Reverse engine cooling fan

[jwrag2000]

Have a idea to improve cooling in the Porsche 911, however it is at the expense of loosing the conventional interior heating system (doesn't really work anyway, stinks the car out with burning oil fumes). Reroute heater ducting to forward of front wheels or below front bumper, reverse cooling fan so that air is sucked back through ducting and over engine, provide some additional low weight ducting to allow the heated air to be pushed out the back of the car (maybe direct air under rear valance). Install domestic 110 volt heater with fan using power inverter to convert to 12v (seen this done on Pimp my Ride), use flapper box to direct heat as before. I believe this solution could improve cooling (air is coming from outside the engine compartment), simplify heater ducting (no need to run pipes throught cabin), reduce weight and make interior heating actually usable. Discuss.

[the]

911 heater doesn't work very well?!?

The air cooled 911 heating system is capable of turning the cabin into an oven.

It only stinks out the car with burning oil fumes if your car is a grease monkey. Fix the oil leaks!

It sucks not having any sort of heating or defrosting system in a street 911.

Finally, why do you assume the cooling fan isn't capable of providing the engine with enough cooling?

[ZOA NOM]

Hmm... not bad for post #2. Welcome aboard.

I think there might be problems with volume. The factory setup moves quite a bit of air over the cylinders. It also relies on the engine tin surrounding the motor to provide a vacuum that helps move the air. Seems like it would be difficult to move enough air through the heat ducts to keep the motor cool. It is an interesting idea, tho.

[1972_911T]

Wouldnt it just be easier to run the ductin from the front of the car into the engine compartment in to the front of the fan and save the massive hassel of trying to reverse tha fan, dont see any benefit of feeding the engine with air the opasite way infact it would probably be worse, the hotest point is the h/e's and cylinders so if you cool these first the very hot air will then be going into the cooling shroud and out into the engine bay.

Steve

[Porsche-O-Phile]

I'm toying with the idea of adding an electric fan under the engine deck lid screen to pull more air in. I imagine that alone will help tremendously and be less of a hassle.

[pmajka]

also reversing the fan will suck ground level dirt kicked up by tires into engine and engine compartment....

good thinking though

[john walker's workshop]

when the squirrels, birds and bugs start building up on the cooling fins, it will cause overheating. probably stink worse than oil too.

[1972_911T]

Originally Posted by Porsche-O-Phile

I'm toying with the idea of adding an electric fan under the engine deck lid screen to pull more air in. I imagine that alone will help tremendously and be less of a hassle.

I dont think this would help much you would need some big fan to suck in enough air to make a diff, iirc the porsche fan sucks about 800 - 1000l of air/min at 3k enough to turn the volume of the engine compartment over a couple of times a min.

Steve

[john walker's workshop]

Originally Posted by Porsche-O-Phile

I'm toying with the idea of adding an electric fan under the engine deck lid screen to pull more air in. I imagine that alone will help tremendously and be less of a hassle.

just spin the fan faster with a SC 130mm lower pulley and small hub fan.

[cgarr]

Delete sunroof, add roof scoop ducted into the engine compartment

[Jim Sims]

Given a cylinder will overheat if installed upside down (cooling fins are not symmetrical) and that minor adjustments to the baffling between and around the cylinders supposedly can make a 9 degree F improvement in oil temperatures reversing the air flow is probably a very bad idea. Maybe with a high fidelity CFD model followed by a instrumented prototype one could tell for sure; I sure wouldn't reverse the air flow on any 911 that I wanted to keep.

[dtw]

The idea of pulling the hottest air down at the exhaust side of the engine, up over the coolest side of the engine, seems contrary.

[RWebb]

the main problem here is that air just does not coll very well

may I suggest.... water?

[Christien]

Do any of you guys actually having problems with keeping the engine cool enough? Even on the track at 30+ degree C weather (high 80s/low 90s F) and my temps rarely if ever peak above 120. I've never once had to pit to let the engine cool down because I was worried about it.

[Porsche-O-Phile]

Originally Posted by john walker's workshop

just spin the fan faster with a SC 130mm lower pulley and small hub fan.

Excellent suggestion. I'll look into this also. Anything that will help with cooler temps on a magnesium-case 2.7 has to be a good thing.

[rusnak]

In the summer I go all out to keep my engine oil from getting too hot. I run 3 fans, including the heater fan and an oil cooling fan. And I degrease the engine, cylinder cooling fins, and oil cooler in an effort to make the most of my air "cooled" car.

I agree that the engine fan moves a LOT of air, especially when turning at 3K rpm. Way more than a pair of small electric fans can.

[Zeke]

Originally Posted by dtw

The idea of pulling the hottest air down at the exhaust side of the engine, up over the coolest side of the engine, seems contrary.

I was waiting for someone to realize the obvious. Good comment.

Some modified 914s have fresh air ducted to the fan. Using the existing heater ducts is one way.

[Quicksilver]

Originally Posted by milt

I was waiting for someone to realize the obvious. Good comment.

Some modified 914s have fresh air ducted to the fan. Using the existing heater ducts is one way.

Actually if it was blown from exhaust side to intake side it might help equalize temperatures from one side to another...
If a lot of other things were ignored.
The exhaust is obviously on the bottom because we want to get such a large source of heat outside of the car. That overrides any other concern so the compensation to this is to put larger fins on that side of the cylinder.

------------------
I have thought about this with the 'pie in the sky' idea of "Gee, if I could hook up a big enough fan I could make a sucker car and bend a few rules". (see the 78 Brabham "vacuum cleaner" car at Anderstorp) There is no series where it would make enough difference to try it and there are a few other reasons besides just money, why it isn't worth trying.

- Start with John Walker's bit: The first trash bag or piece of paper sucked up under the car would destroy a cylinder in less then a minute with zero warning.
- Sucking enough air mass is a lot harder then blowing a mass of air. The basic bit is sucking creates low pressure so between the cylinders and the fan you will have a low pressure area (less mass per volume) instead of the higher pressure area between the fan and cylinders that you have now.
- In truth you don't really have a fan on the 911 engine. Think of it as an axial compressor. (Yes, an axial compressor is in the fan category but...) It is an axial compressor that is carefully engineered to move a huge volume of air at maximum efficiency.
- Any reasonably sized electric fan can't come close to doing the job. Even if you engineered an extremely efficient electrical compressor the alternator required to drive it would be so large that it would require another fan just to cool it. It would need to massively change the cooling airflow to match the cooling needs of different RPMs and power outputs.

The 911 fan pushes between of 1000 and 1500 liters of cooling air through the engine each second at 6000 RPM. (depends on the engine and the fan) At the low end (1000 liter/sec) you are talking about 35 cubic feet per second or 2100CFM. A 3.2 liter uses more and would require over 3000CFM! Now where are you going to find a fan that will push that much air at pressure!!! It isn't going to happen.

BTW - Adding an electric fan to the grill won't do anything to cool the engine. A large electric fan can increase airflow to the air conditioning condenser when you are idling but probably isn't worth the trouble unless you spend way way too much time idling.

[Jeff Alton]

I would not worry too much about where the air is comming from with standard cooling system. My car has Intake airtemp sensors, they read within about 2-3C of ambient outside airtemp, in the intake.... This is the same air the fan is pushing over the cooling fins....


Cheers

[Mysterytrain]

I wouldn't use 'pimp my ride' as the benchmark for Porsche modifications. Put down the tool and step away from the car.