Intake drawing air through intercooler -- good, bad?

That's the setup that ATI uses on their Procharger setups for 4th-gen F-bodies.  As was the intercooling setup on the system someone (LPE?) designed for that same chassis.

It works in practice because the air moving through the intercooler doesn't pick up very much heat.  Much more air is passing through the outside of the intercooler, mass flow wise, than is going through the inside.  This makes sense if you put a little thought to it, because if you're cooling 200 degree air to within 10-20 degrees of ambient, the outside air passing through it has to be by definition picking up less than 10-20 degrees, otherwise heat transfer wouldn't be happening.

EDIT: It took me so long to be wrong that a better answer was posted *before* mine! I can't help but remain dubious, but apparently it works?

For the effort involved in creating enough of a duct to make the intake actually draw air through the intercooler fins, I'd say just make up a little duct to get a tiny bit of air from up front back to the IC. While I get the mass/delay thing, I think a system that guarantees that 100% of the heat being removed by the IC is being added to next air that's going to enter the IC can be improved upon.

Ten cereal boxes telescoped together from the front end and duct-taped to the IC would do *something*.

I suspect you'll be in some amount of boost pushing that brick down the freeway. Pull a hill at freeway speeds, and you're going to be preheating your intake charge pretty quickly.

I am sooooo far from a turbo expert. If there are contradicting answers from people with more practical experience, disregard me. But that truck with the 240 is, I'm certain, no rocket ship, and I'm pretty sure "on boost" isn't going to be a WOT-or-near thing.

In reply to Knurled. :

I think I'm having one of two misunderstandings: Either it's pretty much as in the picture, in which case I'd suspect it would have little impact on actually moving air through the IC (if this is where I'm wrong, how does that work?), or an airbox would be added so that all air was drawn through the IC, in which case the cooling air and the cooled are are exactly the same mass...

Ransom said:

In reply to Knurled. :

I think I'm having one of two misunderstandings: Either it's pretty much as in the picture, in which case I'd suspect it would have little impact on actually moving air through the IC (if this is where I'm wrong, how does that work?), or an airbox would be added so that all air was drawn through the IC, in which case the cooling air and the cooled are are exactly the same mass...

The turbo might be pulling in 500-600cfm of air at peak horsepower (far less at less than peak HP, obviously), but there will be several THOUSAND cfm of air going through the intercooler at speed.  That is the key difference.  There is also a decent amount of heat lag involved, for the first few seconds of boost the intercooler acts more as a heat sink than a heat transfer device.

You do have a point, that with as much undercar real estate as there is, it should not be difficult to give the air inlet a separate duct.  Ducting is going to be required no matter what to ensure airflow through the intercooler, although it could probably be as simple as a 3 sided box on the top and bottom.

In reply to Knurled. :

My impression was that he was specifically using the intake to draw air past the IC fins, and for that to be a meaningful contribution to moving the air, it would have to be a meaningful contribution to the total mass of air. It's one thing to have the intake drawing air that's been through the IC, but something else to be using the intake to draw air past the IC.

I'm now unclear on whether he simply means to have the intake near/above as in the picture, which I don't see a problem with (apart from the fact that the IC is really, as noted, not going to be getting significant airflow), or whether he intends to duct it so that it's really moving air past the IC, but is then drawing all its intake air past the IC before putting it *through* the IC.

I think the latter may be entirely my misunderstanding, but the phrase "drawing air through the intercooler fins" from the first sentence then doesn't really fit. It'll be near the IC, but I wouldn't think that much of the air it'll be ingesting will actually have traveled through the IC...

jamesl, which mistake(s) am I making? 

EDIT: to address one of Knurled's specific points, I don't think there's going to be thousands of CFM passing through that IC in its current configuration installed horizontally under the truck.

Sorry for any confusion. I did plan to have a small scoop below the intercooler and a box around the intake and intercooler. My concern is the small scoop wouldn't direct enough air through the intercooler by itself, but the sucking force of the intake above the IC would help increase flow through the IC fins. I get the point about the brick-like nature of the Econoline and do suspect I could see modest boost at highway speeds.

It would be awkward, but not impossible, to build a ducting system to bring air back to the IC. Maybe something a little better than cereal boxes. . The Intake/IC assembly is directly behind the passenger side front wheel (just outside the picture), so it's not a straight shot forward to the front of the truck.

In reply to jamesl :

The airflow going into the turbo is very minor compared to the airflow requirements of any air heat exchanger.  Air simply isn't all that great at transferring heat.

A good airdam behind and under that intercooler, and a dam on top in front, with fencing on either side, would do a pretty durn good job of forcing air through it.

This is admittedly one of those applications where water-air would be awesome.  You can stick the intercooler anywhere that makes the air plumbing easy, then stick a big ol' heat exchanger up front.

In reply to Knurled. :

I'm going to try the air dam system and see how it works. I can always redo later if my temps seem to high.

This is admittedly one of those applications where water-air would be awesome.

I actually installed a water/air IC system on a 1st gen MR2 I turbocharged many years ago. Worked great but a little more complex than what I want with this project. Fond memories of a car long gone!

It'll work fine but it's not ideal. If you can't get the air filter itself out in the front of the car, you could make a shroud/housing for it and have fresh air pipes from the front leading into it.

Looking at your pic, why not just extend the intake piping up and over the IC, and then have the air filter in front of the IC. Boom, no worries about warm air from the IC.

However, I'm also worried about what puddles and dust are going to do to that poor air filter under the car. You should either use longer intake piping to get the air filter into a more traditional, splashproof location, or have an enclosed air filter housing with sealed piping running to the leading edge of the car, as high up as practical.

Edit: If you want more airflow through the IC, duct it, or go air-to-water with a separate radiator.

I goofed up. I deleted the first post, thinking it would delete the entire thread. Apparently not. Thanks for all the advice everyone. I'm going to reconfigure things and come at it from a different angle.