911 Cooling Shrouds - Improving Internal Air Distribution

[Wally]

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

[Sandeep]

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

[Massive Type IV]

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!

[Wally]

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

[Wally]

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

[Bad bug]

Thank's alot wally that's the 911 fan that i have but one of my deflectors is missing.

[Sandeep]

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