tedesco

I did a check of the intercooler efficiency on my car. With about 1.4 bar (20PSI) boost I measured the temperature directly at the exit of the turbo and behind the intercooler just infront of the throttle butterfly. My results at 21°C ambient temperature were:

- 136-140°C at turbo exit
- 43-45°C behind the intercooler

I used an instrument that stors max and min temperatures, so I can comfortably read the number after a run. According to these measurements the intercooler efficiency would be around 80%. I was a bit surprised with those results as I did not expected to see such a compareably good number considdering the bad ducting of cooling air behind the intercooler. Certainly is it possible to improve the situation but compared to other peoples thinking I would rather start with some hood louvres or ducting like on the 968 turbo than swapping to aftermarket intercoolers. I did not measure the pressure drop through the intercooler jet but what I like about the stock intercooler is its square crosssection which I belive to be superior in terms of flow capacity compared to the often thin but heigh aftermarket intercoolers.

JustinL

Very interesting. What sort of heat soak conditions were there? Did you do the run with a dead cold intercooler or was this a track day type measurement?

streckfu's

Good post. Thanks for the numbers. They seem much better than I have been lead to believe.

Laust Pedersen

Thanks for sharing. That’s very good to know for those planning upgrades.

Could you reveal a little more about the measurement conditions?
What gear and what speed?
Were these thermally “steady state” measurements?
If not, what would you estimate the start temperature of the IC was? And how far after the 20 psi was reached were the measurement(s) taken?
The aluminum intercooler itself starts out at a certain temperature and has a certain heat capacity, so if the IC starts out cold the outlet temperature will slowly climb until steady state is reached.

For those not interested in holes in their hood (holey hood ), extra flow over the engine can be gained by removing the outer thirds of the firewall molding with cabin smell at low speeds as a side-effect if the engine is not squeaky clean. Claus Groth did the investigation some time ago.

Laust

toddk911

Well, those numbers prove why many have said "do not worry about a new IC until 400+hp"

tedesco

A few more details about how the test was done. I drove the car on normal open roads with little to no traffic at night. After the engine warmed up, the runs were done by accelerating from 2nd to third gear till rev limit. This certainly did not last long enough to assume it was a kind of steady state running but you can imagine that with 1.4 bar you never realy accelerat for a long time. After each run there was a cool down periode with normal crusing. The temp sensors I used were wire types. that means that they look like two 0.5mm electic wires which have been soldered together at the tip. The heat capacity is very little as there is basicly only a ball of metal to heat up with a diameter of about 1mm. I tested the response before and they react very fast. As metioned before, the instrument recorded the max and min temperatures during the run and I don´t have continuose readings. For the calculation I just looked at the maximum readings. The data was very repeatable. I know that this is not a scientific set up but it corrosponds to a normal street situation. I am not so shure about the intercooler itself to cool down a lot during crusing because of the heat radiation of the engine and the radiator in combinatioin with little air flow through the engine bay because of low driving speeds. Nontheless I would expect to see a small influence from the heat capacity of the intercooler material but just by guessing I would not belive that the efficiency would drop by lets say 5%.
One important thing I totaly forgot: I have got the 924 turbo style nose panel mounted which might aid cooling. Now that I remember it again it might be worth taping it to see if there is any difference.

toddk911

"One important thing I totaly forgot: I have got the 924 turbo style nose panel mounted which might aid cooling. Now that I remember it again it might be worth taping it to see if there is any difference."

One day I was out on the interstate and got a piece of cardboard that flew up and stuck to the front of the car. I can not say for sure if it was more covering the IC inlet or the radiator itself, but after several 4th gear full boost runs the engine temp went up noticably. To the point that I pulled over, noticed the cardboard and got back on the road and everything was fine.

Needless to say it proves airflow over either the IC or radiator makes a big difference.

VWaddict

Thermocouples.

Keith

Perry 951

Likely K Type Thermocouples – they react very quickly, and as long as you have a good logger, very accurate.

I am also data logging turbo out, intercooler out, and combined exhaust. I'm at about 65% average efficiency at peak temps of 315F at the turbo exit; 18psi on K27/8.

I made a huge mistake and removed the shroud around the intercooler, so I'm getting a lot of airflow past it. I think this will bring the efficiency up. Well, sooner or later I’ll have the data to show it.

80% is pretty good and is the most common % I hear around here.

IanS

Well, there is another potential issue besides efficiency, which is flow.

I think the rule of thumb is 2cfm of flow equals a horsepower worth of air. At one bar of boost, it should be approximately 1cfm=>1hp. Based on Lindsey's flow measurement of 205cfm for the stock intercooler, our intercoolers should be good for 205hp worth of flow. Obviously you can flow more air, but you get a larger pressure drop.

So with the stock turbo, the intercooler appears to be about the right size. If you're flowing more air, I would expect it to be a restriction.

But just like running a 2.5" exhaust instead of 3", its not going to prevent you from making more power, it just makes it a bit more difficult.

TurboCab

How about pressure drop acoss the intercooler?

RKD in OKC

Lindsey Racing has testing done with stock, stage1, and stage 2 intercoolers on their site under intercoolers. The chart has pressure drop and temp in and temp out on the intercooler. They used hard pipes with sensors in them.

tedesco

Hallo again. Here are the next numbers. As prommised, I checked the effect of the vented nose panel. My one looks exactly like the one on Perrys 951 which is shown a few posts above. The way I did the test was to do two runs with closed (taped) nose vent and than to remove the nose vent and repeat the test. Here are the numbers:

- Vent OPEN: compressor out 146°, intercooler out 51°, ambient 29° (a bit warmer than the first measurements)

- Vent COLSED (like stock): compressor out 143°, intercooler out 45°, ambient 29°

So according to the data the vent in the nosepanel IS BAD for charge cooling. I was not overly surprised to see that because the opening of the vent in the nosepanel is in an area where I would expect to see some suction. The nosepanel I have got came directly with the car and the stock panel was not available any more. In any case another item on which you can safe money.
One more note to the results: You might have noticed the 3° compressor outlet temperature difference between the two tests. This might well be the difference due to the heating up of the intercooler core material itself as somebody suggested in one of the post above. It would correlate quite well with the inlet temperature that I measured which was 27° with the engine beeing cold at start and went up to the above listed 29° with the engine at operation temperature. It is only 2° instead of 3 but I would not claim my results to be more accurate then +/-1° anyway.

What I want to state clearly is that this measurement was done with the 924 turbo style panel and not with the Lindsey racing panel. The L-racing part has go a raised lid that stands proud of the hood so the influence to cooling might be different and I did not measure it.

Next on the list (was on the list already for a long time) would be a pressure measurement. I prepared the wireing loom and the data logger since about 1/2 year but did not find the time taping all the sensors in but I keep you updated and be back with some results.

por4ever

Tedesco, thanks for the test. I was planning on the nose vents but now I will have to reconsider. I still think they look cool though.

I know a lot of people have talked (argued) about the differences of the two panels but you are the first that has actually made the measurements.

special tool

Probably a good bet to start your 951 tuning in another area (turbocharger, for instance ) since I have blown 500 plus wheel HP through a 100% stock intercooler on numerous occasions now.


I DO use a hood vent, however.......................................

I have had some success copying the updates that Porshe itself made on later models - they do know a couple of things, I guess.