Intercooler: What is it? What does it do? How does it do it?
 

I had a vague notion of what it does. So I Googled for some info and found this site which offers a pretty good explanation. Hope it helps you, it worked for me.

Bot


http://www.gnttype.org/techarea/turbo/intercooler.html

You located just about the most informative site out there for turbocharged vehicles.

I didn't check the site, but my simple mind is under the impression that cooler air is denser with more o2 molecules hence more 'oomph'.

It took a lot of math and graphs to explain that to me. Now I finally got it.

It really is a detailed look at the why and how of it all.

You aeroplane guys, is that why fancy-schmancy fighter jets squirt water to boost speed? Somebody told me that one time and I thought he was FOS. Maybe not?

B

Some engines squirt water into the intake, older Corvettes could be set up for this due to the fact high octane gas is no longer available. I never heard of a turbo squirting water. There are however, water to air intercoolers in addition to the normal air to air type. To go full hog, use an a/c evaporator coil in your intercooler setup (with the a/c working of course)

Here's an account of a conversion of a Travco 440 to a Cummins turbodiesel. Instead of a 'traditional' intercooler, he snaked 22' of tubing under the front bumper where the air would flow over it. I'm inclined to think that the reduction in temperature of the air would not be that significant with that setup. Other opinions? I'd be inclined to think that an intercooler like Z's would be much more effective.

http://community.webshots.com/album/232660691ZBdqUT/4

I always thought that the reason intercooled engines had better performance is that cool air takes less energy to compress than does hot air. An intercooled engine, therefore, consumes less energy on the compression stroke. I'm pretty sure that is why multi-stage air compressors benefit from intercoolers between stages.

Colder air makes more power since there are more molecules of oxygen in a smaller space. In laymans terms, it makes a bigger boom when mixed with fuel and spark so more power is made. I'm running 50% methanol & 50% water mix as well as an air to air intercooler on my SEC to prevent detonation and to further cool the intake charge.

I belive the Subaru STI has a air to air intercooler that has a water mister device that cools down the intercooler a few degrees when it's hot out or you're really into the loud pedal. I am curious to know it's effectiveness. My WRX had a small hood mounted intercooler which was apparently efficient enough to squeeze 113.5hp per liter out of that motor. :)

Intercoolers are very common on forced induction engines for two reasons: it gives more power/efficiency as earlier explained, and it prevents detonation as the charging increases the temp of the air/fuel mixture going into the cylinders, which the IC cools. Running a turbo without an intercooler will very likely melt down the pistons.

One of the guys over on the diesel section was talking about fabricating an inter cooler for the 617 several months back. I forget his name but I think he was the fellow who wrote the good piece on putting a 2.43 rear end from an SEL into the back end of a 300D with a 3.05 rear (numbers close).

Here is some technical background about intercoolers. When you compress air or any gas for that matter it heats. There are relationships in classical thermodynamics that mathematically describe this. The one that comes to mind is the isentropic compression. If you compress air from 14.7 psia to 29.4 psia, the temperature would rise from 70 F to 186 F. You cannot let 186 F air go into your engine because it will cause the engine to knock. So you cool it through a heat exchanger. The cooling also increases the density of the charge allowing more oxygen to enter the engine and hence more power to be developed. The intercooler is an air to air heat exchanger.

Expressed mathematically, the relationship is

t2 = t1 * (p2/p1) ** 0.286

where t2 is the final temperature, t1 is the initial temperature expressed in degrees Rankine.

p2/p1 is the pressure ratio of absolute pressure

0.286 is a constant derived from the ratios of specific heat of air which happens to be 1.4. The ratio is the specific heat for constant pressure divided by the specific heat for constant volume.

So at 70 F which is 530 Rankine and a 2/1 absolute compression

t2 = 530 * (2) ** 0.286 = 646

Expressed in Fahrenheit degrees, t2 = 646 - 460 = 186 F

Note that if you use 100 F ambient air, you would get

t2 = 560 * (2) ** 0.286 = 683

t2 = 683 - 460 = 223 F

So a 30 F rise in ambient temperature causes a 37 F rise in pre intercooler temperature.

Damn, I knew I shouldn't have dropped that thermodynamics class. One thing that puzzles me, and I have no idea how to pursue an answer for this, is:

If you deposited a cylinder full of air in a 617 and it was say, twice normal atmospheric pressure but had been cooled down to ambient temperature -- would that quantity of air yield the same or greater temperature after being compressed by a merciless piston as would a cylinder full of air at the same temp but at normal atmospheric pressure?

I want to say it would be a greater temperature because the increased density of air molecules in the first case would cause a greater increase in temp than the more sparse concentration of air which is, nonetheless, perfectly good for breathing.

The change in absolute pressure in the case of a standard 617 is 21:1. The air is compressed to a volume that is 1/21 of the original volume. The temperature goes up accordingly.

In the case of this hypothetical 617, the change in absolute pressure is the same 21:1. The final pressure in the cylinder would be 609 psi, which would have blown the head right off the engine. However, if it remained intact, the change in pressure remains at 21:1. So, the temperature rise would be the same as the standard 617 if they both started at the same temperature.

I always thought it had to with an inter-office waterfountain....whodda thunk?