John..

As my new 928 turbo project gets underway, I thought I would run some ideas on intercooling here on the list, so here it goes:

Air to Air front mounted:

Positives: Simple, Reliable, looks great, allows stock air filter to be used, typically more efficient if sized properly.
Negatives: Longer pipe runs, potential flow restrictions if not sized properly

Air to Water top mounted:

Positives: Shorter pipe runs, potential larger flow area
Negatives: Much more complex, more costly, heavier, requires aftermarket air cleaner, potentially less efficient at steady state full tilt conditions


My gut tells me air to air is the best way to go for simplicity and all around performance. I can't deny the temptation to consider air to water, however I don't see these being used on most race prepped cars and it seems very complex in the grand scheme of things and somewhat of an afterthought. Air to Air is always used by Porsche and Audi. With that said, these air to liquid units are showing up on some of the new production cars, Ford GT and MB supercharged models. I know the early 928 cars have enough room for an air to air big enough to support nearly 500 HP, which is more than enough space. I am trying to keep one of the goals of keeping the top side of the engine looking basically stock. Stealth is a great way to go if you can swing it.

Opinions, preferences?

bcdavis

Only if you have a system for low water warning, or something like that.

Otherwise, as the years go on, and someone is not diligent,
and they have a leak, or evaporation, and the next thing
you know, detonation, etc...

Air to air is a lot more "idiot-proof".

John..

Now, if they can only put an idiot proof nozzle on the gas filler that won't allow 87 octane to be put into the tank...

Lagavulin

There is no arguing that air-to-air is recognized as the best solution, space permitting.

Old & New

When the windshield washer reservoir doubles as your holding tank, then you have a low fluid level built right in.


John,

As long as the intercooler radiator is sized properly, there is no reason that the system would be less efficient at steady state conditions. Consider if you are building a street car or a track car.

I agree w/ bc in that air-air is more idiotproof, and would recommend an inlet air high temperature alarm for air-fluid systems. This is on my to-do list.

I think the greatest appeal of air-fluid systems is their small size and simple air plumbing requirements.

FWIW, I don't think the air-fluid systems are all that much more complex, costly or heavy.

mspiegle

i like the idea of having less piping. Pipes are evil.

2V4V

Lag,

There's plenty of aguing that.

Just to throw out a coupla other things - as John enumerated, either scenario has it's +/- equation.

Thermodynamic efficiency does not go unchallenged to the air to air. In fact, most guys who do this stuff for a living will tell you the opposite (though 5 or 8 years ago, things were different). And if you f-up the design (size, route, location, clamps,velocity,etc), either one will be lousy at best. Half the homebrew stuff I've seen has been a joke, albeit a bad one. This is not to say that it can't be done right (either scenario) one must just pick up one of them thar' book things and do some readin'. The knowledge is pretty simple, but if you don't have it, there are some easy traps to fall into - I've seen tuners commit some of them, like doubling the length of an air to air instead of splitting and paralleling. Kinda sounds like it would work, but it's bad for a whole host of reasons.

Race teams use air to air for the sake of simplicity and lightness. (There is something to be said for those ideals. What was the Mark Twain quote about JF Cooper's work, "Simplicate, add lightness.", IIRC...

There is a weight penalty for water to air, and the hardware is a skosh more complicated - one (ok, like 5 or 6) more thing(s) to go wrong.

But they do not use air to air because it is more thermodynamically efficient than air to water.

Greg

Garth S

Air - air on Audi quattros is sooo trouble free and invisible .... and no moving parts to service! Yes to air - air.

Old & New

Back to weight difference...

My air-fluid intercooler weighs what? Ten pounds? The associated radiator weighs maybe five, add another five pounds for fluid pump and rubber hose. The windshield washer fluid was there already.

(Tim, Lag, Gretch, please correct me on these numbers; it has been a while since I did the install)

How much less than 20-25 lbs. is an air-air I/C and plumbing going to weigh? What if the air-fluid setup weighs 10 lbs. more? Does it matter?

No offence, Greg, just my opinion.

John..

Assuming the heat transfer areas are adequate, I do believe the air to water suffers because of the two step heat transfer process....i.e. n(tot)=n1*n2*n3.....but it does have the clear advantage when it comes to size and size does matter... At some point steady state will occur and you can only dump so much heat before the limitations are reached. For a street car, this may not be that big a deal lending merit to the air to water.

My core now is 3.5" x 18" x 6" and flows out real nice, but it was a tight squeeze. Thanks to Bell Intercoolers for the fabrication of my complex design to fit Callaway's existing plumbing. It uses a 6-way split on the inlet feeder to distribute across the core. What always amazed me is how the OEMs and some tuners flow from left to right when a top to bottom has a much greater flow area and the same heat transfer area.

It really is a complex design effort given the space constraints. Thank goodness for styrofaom models.

John..

10 lbs would not matter, heck I could afford to lose 5 lbs myself.

Gretch

Some information: the windshield washer has a capacity of 2 gallons. you add another gallon to the overall capacity when you install the radiator and AWIC. Water weighs prox 6 pounds a gallon.....I bet the whole contraption prolly weighs 10 pounds plus or minus......

Old & New

John..,

Anecdotally, I have done my share of racing around and often checked the temperature of the I/C outlet (air temp) and radiator fittings (fluid temp). I have always found them to be at ambient.

2V4V

Old&New/Gretch,

No offense taken, just trying to maintain some sort of impartial recounting of the current state of the shelf.

I personally prefer water-to-air, if done properly, it is more efficent, which works out to be more beneficial in a HP/LB equation compared to air-to-air, even with the added weight.

To be fair, how much weight is added (A/W v. A/A) depends alot on how long you need to shed heat from boost.

One can make a case for either setup, just depends on what your needs/wants/budget dictate.

Greg

John..

Greg,

I disagree that it is more efficient. Perhaps for an instant, but at steady state I don't think it is more efficient, unless you are on a lake in a boat. However, as you state both technologies have merit. I am just evaluating which one to use as I effectively have a clean sheet of paper to start with and that is a nice feeling.