935 Users, Flat Fan
10-21-2003, 01:19 PM
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935 Users, Flat Fan
I am in the process of developing a "flat fan" conversion kit for the 930 type engine and would greatly appreciate input from ex/current 935 users regarding the flat fan advantages and disadvantages, IE problems with the drive mechanism, fan issues, weight of the assembly, durability and advantages realized by the extra cooling capacity.
Nearly all the Turbo engines Porsche built for racing had a flat fan and it appears that Porsche considered them essential. My understanding is that when new, the flat fan assembly cost around $5 or 6K.
The thing I find interesting is that there are so many club racers with hopped up 930's making 500 to 700 HP with a vertical (stock) fan and they seem to run fine, so why did the factory consider them necessary ?. Would the 935's have been able to survive races like Le Mans/Dayton/Sebring with a stock 930 fan ?.
Andial has loaned me a 930 case (964 will be later) to use for mock-up and my plan is to create a version of the flat fan assembly that externally appears very similar to the original. Admittedly for me, I am doing this for the "cool factor" And because I have the skill set required to do this. Oh!also I dont have the $12 g's for an old 935 set up.
The response I get from this post will indicate to me wither I am building a "one off" for my own car or if should I tool up and make patterns, create CAD files, make the fiberglass molds, etc...
Cheers to all, Paul phone 949.930.3462
Nearly all the Turbo engines Porsche built for racing had a flat fan and it appears that Porsche considered them essential. My understanding is that when new, the flat fan assembly cost around $5 or 6K.
The thing I find interesting is that there are so many club racers with hopped up 930's making 500 to 700 HP with a vertical (stock) fan and they seem to run fine, so why did the factory consider them necessary ?. Would the 935's have been able to survive races like Le Mans/Dayton/Sebring with a stock 930 fan ?.
Andial has loaned me a 930 case (964 will be later) to use for mock-up and my plan is to create a version of the flat fan assembly that externally appears very similar to the original. Admittedly for me, I am doing this for the "cool factor" And because I have the skill set required to do this. Oh!also I dont have the $12 g's for an old 935 set up.
The response I get from this post will indicate to me wither I am building a "one off" for my own car or if should I tool up and make patterns, create CAD files, make the fiberglass molds, etc...
Cheers to all, Paul phone 949.930.3462
10-21-2003, 02:16 PM
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My mechanic is an old 935 race mechanic. We talked at length about flat fans once. He noted that, among other things, they were much louder then the vertical setup. Something to consider if you use the car as a daily driver.
John
John
10-21-2003, 03:49 PM
#3
RL Technical Advisor
Hi Paul:
I used to race those for several years so I'll offer an opinion.
Indeed, they are louder but you really can't hear it over the exhaust on the 934/935.
The flat fan requires more HP to drive over the vertical fan, but the cylinder head and barrel temperatures (the Achille's Heel of these engines) are MUCH lower and the power loss was always well worthwhile in the interests of reliability of a 3.0-to 3.2 litre engine making 600-800 HP.
Alternator belts and fan drive belts were always short lived and today, I'd use a serpentine setup. Thank God for modern technology.,...
The rubber coupler (vibration damper) and bevel gears were pretty durable, overall. Due to issues with German rubber, I think a domestically made rubber coupler would be pretty bulletproof.
The root issue to bear in mind is that these are air-cooled engines and anything one does to increase airflow and cool ALL of the heads and cylinders pays great dividends in maintaining HP as the engine get hot. When the oil temps reach 210, your power is now falling off and the engine is no longer very efficent.
We even used the 935 flat fan on a 3.5 litre slide valve RSR motor that made 405 HP. It did wonders to keep good power under racing conditions.
I hope you do it!!
I used to race those for several years so I'll offer an opinion.
Indeed, they are louder but you really can't hear it over the exhaust on the 934/935.
The flat fan requires more HP to drive over the vertical fan, but the cylinder head and barrel temperatures (the Achille's Heel of these engines) are MUCH lower and the power loss was always well worthwhile in the interests of reliability of a 3.0-to 3.2 litre engine making 600-800 HP.
Alternator belts and fan drive belts were always short lived and today, I'd use a serpentine setup. Thank God for modern technology.,...
The rubber coupler (vibration damper) and bevel gears were pretty durable, overall. Due to issues with German rubber, I think a domestically made rubber coupler would be pretty bulletproof.
The root issue to bear in mind is that these are air-cooled engines and anything one does to increase airflow and cool ALL of the heads and cylinders pays great dividends in maintaining HP as the engine get hot. When the oil temps reach 210, your power is now falling off and the engine is no longer very efficent.
We even used the 935 flat fan on a 3.5 litre slide valve RSR motor that made 405 HP. It did wonders to keep good power under racing conditions.
I hope you do it!!
10-22-2003, 01:11 AM
#4
I know for a fact that the easy part is the Housing and drive mechanism. When you get around to the Fan, be prepared to sink Huge $ into this. Some time ago Porsche had some made here but they never released any for sale. Good luck! And added note here, the Fan set up is no good unless you have the Intake to go with it. I do admire you effort. I think the very thing Porsche never count on is American Ingenuity.
10-22-2003, 01:08 PM
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I posted this earlier on the Pelican site a few days ago:
Believe it or not, the most difficult part of this project is the 90 degree gear box and it's mounting system. The bevel Hypoid gears 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.
Now for an update>
Today (wed) the German gear manufacturer has refused to sell me the gears for this application. Even though they are rated at 25,000 hours @ 7500 rpm with grease lube, they will not guarantee even 500 hours @ 11,000 rpm with pressurized oil jet lubrication.
This gives you an idea of the stress the gears are under. Back to the drawing board... I have a plan.
The fan and stator mounted below the fan are completed and have been tested to 12,000 rpm. That was the easy part.
The problem is the gear box.
Cheers, Paul
Believe it or not, the most difficult part of this project is the 90 degree gear box and it's mounting system. The bevel Hypoid gears 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.
Now for an update>
Today (wed) the German gear manufacturer has refused to sell me the gears for this application. Even though they are rated at 25,000 hours @ 7500 rpm with grease lube, they will not guarantee even 500 hours @ 11,000 rpm with pressurized oil jet lubrication.
This gives you an idea of the stress the gears are under. Back to the drawing board... I have a plan.
The fan and stator mounted below the fan are completed and have been tested to 12,000 rpm. That was the easy part.
The problem is the gear box.
Cheers, Paul
10-22-2003, 03:46 PM
#6
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Paul, not sure if it helps, but I recall reading an article in Excellence (not sure how old) about this. Martin Schneider of MSDS converted a 914-6 to run a flat fan setup (it's also a 3,2 litre twin turbo!). You may already be familiar with it, but if not give Martin a call, he might be able to provide some assistance.
