Intercooler vs. No Intercooler

[Speedy Squirrel]

If you have the time and the inclination, Air/Water intercoolers beat air/air interoolers every time:

1. Water is has roughly 10 times the specific heat capacity of air.
2. The water flow can be controlled to the optimal flow rate at all times.

The above means that the engine mounted heat exchangers can be MUCH smaller than equivalent air to air units.

Because they don't have to "flattened out" like air/air units, their geometry can be better optimised for air flow, resulting in less pressure drop.

With an early 930 you could use the fender mounted oil cooler hardware from the later 930's to cool the water.

[polizei]

Originally Posted by spence88mph

Hey Andy, when you say 'rubber elbow' I asume you're referring to the Porsche OEM plastic elbow part? That's easily gotten deleted, I don't run it as mine kept popping off under boost, you just need to get a hose fitting somewhere in the intake path for the ICV and the brake booster, presently mine are tapped into the AFM but you could tap them anywhere.

Didn't know that that was plastic Would you mind posting a picture of how you're connecting to the intake to the throttle body? I just presumed that it would take 3-4 vertical inches to connect to the throttle body regardless of how you were doing it.

Originally Posted by spence88mph

you don't think it would be enough? You're crushing my next project plans! You don't think the above posted intercooler would be sufficient?

What are your intercooler plans currently? It seems like you already have most of it figured out and that it's not as much of an issue as I thought. I guess an additional 3" of cooling fins/tubes could make a notable difference in some cases, now that I think about it. On a front to back IC the longest cooling tubes/fins I could use is 5", so 3" would be a 60% increase. Not shabby!

Originally Posted by patkeefe

Ok, I'll chime in a bit. My water injection works very well, just as good if not better than air-air. If it's hot out, you can't get any approach on the condenser lower than ambient. My instrumentation suggests that it is hotter at the air inlet and past the throttle body than one would suspect. I can maintain under 120F temps at the track in the airbox, which is better than an air-to -air unit will get. I have shut the water injection off at the Glen as a test and saw 200F air in the airbox. The downside is a bit more maintenance (filling the water resorvoir counts as maintenance), and keeping the nozzle clean.

I did once speak to Gearhard at Bell, very sharp guy. I aslo spoke to the guys in Phoenix (Turbokraft, maybe), also very sharp guys. If I had to go air-to air, I would get the Phoenix guys to build me one. The biggest problem is the severe lack of room if you want to keep a no spoiler/wing/tray tail, although the 3.2 setup seems to bee a bit more roomy.

Pat

One nozzle, and a flow switch, all the rest is tucked away:

80 degree drop at the Glen? VERY impressive! I like this solution a lot because it doesn't add clutter or weight to the engine compartment, adds zero turbo lag, and it seems to be a less involved venture than a water to air IC. I've read that a lot of guys use windshield washer fluid. It's cheap and has up to 50% methanol for added effectiveness. When you're off the track, how many gallons of water/methanol do you go through on a tank of gas?

Pat, could you describe how you tapped into the windshield washer reservoir for this? How difficult it was? Any pics? Thanks!

[Flieger]

Originally Posted by Speedy Squirrel

If you have the time and the inclination, Air/Water intercoolers beat air/air interoolers every time:

1. Water is has roughly 10 times the specific heat capacity of air.
2. The water flow can be controlled to the optimal flow rate at all times.

The above means that the engine mounted heat exchangers can be MUCH smaller than equivalent air to air units.

Because they don't have to "flattened out" like air/air units, their geometry can be better optimised for air flow, resulting in less pressure drop.

With an early 930 you could use the fender mounted oil cooler hardware from the later 930's to cool the water.

Why did the Porsche factory prefer air>air intercoolers for the 935? They are better because the ambient air temperature is way less than hot water in a closed liquid cooling syatem. They only went to air>water when they were constrained in space and could not fit the air>air.

[patkeefe]

Although I am far from an expert, I am an instrumentation freak. I would completely agree with Craig on his points...short blasts on boost don't raise the temps much, and unless you are going to the track or hill climbing at a fast pace, most people can definitely get away with no intercooler.

Face it, if you are driving on the street, how long can you stay on boost before you are are on the dark side of road/traffic conditions? Then again, you have a turbo, you may as well use it.

Pat

[RarlyL8]

The problem you have on the street with air/air intercooling is heat soak. A non-ducted or incorrectly placed intercooler is probably worse than no intercooler at all. I assume that the point of this thread is to avoid that situation.
I also vote no intercooler. Try it out and get some data. You may be going through all this hooplah for nothing.

[Speedy Squirrel]

Hmmm, I think we have a disconnect here on the air/water intercooler concept. Porsche used it on the 934 because they were not allowed by the rules to change the "tea tray" spoiler to the whale tail. It uses a separate circuit of water to cool the air from the turbo compressor, and then rejects it to ambient with a front mounted radiator. It normally runs about 5 -7 C above ambient for water temp. In the Excellence I just received some German tuner applied the same concept to a Cayman Turbo conversion. Check it out.

I think the air/air system under discussion would be better for short bursts than nothing at all. If nothing else, it acts as a heat sink, as long as you give it time to cool down between bursts.

Problem is, what if you don't? A 930 at 0.8 bar boost is running around 110 C compressor outlet temps and flowing 0.25 Kg/s air. It doesn't take long to turn a poorly ducted air/air intercooler into a weenie roaster with repeated bursts. If you don't have ignition timing control with a MAT correction, you could have a real bad day under those conditions.

[Craig 930 RS]

"...how long can you stay on boost before you are are on the dark side of road/traffic conditions?"

Pat, exactly - that is exactly my basis for my no-IC post -

I can be on boost for maybe 5 seconds (7 seconds on an entrance ramp, up a steep grade) before people, license, car, & body becomes, um seriously endangered -


ANY track work at all absolutely requires an intercooler, 100%. Ducted, too -
~~~~~~~~~~~~~~~~

Brian, yes also very true - while sitting, the Intercooler easily EASILY becomes about 210+ degrees, and takes about 5 minutes of driving to cool off to an acceptable temperature.

The inlet/outlet Andial gauge is very useful in making these conclusions - highly recommended.

[Craig 930 RS]

I also experimented with the 5 second blasts at the maximum frequency I could do on a moderately traveled freeway.
Similar to negligent driving type stuff -

What I saw was the IC outlet temp increase about 4-5 degrees each time, lowering at slightly less than the rate of the increase - pretty close, actually.

Probably about 7 seconds to cool vs. 5 seconds to 'heat'.
(For a ducted RUF IC of modest size)

...also a 'big fan' of an IC with a fan...overlooked by so many folks with space constraints.

[A930Rocket]

As far as short bursts go, I wish I had the foresight last time I dynoed my car to bring some type of temp gauge/reader. I was amazed at the temp differential before and after a run.

At the start of the run, I had placed a bag of ice on the I/C. It was cold. With my hand on the I/C during one run, I had to remove it quickly, as the I/C had gotten so hot. Did it every time. It would have been nice to know the inlet and outlet temps.

I'm using a Kokeln BTW.

[patkeefe]

Say, I drive my SC and shut it off, maybe go into a store or something, deck lid closed. When I come back out to start the car, the ambient entering the air filter could be 30F over outside ambient, and the airbox could easily be +50F over outside ambient. Now, my induction system is different from a 930, and different from Andy's 3.2 setup, but these temps will all be somewhat similar in any air cooled engine venue. You basically have a 250F 300 pound block of aluminum and such sitting in a somewhat closed container. When the car starts moving again, it does cool off.

In my case, it was not effective to put in an air to air unit with the constraints I set. Thermodynamically speaking, it is aways better to have an IC. In my case, I felt the best bang for the buck, with these constraints, was to use the water injection system.

Did the factory even have intercoolers on the very early 930's?

[Flieger]

The 1974-1978 Turbo Carrera 3.0 liter had no intercooler.

1978 Turbo 3.3 liter with "tea tray" rear deck (opposed to "whale tail") did use an intercooler.

[Craig 930 RS]

IC temps indeed climb on the dyno, but for me at least appreciably so ONLY if the engine lid is open (which it usually has to be)

We now run her only with the lid open and a honking fan bungeed to the IC.
IC outlet temps never went beyond 83 degrees the entire set of 4 runs.
It is 100% about "air through the IC", in a functional and true way -

Honking fan:
http://home.comcast.net/~craigcarolann/trackvideos/930_November_11_2006_dyno_009.mpg

[polizei]

Originally Posted by RarlyL8

The problem you have on the street with air/air intercooling is heat soak. A non-ducted or incorrectly placed intercooler is probably worse than no intercooler at all. I assume that the point of this thread is to avoid that situation.
I also vote no intercooler. Try it out and get some data. You may be going through all this hooplah for nothing.

Thank you all for your advice. Sounds like I should do some monitoring and figure it out after it's up and running.
\

Originally Posted by Craig 930 RS

The inlet/outlet Andial gauge is very useful in making these conclusions - highly recommended.

Craig, would you mind posting a picture of your Andial air temp gauge?

[NathanUK]

Great thread, just wanted to say that the stock 3.2 elbow on the TB is rubber.

[polizei]

I ordered the Andial dual-read air temp gauge so I could start logging some data. At what temperature should I start to be scared? Is it best to just shut the car off or cruise around at a slow speed?

[hobieboy]

My data point... I tuned my (EFI) car around 90F intake temp. If I disable "air-temp-enrichment" my AFR could go from ~12:1 to 13.1:1 when intake air temp rises to 105degF.

Of course, if you are not pushing hard then I don't think it matters... I cruise around at 14.9:1

[spence88mph]

Didn't know that that was plastic Would you mind posting a picture of how you're connecting to the intake to the throttle body? I just presumed that it would take 3-4 vertical inches to connect to the throttle body regardless of how you were doing it.

Quote:
Originally Posted by spence88mph View Post
you don't think it would be enough? You're crushing my next project plans! You don't think the above posted intercooler would be sufficient?
What are your intercooler plans currently? It seems like you already have most of it figured out and that it's not as much of an issue as I thought. I guess an additional 3" of cooling fins/tubes could make a notable difference in some cases, now that I think about it. On a front to back IC the longest cooling tubes/fins I could use is 5", so 3" would be a 60% increase. Not shabby!

I just replaced that plastic elbow thing with a silicon 90 degree bend, it grabs much better, it hasn't popped off once. I'll take a pic this week.

I have no intercooler, just running .5bar as per the protomotive 'stage 1' kit, have been planning a MAP conversion and as large an intercooler as possible in there, just don't have the time to drive the car let alone work on it lately but fingers crossed soon. I should order an andial intake temp gauge too, how much was it?

[polizei]

Originally Posted by spence88mph

I just replaced that plastic elbow thing with a silicon 90 degree bend, it grabs much better, it hasn't popped off once. I'll take a pic this week.

I have no intercooler, just running .5bar as per the protomotive 'stage 1' kit, have been planning a MAP conversion and as large an intercooler as possible in there, just don't have the time to drive the car let alone work on it lately but fingers crossed soon. I should order an andial intake temp gauge too, how much was it?

$260ish. I think you can get the Davtron one for closer to $200. That MAP conversion would be UBER sweet, but I can't justify over $2k. I think before that I'll do headers, water injection, and brakes... It's only money, right?

[spence88mph]

Noooooo..... mapecu.com take a look, great stuff for as little as $425, I should work for them!

[polizei]

Really?? I was thinking about the Protomotive MAP conversion that Merv did. I believe that costs closer to the $2k range. We're getting off topic quickly, but I'd love to hear more about this. I wonder how involved the install is.