Warning – sarcastic content –

If you take the core out and replace it with a one large square tube then you will really increase the flow….is that what you really want?

There is an interesting balance going on in an intercooler – on one hand you want as much contact time as possible to transfer the heat, on the other hand you don’t want restrict the flow.

BTW – if you consider that the intercooler was designed for 250hp max then the engineers at Porsche did a fine job – no need to maximize it any further. The mind set at Porsche in the 80’s was that turbos (944 or 911) did not need the intakes ‘maximized’ because they were force fed. If there was some restriction you could just run a little more boost at the turbo output to reach the desired pressure in the end of the intake tract. Just look at the 930 manifolds…(ugh!)

Chris White

 

Of course you're right about water and air density. OTOH, the reason that I suggested the simple & cheap water flow test is that various aerodynamicists (Hoerner, Carmichael, Jones, et al) who've published works (copies in my library) have all said that water flow and air flow are sufficiently similar for most subsonic tests. In other words, a flow test done in a water tank indicates pretty much the same as one done in a wind tunnel.

Here's another simple & cheap suggestion: Get some infa-red 35mm film and shoot before and after pics of the IC, to see where it's hot and not. Or, use one of those infared sensors that some car shops use, with digital readout. Or, maybe one of those plastic strip thermometers would work.

Seems to me, we want the smallest possible IC (less plenum volume and therefore turbo lag) extracting the greatest possible heat from the internal flow. Tiny little channels through the IC expose the internal flow to more surface area (the good news), but make for too much internal restrictive drag and resistance (the bad news).

Here's a few more thoughts, just for discussion: 1). Consider using copper for the IC and associated plumbing, because copper conducts heat TWICE as well as aluminum; 2.) Add proper ducting for the ambient cooling air, such as a cowl flap, and; 3.) add mini-fairings to the external IC channels, to assist ambient flow through the IC. In stock configuration, the ambient cooling air runs into a flat surface and lots of tiny little sharp angles, which restricts ambient through-flow.

 

The plenum and pipe/IC volume has nothing to do with lag...unless it's too small and restrictive for the application. Chris said it right,the stock IC is made for 280-or-so hp peak. Want more power,make a core that flows more. Then get bigger piping. After that,then change the design of the end tank. I've flowed several aftermarket design end tanks through a 951 core,not a single one gave higher CFM. That "might" have something to do with the fact that the "narrow" section in the stock end tank still has a bigger area than the IC piping... That "narrow band" also happens to be more efficient than a huge tank in turning the air flow into the core.

 

I think sh944 is correct. The reason for the tapered end tanks is to create pressure drop. The end tanks were designed the way they were because they wanted to drop temps with restriction rather than surface area.
There are two ways to cool air. Restriction or increased surface area. Both will give you pressure drop. Without pressure drop there is no cooling effect. (SCIENTIFIC FACT)
Increased surface area has a drawback. It takes up space. The larger area will also drop pressure because temps are reduced. So even if you were to use a large IC you will always have pressure drop or else your not cooling the air. Porsche uses both techniques to cool the charged air witch is fine. The reason I think they went this route is because of the limited space they had. Opening the end tanks will more than likely not cool the charged air that well. That means detonation will be present at lower boost. This is one restriction in the intake track I wouldn't free up unless it's traded for surface area.

 

Where is our pictures

 

"There are two ways to cool air. Restriction or increased surface area. Both will give you pressure drop. Without pressure drop there is no cooling effect. (SCIENTIFIC FACT)" So, Jimbo 111, you are saying that restriction will give a pressure drop. You are right, it WILL give a pressure drop... on the downstream (engine) side of the restriction. Restrict the flow, and reduce the volume.

As for the concave-tapered end cap at the front side of the IC: Why would the heated and pressurized turbine air not just take the path of least resistance, and go through the less-restrictive middle section of the IC, which is a shorter, more direct path with less bends? Unfortunately, the middle section of the IC does not get too much through-flow of cooling ambient air, and/or said cooling air is already somewhat pre-heated by the time it gets to the middle, so doesn't cool so well by that point. Your comments?

"The plenum and pipe/IC volume has nothing to do with lag." Skunk Works2, are you saying that a very large IC with a large internal volume would have no more lag than a small-volume IC? If so, this means a large volume of air has no more inertia to overcome than a small one. Please explain.

And, what do you gentlemen recommend for improving cooling efficiency of the stock IC?

 

Here are the pictures that Wolf Pack sent me:

 

To me the shape of the end tank looks a lot like a vacuum cleaner attachment. I always thought it was shaped that way for a reason, probably to encourage flow across the whole core. Naturally with an IC you are not just trying to flow a lot of air, you want it to spread out and use all the internal surface area.

-Joel.

 

Some of are on top of your game on this stuff and I by no way think I am smarter then some one with a college degree in this stuff or that I am smarter then the Geeks at Porsche. There has been post of flow cooling and the Bernilli effect and so on. We have talked about fluiddynamics of this and air and water having the same principles and on and on. I agree Porsche did this end cap for a reason if it was to de-tune the car so it did not over shadow the 911 or is ther was some other reason for it. Having cut open the IC and looking at other IC Porsche made, plus looking at IC from Spearco and talking to Turbonectics a Spearco dealer, I have yet to see a IC with an end cap like we have. We are also some 20 years after the design but I don't think flow and core temp design has changed any.

I am not running a stock car anymore I have a full LR 3" exhaust,15 lbs of boost, LR cone filter set up, 3 bar FPR and the LR dual port waste gate. So would you think I am pushing more air through the system? Doing these up grades is nothing but pure ole american Hot Rodding but with a German car. All of the aftermarket vendors are selling some kind of a inproved IC with 2 selling a moded end cap of the stock IC and up graded from the stock IC and a boat load of other stuff. LR might sell more then anybody and they sure seem to have allot of stuff and sell good stuff. They might be the top 951 dealer for after market parts. All Tab at Autobahn Garage and I are doing is trying something and seeing if it works we are going to put it on the duno and see if we have an increase in HP if it is even a slight amount say 5 hp then it might be worth doing. We will report our findings after we do this we are also going to be taking temp readings of the IC from the inlet and out let from the front of the IC and the back of the IC so that we can see if ther is a change for the better or the worse. We may find out that we are dumber then a box of rocks and that all that said it would not work were right and I will stand up and take my lashings like a man and move on saying nope it does not work.


Cliff 88 951

 

I'm not talking of inertia of air,because that's not the main contributor to lag. I've run dual-core IC's 30" wide,15" high and 6" thick ,with 3" tubing and enormous tanks on a car,then used 2.25" tubing and an IC less than half the size...and gotten LOTS of lag. The reason you get lag usually comes from trying to force more air than the IC/tubing likes through it,making an un-acceptable pressure difference between what the manifold sees and what the compressor has to deliver. When the compressor outlet sees 28-30 psi and the manifold sees 20 or so,then the restriction to flow out of the compressor gives you lag,it takes too much time to get through the restrictions and get the pressure to the manifold so the engine can "see" it,not to fill a tubing system that probably doesn't hold more than about 0.7 cubic feet of air at max,even when using 3" tubing...

BTW,the K26 moves 42.5 CFM at 3 psi at the very bottom of it's map...this means that it fills the entire volume of the 951 ducting and IC in about 0.3 seconds,given that there's no restrictions...and that's before it has started doing it's job at all.

Not much...it cools really well. What it needs is more internal flow,without loosing it's cooling ability of course.

 

Sure you are moving more air, but I doubt you are maxing out the intercooler. I have the same mods as you, altho I also have a MAF/Vitesse chip setup on my car. I am guessing the stock intercooler/hardpipes will flow enough air to support up to 400hp or so (BIG NOTE: This is all just speculation on my part, I've got no math behind this statement to back it up). That doesn't change the fact that I believe there ARE improvements to be had by doing some work with the intercooler. Any reduction in temp should increase hp, so its certainly worth looking at. I firmly believe that occasionally spraying the front of the intercooler down with a misting agent (water/alcohol mix would be my suggestion, but I'll let the chemists on the 'list lead this argument) would be more effective than changing the end caps. Moving to a larger intercooler in a different spot (ala SFR stage II intercooler) looks to be effective as well, given Tim's dyno sheet and the physics would bear that out (more surface area+ more flow= lower temps= more hp). Someone mentioned copper, which is a good idea except that it oxidizes badly and I suspect would have longevity issues.

Another subject that I will challenge "conventional list wisdom" on... venting the nose panel is a bad idea, even if you duct the opening directly to the intercooler. Porsche did some pretty neat (and advanced for the times) aero work on the 951, and cutting a hole in a low pressure area like that has all sorts of unintended consequences.

Regards,

 

Cliff,

Thank you very much for spending the time, trouble, and money to research this. I think you are on the right track and will anticipate that you will reap some benefit from this test. All of us can learn alot from your open-minded research.

As someone with a decent private library of books on fluid mechanics and experimental aircraft design (Experimental Aircraft Association member for decades, Air Force flight test background, and hobbyist), I recommend reading Dr. S.F. Hoerner's Fluid Dynamic Drag or various works by Bruce Carmichael, a leading aerodynamicist and sailplane guru who spent his life designing better jet fighter planes, navy torpedos, sailplanes, and faster racing planes. A good book on plumbing design is also handy, esp. basics of flow through pipes. Plumbers have some handy rules of thumb whch may be useful here.

I don't claim to be the big IC expert, but having read the life works of smart designers and fluid dynamics guys, have some serious doubts whether air flows very well through small nooks and crannies, or around acute angles and cracks like those in the IC end cap or internal passages.

Your pics are excellent, and show that both internal and ambient cooling air must flow past sharp angles, constrictions, and blunt shapes, which are far from optimum and more restrictive than necessary to get proper cooling exposure. The faster and more voluminous the flow, the more critical this becomes, as the drag increase is exponential: 2 X velocity = 8 X drag increase. At low flow rates, an improved IC won't make much if any difference, but as flow increases, drag increases very quickly.

 

All I ever thought was the feed end of the IC looked restricted, now looking at the photo with where I have the end cap cut off and next to the core it looks like to me that not allot of air could be getting to the front 1/3 of the IC. If we see that then I would think it would make more sence to open this up some and let air get through the core more evenly. I would think that this would let the air go through with less restruction and maybe we will get some better use of the front 1/3 of the IC and pick up some colder air and more HP. This is all I was after, by the way Dash 01 I am a plumber and own my own business.
Cliff
Wolf Pack 88 951

 

I noticed the ends inside too. Wouldn't these blunt/square ends impeed flow? Could someone weld/epoxy or otherwise attach semi-circular (half cylinders) to persude the air into the channels better???

Just a thought, if you are removing the end caps ayway.


something like this...

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951 North, those are my thoughts, EXACTLY.

I went to the hardware store, where they sell copper and alu. tubing in various diameters, including ~1/4", for cheap.

Seems to me, using brazing or hi temp silicone adhesive, you could add such tubes to the flat leading edges of the the IC bars, making a nice rounded leading edges for more streamlined flow.

Copper conducts heat twice as well as aluminum, so would be my choice unless bi-metal electric corrosion problems are an issue.

Brazing carries the risk of accidentally un-doing the factory braze job on the stock IC. If using silicone or other adhesive, you'd want to be absolutely sure none of the stuff could ever come loose and get swallowed by the engine.