ChevyKiller

LOL - you are replying to an engineer....

gambi06

Richard,

I'll have to do some digging to find that research. I'm curious if anyone knows at what point in the air's travel is the intake temp measured? (MAF sensor? TB?)
Because if it's measured at the MAF, that's before it travels through the hot intake tract, so the findings might be way off.
And as far as heat absorbtion goes, think of the heater in your car. Yes, the air velocity is higher in your intake, than your heater motor blows, so there is less time for absorption to occur, but it does occur, especially in a metal intake.
This is an age old philosophy. Look at all the high perf. intakes for carbureted v8's. They all have the isolated runners and the air gap in the valley now, because the cooler the air/fuel charge, the better! I'm not saying that what I'm doing is making things drastically better, but every bit helps. And like I said before. Yesterday, I checked once again after driving in 100 degree ambient temp for 30 minutes, my intake and aluminum MAF housing were lukewarm at best. I invite anybody with a metal intake to grab hold of your intake or MAF housing under those same conditions and hold on as long as you can!

gambi06

Well, if he's an engineer, he should know that any reduction in intake air temp (however small) isn't "completely unnecessary".

-gambi06

Tucker

It's measuerd at the MAF and yes your thinking right. Now that air has to pass through 1.5' of very hot aluminum tubing.
How hot is it at the TB? Who knows, but I do know that the tube itself is too hot to touch.
Jay

don_w

I'm not going to get into a deep scientific discussion of heat transfer and heat exchanger design, but let's take a simplified look at this issue.

Assume for simple calcs, that the inlet tube has a 4" dia and is 18" long. That yields a static volume of 226 cubic inches (~0.13 cubic feet). And let's also assume that at WOT, the volume of air passing though the intake tract is 420cfm (or 7 cubic feet per sec). That means that the entire volume of air in the tube is exchanged about 54 times per second (7 divided by 0.13).

In other words, every molecule of air entering the tube is only in there for less than 0.02 seconds. Heat transfer is a direct funtion of time (among other things)... and the amount of heat transfer that can take place in 2/100's of a second is minimal.

And to make it even less significant, is that heat transfer primarily occurs at the interface of the two materials (i.e., on the inside surface of the tube). The number of air molecules that actually touch the metal surface is a very small percentage of the volume passing through it. Heat transfer dimishes greatly the farther away from the surface you get. That's why true heat exchangers (like radiators and heater cores, for example) have small passages and lots of surface area... this is what promotes heat transfer.

The example of the car heater was mentioned above. If it was just a heated 4" dia tube with air blowing through it, it would be a lousy heater. But since it has small tubes and fins with air passing over and through it, that is why the heat is pulled from the water and released into the air passing over the core.

The whole purpose of this isn't to dissuade anyone from getting a plastic intake or wrapping a metal tube to keep it cooler. My only point is to explain why I believe that it's not really a big enough deal to worry about. Some of you may disagree, which is fine. This is just my 2 cents on the topic.

And yes... I do have a degree in chemical engineering.


.

wallace

well then.... that is good enough for me, anyone else is just arguing an opinion or gut feeling. this is also true, it can't be done.

gambi06

Don,
You make a completely valid argument, and in the simplest of calculations, I agree w/ you 100%. But I ask you two things: 1. As the temperature of both of the mediums rise, (ie, the intake tube and the incoming air) wouldn't heat transfer increase exponentially?

2. Since my car spends less time at WOT, (Thanks, Gas Prices! )
What would a more realistic day to day, just driving down the road, CFM calculation reveal at say, 2,000 rpm?

Again, I know these aren't drastic numbers that will yield significant differences in performance, and I don't claim it to be such... it's just the theory of this stuff that interests me! Also, this **** computer in our s197's is soo freakin' picky, it's interesting to see how it acts with all these small changes applied!!

Thanks for your input on this.

-gambi06

don_w

Actually, the opposite is true. Heat transfer is improved as the temp differential (the delta) increases. So if ambient air is hotter and the underhood temp is hotter, less heat transfer takes place.

Think of it this way. Melting ice is a form of heat transfer. If you put an ice cube (at say 20 degrees) on the sidewalk on a 40 degree day and on a 100 degree day, which day would it melt faster? The heat transfer is much more with the 80 degree delta than it is with a 20 degree delta.

Another example is the coolant temp in a car. The coolant temp will be lower in the winter, than it is in the summer. This isn't because the engine temps are lower (the heat of combustion will still be about the same)... it's because the air passing over/through the radiator is cooler in the winter. Again, a larger delta between the air temp and the water temp will remove more heat.


I honestly don't know what the CFM draw for these engines would be at 2000 rpm. But let's say it was 1/4 of the WOT draw (~100cfm). That would mean the air will be in the inlet for 0.08 second rather than 0.02 second. Even if it was 1/10 of the draw (say 40 cfm), the time in the intake tube would still only be 0.20 second (1/5 of a second).

Frankly, the purpose of having a CAI is to increase performance/horsepower. This is generally accepted to be at WOT (or very close to it). Cruising down the road at 2,000rpm is not a situation where it really matters what's happening in the intake.

gambi06

This is true...that was probably a bad example on my part!


-gambi06

Tucker

Don is one of the smartest people I have read posts from, that's for sure, but all math aside let me ask this in laymans terms.

If I can't touch it because it's too hot and its a super conductor (3rd fastest to transfere heat behind gold and silver) where is it transfereing the heat to? Outside air? Inside air? Or both? Can't be only one. Is the flowing air notliterally pulling the heat from the pipe?

If one pipe material (plastic Vs. Aluminum) is upwards of 40-50 degrees or more cooler then the other, wouldn't you think that the air inside will be cooler due to the material surrounding the air being that much cooler?? Take a 4" aluminum pipe and plastic pipe and sit them in the 90 degree sun, then put your arm inside each, which will be hotter inside? Or will both be the same? I have a guess.

And why have we always put bags of ice on our aluminum intakes at the strip? If the air is going through the pipe so fast it doesn't pick up the heat from the tube (theory) then wouldn't that work in the reverse with cooling the intake with ice?? So we have been wasting our time and money on ice?

Many of these questions can not be answered with math, but only by testing. A temp probe would need to be put at the TB and the temp measured to see the difference from the MAF to the TB. This will tell you what the air has absorbed from the material used. Figuring the speed and time air is in the tube is great, but it's still a guess as to what that air adsorbs. Would you agree?

We can use all the formulas in the world, but if it's too hot to touch, common sense tells me what's inside it hot as well.

Thanks
Jay

ski

Actually, aluminum is the 4th best conductor of heat. Silver is first, copper is 2nd, and gold is 3rd. (Also, note the extremely low thermal conductance of air):
http://www.engineeringtoolbox.com/th...ity-d_429.html

(1) I agree that static air inside an aluminum pipe that's exposed to the sun with a 90 F ambient temperature will be eventually become hotter than the static air inside a plastic pipe under the same conditions. However, even this heating process will take some time to occur due to the extremely low thermal conductivity of air.

(2) As previously stated by Don, the air in the subject of this discussion is not static. It's flowing extremely fast thru an aluminum pipe(CAI), which in turn limits each air molecule's contact time with the CAI's surface to a few hundredths of a second.

(3) Also, as previously stated by Don, of the total air volume that's flowing thru the CAI, only an extremely small % of it that's located in the boundary layer immediately adjacent to the CAI's surface will conduct any heat from the CAI.

(4) In summation, air has an extremely low thermal conductivity, the air is flowing extremely fast thru the CAI, and only an extremely small % of the total air volume has an extremely limited contact time with the CAI's surface.
Thus, one can conclude that there will be only a miniscule increase in the air's temperature after flowing thru the CAI.


The key to getting a N/A S197 to run faster 1/4 mile times is not to cool down its CAI or its intake manifold, but instead to cool down the air that flows past its MAF sensor. This cooler, denser air not only allows the ECU to send more fuel per unit time thru the injectors, but it also prevents the ECU from pulling timing in order to prevent pinging when hotter air is ingested. And both of these produce more hp.
How does one cool down the inlet air? By cooling down the entire engine compartment. Open the hood, and allow the engine and other components to cool naturally, or use fans with or w/o ice.
Cooler components = cooler air flowing past the MAF sensor = more power.
Another tip that may help to run faster times is to reload the tune. This wipes out any conservative timing and A/F data from the ECU's long term memory tables due to its adaptive learning algorithm.

Tucker

If you read my post clearly you would see I have stated I understood Dons post about static air Vs. flowing air
and
How fast it's flowing
and
the volume,

But what my questions were about common cense and actual facts of air that has been tested.
Saying it's going too fast to pick up heat doesn't mean it's true.

Until someone tests the theroy, it's theroy.
I'd still have to think the cooler the air and cooler the material you flow air through the better. It's not about volume, speed and rate of transfere.

It's really simple, is the air flowing through a 150 degree tube hotter or cooler then the air flowing through a 80 degree tube?

It's not so much about over HP, as the C&L and JLT have been proven to be within 2 HP of each other. What the thread is about is how hot the aluminum gets.

Let's look at it another way. Consistancy at the track.
If you want consistancy you need to keep inlet temps consistant. As aluminum gets hotter it IS heat soaking the air sitting inside it in the staging lanes and the pits. It will take some time for the cooler air to flow into the engine compartment and cool the MAF signal to tell the computer to bring timing back up.

Same situation, but the tube is plastic and much cooler. Less heat soak and less timing is being pulled and less time to get the timing back to normal or what the tune was set for.
Now I know were talking about a very short time and splitting hairs, but if there's an argument that aluminum is not as bad as you think, then there's a argument that the cooler you start off with the better as well.

Interesting,

Jay

mikeelia

Well, for what little it is worth I put that Summit self-stick aluminized heat wrap on the bottom and sides of my WMS ram-air plate. The manufacturer didn't think it would be needed either, but I spend [too much] time sitting in traffic, so I figured for a few bucks it couldn't hurt. Hey, it makes me FEEL better! LOL

Mike E

gambi06

I remember one of the other guys (I think it was Kooldawg, on another forum) saying that he had to order a replacement ram-air plate for his WMS, due to heat warpage, so there's a side-benefit of keeping it cool!

Anyway, back to the cool vs. hot issue: There seems to be good points made from both sides of the fence on this one, and I guess I feel like, if there IS any good to be had by keeping the intake tract cool, it certainly isn't HURTING to do so, so I'm going to err on the side of caution, and keep it cool. If it doesn't have any effect on performance (which ironically, I won't be able to determine in this 103 degree heat!!), then it'll be no-harm, no-foul, in my book.
Again, my solution isn't pretty to look at, but I don't pop my hood either, so...

RedDragon777

This is what i want to see, some one stick a thermo sensor in the silicone connectors, before the MAF (in the filter) and before the TB and do this for a C&L racer and a JLT intake and see which one runs cooler under WOT for a few runs down the track

65sohc

I did a similar experiment several years ago on a 94 single turbo Supra with 522 rwhp@17psi boost. I was running an AEM progammable ECU. Between the intercooler and the throttlebody was about 2 feet of aluminum tubing. (This was a speed density system. Hence no MAF.) I first placed a temp sensor a couple inches in front of the throttlebody. During idle the temp reading would skyrocket, though I don't recall the actual numbers. Next I tried mounting the temp sensor at the intercooler outlet. To my surprise the readings were identical to those in my first test. At idle the temp shot up but as soon as the car started moving and the RPM/airflow increased temp dropped to near ambient. Finally, because the piping became too hot to touch at idle I tried wrapping it with some Thermotech reflective insulation. Again the results were exactly the same as before. I'll also add that IAT at WOT and 17 psi@6500 rpm was within 5 degrees of ambient. A very efficient intercooler.

ski

There you have it. Test results that prove the theory.
Actually, I already knew the results, since I had participated in a similar test in a heat transfer lab while attending college(a long time ago, in a galaxy far, far away).

kevinb120

Everybody thinks that when high-flowing outer air gets in a hot tube it instantly gets hot Its flows through it in milliseconds.