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Old May 16th 2005, 10:06
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911 Cooling Shrouds - Improving Internal Air Distribution

Hi all,

I have been playing around with this shroud for a few weeks now and along with my datalogger, have what I believe to be an accurate baseline to compare any modifications to my FAT 911 cooling setup. I'm using stock T4 under cylinder tins.

I have tuned my engine the best I can and it seems to be running well. I have quite a few graphs produced by my logger and have noticed some interesting points:

1. With the unmodified shroud and stock 11 blade fan/ alternator ring, as the engine warms up, #1 and #2 warm up slower than #3 and #4. The slope of the graph for these temps over time indicate that #4 warms up twice as fast as #1. (Is #1 receiving twice as much cooling air as #4 ? :shrug: )

2. After a hard run up to 140 kph from a dead stop, and then coming to a dead stop and idling (900 rpm) for 5 minutes ... #1 cools down twice as fast as #4. The cylinders seem to cool down with #1 cooling the fastest, then #2, #3 and then #4. #1 cools at the rate of -0.35F / Sec and #4 at -0.18F / Sec.

3. By taking the fanbelt off and starting the engine and letting it idle, all 4 cylinders warm up at the relatively the same rate ... making sure its not a tuning issue causing the temp imbalance.

4. Driving the car in 5th gear at 115kph (3000 rpm) vs 4th gear at 88kph (3000 rpm) creates temps 25 degF hotter (engine load im thinking)

I'll post some pics of how the 911 alternator ring has 4 built in diverters that seem to direct airflow in this shroud. The airflow of a 911 axial fan spins clockwise and I have a cool picture of an axial fan showing the airflow pattern and air distribution in free air.

My plan of attack is to place diverters on the back of the alternator (alternator cap ) similar to a stock 911-6 setup to start, and working with the alternator ring diverters

So ... does anyone have any suggestions on how to equalize the airflow (swapping to a DTM does not count ) ? I have my own ideas but it would be great to place all of this information in one thread, where everyone could benefit from this information. I'm not looking to market this product, just love the look and sound of this setup and want it to cool more effectively.

Sandeep
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Old May 17th 2005, 06:36
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Hey Sandeep,

Cool idea, lets give Jake a head start for s/th he plans on doing in the future as well

Funny, I experienced roughly about the same findings as you did. They are also consistent with the data that Jake had on his site (and this forum) AFAIK some time ago, just after his tests.

I say roughly thesame, because my temp differences between 1 and 2 AND 3 and 4 were very close, but that may partly be due to the fact that I used (porsche 964) Nikasil cylinders.

I also installed the stock diverter (it just fits a BAS shroud with only very minor mods) and even enlarged it. Utimately, it made nr. 4 cylinder run cooler than nr. 3 : Oeps

Since my oil temperatures kept a stunning 85 degrees Celcius (185F) at all revs (!) and since I believe that the cylinders are a major factor in cooling the oil (apart from the actual oil cooler of course) and because my top cylinder fins are very small, which creates a huge barrier for air to flow over the first cylinderhead fin, I went as far as to put an almost horizontal plate over the cylinders to increase flow towards and over the heads. I will have pics in a few days I hope.
Anyway, that gave a 50F lower head temp! with the same oil temps. 1 and 2 are still lower in temp overall than 3 and 4, but that will be the goal for step 3

The difficulty is that there are a lot of factors into play here. For instance, I have used the 11-blade fan with the 245mm diameter blades and a 90mm pulley on the fan and a 140/145mm pulley on the crank.
I have also tried the 12-blade fan which has a 100mm fan-pulley and 255-ish fan diameter. The 12-blade also has a totally different housing air-outlet; more straight than the 4 curved ones you spoke of. I have a picture of the latter one if you want it posted (I have before). I have done too little runs with the same conditions to be able to say s/th conclusive about the differences on that one yet.

- end of report - (for now)

Regards,
Walter
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Last edited by Wally; May 17th 2005 at 06:42.
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Old May 17th 2005, 14:01
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Wally,

Its great to hear you are having success with your 911 setup. I too believe that the stock 911-6 diverter on the back of the alternator is key. The 964 fan diverter is indeed a work of art, perhaps an improvement over the SC 11 blade setup.

I have ordered an SC diverter, hope to have it in a few weeks. I will install it with mods if need be and see where my temps are going to end up. Up till now, my max temp difference between #1 and #4 are averaging 70 degF while 1-2 side and 3-4 side are up to 60 degF apart. 1-3 and 2-4 are 24 degF apart because 3-4 are higher than 1-2.

Please post pics of that horizontal plate you are talking about .. would be interesting to see.

Sandeep
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Old May 19th 2005, 11:16
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Sandeep, the first step you should take would be to increase the drive ratio like we spoke about when I met you. This is easily done with the later model Porsche top pulley.

The shroud you are working with has a few physical challenges that will limit your work that can be done without actually modifying the shroud's skin.

Your primary objective should be to effectively divert more air flow to the #2 and #4 cylinders as they are the hottest due to being almost directly under the fan and air generally does not like making a 90 degree bend... At least without being directed efficiently.....

I am glad to see that you are making this development- You will undoubtedly see just how difficult air can be to manipulate, I never would have dreamed that it was so difficult to work with.

The differences in temps arenot as great as I saw. This could be directly related to two things:
One is your climate, its cooler where you are on ambient temps and also that your gearing may be shorter and not placing as much load on the engine thus not showing all the data to its max extreme. In some of my tests I installed 28" tall tires on my car to effectively gear the vehicle up to place more load on the engine and create more heat with less fan speed- thats when the differences really came out in the car just like they did on the dyno, and even more in some instances. Doing this allowed me to develop the TI shroud to even a higher level than most people would ever be able to push it to..

Also the smallest engine I tested was 153 BHP-

Kep it up, you'll learn a ton!
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Old May 19th 2005, 16:21
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Sandeep,
This is the 12-blade backside:



Note that the original 964 cone is missing here (still need to get that one )

I really like the way the air is directed out in a straigth way. Also that that is done by a multitude of air diverters, which are also longer overall than the 4 on the old fan houses. Theoretically, it would make it easier to divert the air to 3 and 4, if half the work is already done inside the fan housing!

It would only be logical that porsche would upgrade its parts during the production of its aircooled boxers

Greets,
Walter
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Old May 22nd 2005, 14:02
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As promised, here's a picture of the original cone air deflector of a porsche 11-blade 245mm fan/alternator combo:



And here's a preliminary air deflector I made to direct more air to the heads and to overcome the barrier of the first cooling fin. This is because the fins on the nikasil 964 cylinders I use are very small (therefore low, so the heads fins stick out a lot). It gave a 50F lower head temp
The 964 cylinders have M6 thread on top of the cylinders, so I could mount to that. Originally on the porsche 964 those holes are for mounting the knock sensor bridge...



The original air deflector/cone did gave slightly lower head temps for 3 and 4, but not as much as I thought they would. Enlarging the area of the cone air deflector did work, but still not enough to my liking compared to the temps of 1 and 2.

Work in progress
Walter
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Old May 24th 2005, 08:45
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911 fan shroud

Thank's alot wally that's the 911 fan that i have but one of my deflectors is missing.
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Old May 24th 2005, 09:52
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Thanks for the comments Jake.

I reprogrammed my logger to flash an LED when the hottest temp from any cylinder reaches 375F. On a full acceleration run from a dead stop, gas pedal to the floor in each gear, 5500 rpm shift, #4 hits 375F at 4th gear, 3800 rpm consistently.


Thanks for the pics Wally.

In the diverter picture, it looks like you may only be getting 3/4 of the airflow from that quadrant as it looks like some air may getting past that last diverter to the left in the pic, if you compare it to the alternator guide diverter. I know you are using the 964 setup now though.

My idea is to use 3 diverters, one each directly behind the stock alternator ring diverters and one in between to make 2 channels to capture all of the airflow of that quadrant of the alternator ring. This will mean changing the positions of the factory alternator cap diverters.

The factory alternator ring diverters look to be of an airfoil design and I will try to incorporate the airfoil shape into my diverters placed on the alternator cap. I will keep placing diverters around the alternator cap, taking more air from each neighboring quadrant on the alternator ring until I can equalize the temps. That is the plan anyways ! Who knows if it will work until you try it.

Sandeep
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Old May 24th 2005, 10:15
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Quote:
Originally Posted by Sandeep
I will keep placing diverters around the alternator cap, taking more air from each neighboring quadrant on the alternator ring until I can equalize the temps.
Sandeep
Yes, that should be 'relatively' easy to do. However....it may result in that you take air away from your cooler running 1/2 side to a level where both sides run equel temps, but generally too high!
I think you need to direct the air also to flow from top to bottom over the heads. That is the direction of the fins after all!
To accomplish this, I think I also need more room in my shroud, at least more above the heads. My simple 'steel plates' over the cylinders won't cut it, but it is a start in that direction. I also think that dumping the air from above is the key succes element of the type 1 cooling way: its in the direction of the fin area (duh..!)
The more advanced shrouds (which I consider the Klaus, Remmele and RMB ones, maybe even Gerd Weiser's shroud) do seem to have more room above the heads in the shroud and even more above the 2 and 4 cylinder than over the 1 and 3 cylinder. Not by chance I think. Those shrouds are also 'flatter' right behind the fan. Probably to even out the left/right side flow better. Ever noticed that?

In the end, you very likely to end up redevelop/design your own shroud. Jake is probably right about that

Regards,
Walter
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Old May 24th 2005, 11:38
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Great points Wally. By equalizing the temps in the way I mentioned, you are right ... they won't nessesarily be cooler (hotter I would think) but they may be even

The airflow must be directed from top to bottom as you have mentioned. Check out Remmele's website under his pictures section and look at the pic of the inside of his shroud ... it is quite flat right behind the fan and it looks like this dumps the air vertically between the cylinders.

I'm sure this shroud uses the 964 setup and with the vanes you have shown on the 964 fan, you are much further ahead than I, I would think, down the road to improving cooling.

Perhaps a 964 fan setup is in my future ?

Sandeep
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Old May 24th 2005, 16:19
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Quote:
Originally Posted by Sandeep

I'm sure this shroud uses the 964 setup...

Sandeep
Thanks Sandeep
The 'new' curved fan blade houses and fans/generator combo's you can buy at bug stores 'everywhere' do NOT use the housing of the original 964!! So, AFAIK, you still get the old 4-vane style fan housing. That fan housing is a new mould, where a Valeo generator fits in nicely. Also, the original 12-blade fan is turned down to a 225 size if I am not mistaken. Anyway, a considerally amount of original fan blade is removed from the tips. I don't know how that effects cooling air.
Probably 'they' thought that the amount of air was more than enough, maybe even to much (as Jake also has said sometimes), so it would be no problem. I don't know...Most 'old-style' german tuners still prefer the old 11-blade I heard once...
So don't be put down by the 11-blade: its damn good; it just needs to learn to behave in the presence of our type 4's

Regards,
Walter
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Old May 25th 2005, 08:32
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I feel left out. I don't have any data to share but i do think if done right the 11 blade will work. Samcat had a 11 blade setup that di work well on a stock 2.0l type4.
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Old May 26th 2005, 13:45
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I have finally received my 11 blade fan factory diverter in the mail ... time to start playing and logging the data

Its a good thing the 911 fan/alternator setup can be removed from the shroud and unwired in about 3 minutes :agree:

Sandeep
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Old May 26th 2005, 14:03
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Cool!
Curieus what your accurate measuring device spits out
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Old May 26th 2005, 14:34
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That datalogger of mine is using I/C's accurate to 1.0C, converting to F, accurate to 1.8F.

My VDO oil temp gauge/sender is off by about 12F at 180F oil temp measured in the DS tank. My logger reads 180.8F, and an infrared thermometer measures in at 179.8F

Sandeep
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