John..

Here is an interesting article on air-air vs. air to water charge cooling.

http://www.panhandleperformance.com/intercooler.html

Why not go all out and design a system yourself?....Centrifugal blower, then design the plumbing for a healthy air to air charge cooler, back to the the throttle body. Space it tight up front, but I have been able to fit a core large enough for my air requirements with room to spare. My core can support 450 HP, maybe 500 in a pinch. There is some more space left so a 600 HP air-air could probably be made to fit without too much trouble. A real trick twin turbo setup would be to put the charge air coolers up under the headlights...lots of work and cutting, but I'd bet it can be done.

I want to see someone keep the stock air intake system and just route plumbing to get to the centrifugal blower and back to the throttle body....that would be trick, but maybe not possible on the S4?. I've never been a fan of the cone filters people use these days...but they are easy to setup and have functioning.

We'll never agree on SC vs Turbo, so I won't bring it up again...anyway take a look at the article it is really well put together.

BC

HOnestly, the air to water system is just too easy on the 928, and the air to air too hard. Whats more, I can place the weight in better positions, or even in positions as I see fit (i.e., the tank in the rear area)

I can also place the system radiator for the inercooler in a different location so as to not inhibit the flow into the AC and main radiators.

I cam currently trying to get the car on the road after a year (it will be more than that soon) - With a DTA install and motor rebuild, I need to get these thyinsg done before I can think about shelling out more cash for 650hp. It will happen, but I need to compartmentalize here.

Did you leave the cradle on the block when you sent it out for nikasil? It needs that cradle on for boring - even more so - the head torquing needs to be sythesized with a block plate.

John..

Yes, the girdle went out with the block for sure....just make sure you don't damage or lose it...they are line bored together. They use the lower surface as the datum for machining the bores. I built a crate for $20.00....UPS sent it up, but the UPS guy on the way back would not deliver..."it is too heavy"...it was $175 lbs., their limit is 150 lbs.

Agreed on the plumbing, but I still think it would be a sweet setup...

BC

I am having the engine bored HERE. The girdle will not be sent with the engine block to Wisconsin.

GoRideSno

OK Lagavulin,
Here are a few for you:

#1
10.5:1 CR
.9 bar
Twinscrew compressor
Air to Water IC (rate it's efficency as you will, please specify)


#2
10.5:1 CR
6psi
Twinscrew compressor
no IC

#3
10.1:1 CR
6psi
Centrifugal
No IC and ambient air temp of 180 instead of 90 (I would assume one would use 640 instead of 550 in their calculations)

#4
10.5:1 CR
5.5PSI
Roots
No IC

#5
10:1 CR
8psi
centrifugal
No IC





Andy K

Lagavulin

You didn’t specify what you wanted, hp numbers or combustion chamber temps, so I’ll do both.

The derived numbers utilized the following calcs: pressure ratio, density ratio, volumetric efficiency ratio, drive power efficiency, ideal temp gain, thermal efficiencies, real temp gain, heat made by supercharger, heat made by supercharger and compression ratio, and heat made by intercooled supercharger and compression ratio.

All calcs are from Corky Bell's 'Supercharged'.

IC efficiency: 85%
Twin-Screw Thermal Efficiency: 70%
14.7 psi x .9 Bar = 13.23 psi
Compression Crank HP Adjustment = 316 x 1.02 = 322.3
Combustion chamber temp: 1107.24 degrees absolute
Crank hp: 552.86

Twin-Screw Thermal Efficiency: 70%
Compression Crank HP Adjustment = 316 x 1.02 = 322.3
Combustion chamber temp: 1215.08 degrees absolute
Crank hp: 373.38

Centrifugal Thermal Efficiency: 75%
Compression Crank HP Adjustment = 316 x 1.004 = 317.3
Combustion chamber temp: 1386.90 degrees absolute
Crank hp: 402.93

ps. Yes, you are correct. But I used 180 ambient and added it to 460 which of couse is the same result as you've stated, 640.

Roots Thermal Efficiency: 55%
Compression Crank HP Adjustment = 316 x 1.02 = 322.3
Combustion chamber temp: 1242.21 degrees absolute
Crank hp: 356.41

Centrifugal Thermal Efficiency: 75%
Compression Crank HP Adjustment = 316 x 1.0 = 316
Combustion chamber temp: 1228.78 degrees absolute
Crank hp: 425.64

Carlos

Panhandle Performance is a Mustang oriented operation. Trust me guys, the American car guys are way, way ahead on s/c technology. And as far as tuning a blower or turbo application, I would trust Panhandle, Wayne Young, Murrillo Mororsports, Steve Petty, the Spetters or any of the V8 specialists to do a good, safe job of tuning without any attempts to rape your wallet. Anybody who tells you this stuff is black magic & costs a fortune is either a thief, a liar, uninformed or a combination of those three. We can learn a lot from those guys.

John..

I threw the intercooler article in to clarify the differences between air to air and air to water charge cooling. Both have merit in differing situations but air to air is the definite way to go for a street car (if you have the room).

The panhandle article is a good one. I passed it along to my friend with the Mustang that just smashed two pistons up as a result of detonation...he will be charge cooling his car for sure now....that is after he puts a better bottom end in it.

GoRideSno

Thanks,
Now I can check my math against yours.
Sorry, I should have mentioned just combustion chamber temps. Since most of these are not 928s I think we would need more info to get correct HP figures, good reading though.

Behind door #1 2003 Mercedes CL55 AMG

#2 Whipple industries Cadilac Escalade SC system

#3 I had meant to represent the FAST 928 system as described HERE . I should have used 5 psi though. Since Mark R specifies a 100 degree day I guess we could actually use 650, assuming underhood temps are 90 above ambient. So the new equation is 10.1:1 CR, 5psi, No IC, 190 degrees ambient. Really scarry when you conside rthe 85-86 has no knock sensors.

#4 Lingenfelter Z06 Eaton SC kit, over 500hp.

#5 928S4. Has anyone run an S4 at 8psi and no intercooler? I thought I read that someone had done it for a whole year.


Andy K

Old & New

John..

Smashed pistons due to detonation? So much for the Mustang guys being way, way ahead...

I'm not as impressed as you with that Panhandle info. Consider the source... they manufacture air-air intercoolers. How do they figure that air-water units only yield "35-65% hp gains" when they claim "25-45% hp gains without intercooling"? Heck, Tim and Lag are running over 85% more hp than stock... The vague references to "others" and "some companies" in their sales pitch doesn't lend much validation to their claims.

Also, their other claims are either outdated or just bunk. No ignition retard on my system... "Inherently inefficient"? "Afterthought"??? And it certainly isn't any more difficult to install than running huge plumbing all over the engine compartment and inside the nose.

I consider air-water an elegant, tidy way of intercooling an already cluttered engine compartment.

Z

The information on the Panhandle site is directly from ATI, who manufactures air-air intercoolers, and who's products Panhandle sells.

In the small print at the bottom of page 2 of that information it states:
"Centrifugal supercharger system on EFI motor in street use; Performance of air-to-air intercooled system can be matched by air-to-water intercooling on some application, but only with the frequent addition of ice to water/ice tank."

Tim had talked to the ATI guys in the past. Apparently they seem to think that everyone with an air-water system is using a small water reservoir, and an inadequate radiator for it.

2V4V

The other of many downsides of air-to-air is loss of charge velocity and pressure, and added time for "spool-up" especially as you get into the larger HP numbers, which need bigger charge coolers. Imagine a few 951 intercoolers welded together and you'll get the picture.

This, coupled with a distinct shortage of clean air for a massive a-to-a, makes it a tough sell, on a 928 anyway. That it also requires massive plumbing moving through an already cramped engine bay makes it a real challenge to do. Hardly imposible mind you, but if you put an air-to-air in front of the a/c condenser and the radiator, how long before the radiator starts losing efficiency (let alone the a/c)?

But you have lotsa places to stick 1, 2, or 3 air to water rads throughout the front airstream, with minimal/no impact on engine cooling air.

In it's favor, it's about as mechanically simple a device as you can have, and it has no pumps to fail, or fluid levels to occaisionally monitor. And (IF) you find someplace to put it, it can be easier to get it effective for longer periods of boost before it heat soaks to the point of no return.

There's an argument either way, just depends on what your needs/goals are.

Greg

John..

When sized properly air to air will always win, that is a fact. Talk to the guys at Bell Intercooling or check out their website...they know as much as anybody about charge air cooling.

A charge cooler doesn't have to be huge to work well...mine is just 3.5" x 6" x 18" and that is big enough for 450+ ponies.

Old & New

John..

That qualifier ("properly sized") can be applied to the design of either system. As long as the convective surface areas are adequate to absorb and dispel the heat, where is the thermodynamic disadvantage to using an air-water system?


I may be way out of my league by disagreeing with the info on Corky’s site, but he says:

“…the water intercooler largely stores the heat in the water until off throttle allows a reverse exchange.”

This suggests that the water intercooler system is not dispelling heat while absorbing it. Actually, both transfers occur simultaneously and continuously.


It is also stated,

“Some heat is expelled from a front water cooler, but the temperature difference between the water and ambient air is not large enough to drive out much heat.”

A small temperature difference between the water and ambient is what we want! I observe this in my car. The temperature of the circulating fluid remains nearly at ambient temperature even after spirited driving. Apparently the heat absorbed by the intercooler core is readily being shed by the “front water cooler”.


He relates the movement of heat across the exchangers as a bottleneck in the charge cooling process:

“Another way to view the situation is that ultimately the heat removed from the air charge must go into the atmosphere regardless of whether it's from an air intercooler or a water based intercooler. The problem with the water intercooler is that the heat has more barriers to cross to reach the atmosphere than the air intercooler. Like it or not, each barrier represents a resistance to the transfer of heat. The net result; more barriers, less heat transfer.”

I am sure there must be circumstances where this applies (maybe an undersized “front water cooler”?), but I believe this would be better addressed by one of our resident thermodynamic engineers. It strikes me as just a question of the efficiency of the exchangers. If the exchanger which sheds the heat is sized large enough, it won't bottleneck the heat transfer.


It’s not that I am criticizing air-air systems; but they have a few pros & cons, too:

“At just 60 mph, with a 300 bhp engine at full tilt, the ambient air available to cool the intercooler is about ten times the amount of charge air needed to make the 300 hp.”

How about at zero mph? An air-water system operates at full efficiency right off the line.


Curious, does Bell sell both types of intercooler, or just air-air systems?

John..

The total system efficiency can not be greater than either of the individual heat exchanger efficiencies....at steady state conditions.

I think the point Corky makes is that during transient warm up, the water can take on huge amounts of heat. It then has to shed this heat through a second intercooler. So, if you have lots of cold water in there, it will cool tremendously, until the water reaches higher temps....then the second exchanger has to dump the heat.

So full tilt, steady state the water temp will rise and the only amount of heat you can dump then becomes totally dependent on the efficiency of the second heat exchanger. The system's total efficiency becomes a function of the efficiency of both heat exchangers. Provided your boost is used on occassion, then it will work well (water to water), but long durations steady state you reach the same conclusion every time. Sizing of the second exchanger should probably be based on the amount of time you want to run boost. Bigger for longer boosted periods.

The zero MPH rule is silly, no car makes boost at zero MPH. The air to air does have capacity to store boost heat in the aluminum itself...it is a huge heat sink, especially a bar and plate style core. On the dyno, the air to water will win assuming the water is cool enough. Most cars will be travelling 30 MPH before any significant boost comes in.

I believe Bell makes both styles, I am sure they do offshore racing boat cores of the air to water style.

Too bad these sharks can't swim becasue the true air to water unit in a lake or ocean can be over 100% efficient....wouldn't that be nice?