Where to find the type 935 flat fan?

[82SC]

i wonder if there was any oil for the gears in that unit...to cool it...well I hope someone who is smater and more creative then I comes up with a solution...

MJ

[HawgRyder]

After seeing the real setup....all it would take is a support housing for the 90 deg gearbox.....and an extension to allow an extra bearing out by the pulley.
Not hard at all.
The big problem would be the fan and housing.
I would think that mounting the altenator out by the pulley would work better....perhaps in a serpentine style belt arrangement.
Hmmm...back to the drawing board....LOL
Bob

[alfa11]

I recently ran across this thread while doing research for my latest project, building a replica 935 flat fan. Porsche recognized the necessity for improved cooling on the turbo engine when exceeding 450 HP. Virtually all the air cooled turbo race engines built by the factory were the flat fan type. The fact that so many make due with the stock fan while exceeding 450 horse power (by huge amounts) is testament to the quality of engineering in the 930. The flat fan provides much more cooling air (up to 1600 liters per second) and more important, even air distribution to all cylinders. With this set-up you can bump the boost an extra .05 Bar (18-20 HP) and have a much greater safety margin regarding detonation.

I am told that others have tried to reproduce the flat fan and that they have exploded. Let me qualify myself here, I am an ex F1, Indy, IMSA fabricator and have skills in machining, composites, metal fabrication and "rapid prototype" technologies. This particular project requires all those capabilities. I currently manufacture the replica Bosche twin plug rotor exclusively for Andial and will be doing the twin plug cap later this year. My normal 8 to 5 job is fuel cell integration for the major auto manufacturers.

Believe it or not, the most difficult part of this project is the 90 degree gear box and it's mounting system. This will be the most tortured mechanical part on the whole car. The fan will be rotating up to 11,000 RPM and pulling 3500 cubic feet per minute at 7500 RPM engine speed. Consider the engine running at 7500 RPM, the driver has one of those "Oh ****" moments and slams on the brakes, the fan has to decelerate from 11,000 to 0 in a tenth of a second. Also the gear box must transfer up to 15 HP at a 90 degree angle to turn the fan at that speed and is constantly changing RPM. On top of that there is also heat, vibration, etc.. transmitted through a gear set that is less than 2" in diameter. Unfortunately near aerospace gear quality is required here. The new 935 fan will have a gearbox made in Germany that has pressure lubrication and "lapped" spiral bevel hypoid gears made of a special type heat treated steel. I tried finding these in America, but could only find gears (without the box) in matched sets for $1800. The German product cost more, but at least it is a complete gearbox.

Andial has provided me with a 930 case to use for mock up of the flat fan. The fan and the stator that is mounted below the fan are nearly completed. The 90 degree gearbox should be on order this week. Mounting system for the gearbox will be similar to the original 935 as will the fiberglass shrouds. Alternator mount will be in the same place but tidied up and simplified. At this point I plan on using one of the small Japanese 60 amp alternators. They are lighter, have better cooling, cheaper and have reasonable durability at the required speed. My goal is make a flat fan system that externally will appear to be original to all but those who have actual work experience with the original 935. The "first articles" should be complete this Jan/Feb and will be engine dyno'd at Andial. Hopefully we will be able to do back to back testing of vertical VS horizontal fan with temp mapping of all six cylinders on the same engine. Pricing is a guess at this point, probably about what Porsche wanted for the flat fan set up when new, around $5500.

Any input from 935 users past or present, future customers and knowledgeable experts in the various fields involved here would be greatly appreciated !!

Cheers to all, Paul

[Matt Holcomb]

George,

Why not just buy a complete 935 engine.

http://www.holscope.com/935_engine/


Matt Holcomb
MFIWDP
1974 911 Carrera 2.7 (RoW)
Dedicated Homepage
Engine Rebuild Homepage
Pelican Gallery Profile

[campbellcj]

I saw one at Ottos (Venice, Calif) not too long ago and believe it was for sale. Not sure about the completeness or condition.

[nick-moss]

Here is THAT SOUND

[Shuie]

John Starkey had one a while back.

http://www.johnstarkeycars.com/

I saw it in an ad shortly after seeing the the black 914 in Excellence. I thought it would be cool until I realized how rare and expensive any parts for these cars are. John had already shipped the fan assembly he had to a guy in the Netherlands for 2x the money I currently have in my '73.

If you really want one, give him a call. He knows a lot about these cars and will know if/where an assembly is for sale.

[SteveStromberg]

If you really want one We can supply one for you. Steve


www.ottosvenice.com

[cegerer]

Not exactly your standard 911 ......

[jyl]

Reviving this old thread - any more news about an after-market fan flat kit?

[alfa11]

To All,

I have given up my quest to recreat the "flat fan". Lack of general interest and cost being the major reasons. Several 930 racers I contacted felt they were happy with engine temps and the life span of there engines and could not justify the added cost ($3500) for the flat fan set up.

Cheers, Paul

[jyl]

I was thinking that a clutch or viscous coupling could be used. This would relieve the fan and gearset revs from having to instantaneously match engine revs, and perhaps then lower the cost and bulk a bit.

[82SC]

i hear you can find a aerospace quality 90 degree gear set from salvage helicopters...yes helicopters....

hmmm...too bad you gave up on this project...
but wait you are making 12 plug caps too...hmmm...wonder how it will compare to burn-bros...

[alfa11]

Ive seen the helicopter stuff and its all too big. The only suitable drive system I found for less than $1500 came from Germany (naturally) and is used for high speed machine drives.

I was initially attracted to the viscous drive system until I got into the pump, cooler and regulator that go with them, it all ends up a plumbing nightmare in an already cramped space. Lot of added weight too.

Really it came down to a lack of interest with prospective customers. What is Burn-Bros?

Cheers, Paul Oh heres a pic of my former glory......

[82SC]

search on the board, he is on the brink of adapting the 12 lead jag cap to SC dizzies

[jyl]

Someone makes, or once made, a flat fan conversion for VWs. Go to the bottom of this page.

http://www.ismi.net/riecherttuning/coolingt4.htm



Kind of weird looking but certainly cheaper than $3500.

According to the following page, the above design is prone to throw belts but that can be resolved with an idler pulley.

http://www.tunacan.net/t4/tech/upright.htm

[Jared at Pelican Parts]

Originally posted by BlueSkyJaunte
A recent issue of Excellence had one slapped on a crazy-ass 914 with a turboed 6. The guy paid $8k for it in really bad condition, IIRC.

THats Marty Schnieder's car. It''s a work of art. Something close to 500HP out of that thing.

[Shuie]

When I called John Starkey about the one he had for sale, I had no idea who he was or how rare a real 935 was. When I asked him how much he sold it for, he told me $18k

There are some really resourceful people hanging out on this board. Between beepbeep, BURN-BROS, A Quiet Boom, souk, and jpnovak, I have no doubt that someone here could design, source the parts, and build one of these within a few months.

[MACHINEMON]

Does anyone have a print of this part or have a scrap piece that could be used to reverse engineer this thing? It could be done. I have a friend who has a CNC machine shop and casting experience. If it just had to be functional, a CNC/welded assy would not be too hard....If anyone wants to give it a try I will pull my weight with ACAD models and machine shop coordination. The VW guys have a 911 style fan for about a $1000.00. We should have a 935 style if we wanted...

[MACHINEMON]

Ooops, just read Alpha11's post. I did not realize that it was so highly stressed. Could it be made with a one way clutch so the fan did not have to de accelerate with the engine? Anyway, if i can help let me know....