the *hot air intake* the turbo loses efficiency at 10.8 psi. If you have your wastegate set at 12, most of that boost between 10.8 and 12 is just heat. And that means that if you cool that hot air back down in your intercooler, you only have 10.8 psi. (Maybe that pressure drop across your intercooler is just due to heat rejection, not resistance to flow?)

Ever notice how much lag is reduced on a cold early moring drive? How the boost hits so much harder? That effect is mainly due to the increased air density of that nice cold morning intake air.

Summary? Cool air iintake is good. Hot air intake is bad.

Class dismissed.

gxl90rx7

iTrader: (1)

And how is that not 'sucking' air in??

coxxoc

iTrader: (3)

he was jsut saying that gas will move to the area with lower pressure. You could call it sucking if you want b/c negative pressure is vacuum after all.

InMyWhiteTII

He was trying to clear up everything. By taking thses things out of laymans terms, he can explain it easier. Great explination by the way Jackhild

zxert

I've also heard of people ruining headers with wrap or ceramic coating. But that was on N/A LS1s. Basically the ceramic/wrap makes the headers retain heat, which you think is good. BUT, after a few times down the track or at auto-x they get molten hot and very weak and eventually decay, crack, and break into small pieces. Nascar and other racers do it because they have mad bank and can get away with replacing headers. We can't. Also these were on Chevy motors, not rotaries.

I was desueded from buying wrap by all my chevy buddies because they know it sucks.

Now if you want to get heat reflective wrap and wrap your CAI and IC pipes, that might be a plan.

As for the turbo, someone with more experience should handle that.

Just my 8Cents.

Needa13b

I think it is expensive/difficult, but ideally you want to put ceramic coating on the inside of your exhaust pipe. Less heat is then absorbed by the pipe itself, and more heat is delivered out of the engine bay area. The excess heat could then destroy cats/mufflers etc unless they can handle more heat.
Then also you could wrap your intake pipes, shielding the allready reduced engine bay temps.