Clutch-Type Engine Fan

[JBSC]

Sleepers Speed Shop (Costa Mesa, CA) and Gary Castillo are in the process of developing a clutch-type engine fan for SC/964/993 engines. The fan will engage on throttle, at idle, or when the fan rpm otherwise drops below a certain threshold. The fan would effectively be decoupled when off throttle, and engage with throttle input, running off of the engine rpm. Theoretical gains include more efficient engine cooling and better engine response.

Opening this thread up for discussion, and also curious to hear from anyone who has seen analogous designs elsewhere (automotive or otherwise).

[Uwon]

Confusing to my hard head. From your description, the fan would only be off on desceleration, am I correct? Or, when holding steady at say 2,500 rpm as well?
Johan

[Driven97]

Per the way your description is worded, they're installing a one-way bearing between the pulley and fan? I don't see any worthwhile benefit, unless I'm missing something.

[GH85Carrera]

I am pretty sure I want my cooling fan running ALL the time. Especially in hot weather. When oil temps hit 210 I turn on my oil cooler fan. I would never accept a fan that does not run all the time. The engine get HOT really fast when the fan stops.

It ill take some magical numbers to convince me otherwise. But if is ain't my car, I don't care. Good luck.

[stownsen914]

If the clutch disengages the fan when the engine is at low or no load, then the drop in parasitic loss from the fan (net power gain) isn’t when you’re on the throttle ... which is when you’d want extra power.

[JBSC]

Of course, a video would have helped.

See below:

https://www.instagram.com/p/B2pcCP-l785/?igshid=1w5irtqjx1rxo

[porsche930dude]

Agree i dont see much benefit from that. A thermo fan clutch like in a normal car would be great but theres no way to heat it without a radiator

[porschyard]

Far from an expert here in matters like this but i would never want my cooling fan disengaged on my air cooled motor for any reason.

[techman1]

Hmmm.
In looking at the video, and thinking thru the description, and the video:

This appears to allow the inertia the fan develops, like at 5000 motor rpm, to not be lost when you come to a stop, or take your foot off the gas. The fan would keep "coasting and cooling", even though the engine was at 800 rpm. When fan speed dropped to engine speed, it would then be driven by the engine at that speed. Or am I wrong? sounds like a neat way to allow more air to circulate!

[David Inc.]

Edit: ^^ ahhh that makes a little more sense. Thinking of a fast up-shift you'll be dropping two thousand rpm but the fan will be coasting in the mean-time. You won't have to bring it down 2000rpm and you might have a few hundred rpm to accelerate through before the fan comes back down to the matching speed. Interesting--curious to see how much impact it has.

Only time I can think that this would be a help would be during cold start warm up. Limiting airflow over the engine to only that needed to prevent hot-spots, but not really providing too much cooling.

Track days in cool weather are always a pain because of how long it takes to get the engine warm.

So in that case maybe...is this what they're going for?

[Marc Bixen]

Porsche started installing an alternator clutch bearing on all manual trans cars starting with 996's. Tiptronic and PDK don't use it. The actual reason for the clutch release, and remember on air cooled cars, the alternator is behind the fan, is to prevent over-rev on high rpm shifts. Track guys will get this. What happens is that at high rpm when you depress the clutch the centrifugal spinning force of the alternator will actually cause the rpm to go up another 200-300 rpm after you push the clutch pedal and lift off the gas, thus creating an over-rev. Very common on 964/993 track cars. I've never heard of this causing over-rev type damage, but it is a little disconcerting, and does slightly slow down your shift, which equals increased lap times. Not what you're looking for. Cool innovation guys, thinking outside the box. I'm sure there are other bonuses from this also, maybe increased cooling, as the fan continues to spin at higher rpm than the engine on decel, as well as possibly slightly better fuel economy. I've thought about something like this ever since learning about the system on 996's. Thumbs up. Hope you can market it well.

[Driven97]

Originally Posted by Marc Bixen

What happens is that at high rpm when you depress the clutch the centrifugal spinning force of the alternator will actually cause the rpm to go up another 200-300 rpm after you push the clutch pedal and lift off the gas,

Can you explain this? For the motor to speed up, additional energy needs to be added. The fan/alternator only ever takes kinetic energy away from the system.

[Marc Bixen]

Drive one and try it! It behaves like the car has a secondary flywheel. The spinning mass of the alternator while accelerating, wants to continue accelerating momentarily when the clutch disengages.

[Dr J]

I like the idea. Will definitely result in extra cooling.

[Driven97]

Originally Posted by Marc Bixen

Drive one and try it! It behaves like the car has a secondary flywheel. The spinning mass of the alternator while accelerating, wants to continue accelerating momentarily when the clutch disengages.

That's not how physics works.

[techman1]

Yep. recall old physics class.
Something about objects in motion, force to move, remove that force, start slowing down due to forces already applied, friction etc.

[pampadori]

so is the alternator also spinning? I'd like to see how this functions when there is an electrical draw like you'd see with a stereo and fans and headlights on.
I think the motor in the video might be lacking a functioning alternator.

[chrisbalich]

This is super cool.
I'd like to see the packaging. It seems like it pushes the pulleys away from the engine. Seems like there'd be no way to run AC and this....but no one interested in this is running AC anyway.

I'd run one in my car for sure.

[JBSC]

Originally Posted by Marc Bixen

Porsche started installing an alternator clutch bearing on all manual trans cars starting with 996's. Tiptronic and PDK don't use it. The actual reason for the clutch release, and remember on air cooled cars, the alternator is behind the fan, is to prevent over-rev on high rpm shifts. Track guys will get this. What happens is that at high rpm when you depress the clutch the centrifugal spinning force of the alternator will actually cause the rpm to go up another 200-300 rpm after you push the clutch pedal and lift off the gas, thus creating an over-rev. Very common on 964/993 track cars. I've never heard of this causing over-rev type damage, but it is a little disconcerting, and does slightly slow down your shift, which equals increased lap times. Not what you're looking for. Cool innovation guys, thinking outside the box. I'm sure there are other bonuses from this also, maybe increased cooling, as the fan continues to spin at higher rpm than the engine on decel, as well as possibly slightly better fuel economy. I've thought about something like this ever since learning about the system on 996's. Thumbs up. Hope you can market it well.

Thanks, Marc. Exactly how I thought of it. Didn't know about the 996/997/991 analogy. Looking forward to seeing how their R&D progresses.

[76FJ55]

Originally Posted by Marc Bixen

Porsche started installing an alternator clutch bearing on all manual trans cars starting with 996's. Tiptronic and PDK don't use it. The actual reason for the clutch release, and remember on air cooled cars, the alternator is behind the fan, is to prevent over-rev on high rpm shifts. Track guys will get this. What happens is that at high rpm when you depress the clutch the centrifugal spinning force of the alternator will actually cause the rpm to go up another 200-300 rpm after you push the clutch pedal and lift off the gas, thus creating an over-rev. Very common on 964/993 track cars. I've never heard of this causing over-rev type damage, but it is a little disconcerting, and does slightly slow down your shift, which equals increased lap times. Not what you're looking for. Cool innovation guys, thinking outside the box. I'm sure there are other bonuses from this also, maybe increased cooling, as the fan continues to spin at higher rpm than the engine on decel, as well as possibly slightly better fuel economy. I've thought about something like this ever since learning about the system on 996's. Thumbs up. Hope you can market it well.

Just my rambling thoughts:

The inertia of the alternator will not cause an over rev. It will only slow the RPM decrease on deccel. The clutch is engaged on acceleration , so performs just like a standard pulley.

The clutch is there to preserve belt life and to keep the inertia of the alternator from causing the belt to go slack on the non-tensioned side of the belt run and jump off.

https://www.ntnglobal.com/en/products/review/pdf/NTN_TR75_en_P124.pdf

From looking at the video it appears that the alternator is still directly connected to the belt via the fixed pulley as the pulley nut is stationary when the fan is freewheeling with the engine stopped. I don't know the rotational moment of inertia of the fan vs the alternator, but I would guess the alternator is the greater of the two, steel rotor with heavy copper winding (though a smaller diameter), so I'm not sure how significantly the belt tension will be effected by the decoupled fan with the alter still connected to the pulley. There is also reduced risk of belt path run length change on an air-cooled than the 996+ due to the tensioning method. With the 996+ the tensioner is a spring-loaded unit so when the inertia of the alt is driving the system it is actually applying tension to the tensioner side and in theory could compress the tensioner and cause the belt to go slack on the normally tensioned side. On an air-cooled car the tensioning is accomplished via adjusting the diameter of the upper pulley, so regardless which it driving, the crank or the alternator the belt run is a fixed length.

There could be some slight benefit in additional cooling, but again I’m a little skeptical. I understand that the fan will continue to free wheel when the engine is shut off, but the speed the fan is freewheeling at may only see a small pressure differential across the fan. It would be more interesting to see how long it takes for the fan to drop from high RPM to idle RPM. One possible method, video using a strobe and with a make on the pulley and one on the fan, run the engine to high RPM then release the throttle and see how long it takes for the fan and pulley to start rotating at the same speed. If the fan actually has enough momentum to maintain an RPM split for a significant time, then cooling is possibly improved, but if they return to matched idle speed shortly after throttle release, then I would guess you won’t see any significant change in cooling performance.