ToreB

The rear fan has two purposes: Pushing heating air to the cabin when needed, and to cool the engine. Removing it will impact both functions.
Cheers,
Tore

KNS

If the heater blower fan is used to help cool the engine (which of course it does), why eliminate it in the RS, a high performance/motorsport version of that engine? I can only guess that Porsche wanted to add it to street cars that sit in heavy traffic on hot days when the car is moving very slowly or not at all. In these situations the car has very little aerodynamic air flow around and under the car and the engine driven fan is spinning at low RPMs and doing an inadequate job of cooling. When the engine is shut down after such driving the fan may also switch on to help cool the engine.

I think a lot depends on how the car is driven (and ambient temperature) to get that fan to turn on - during or after engine shutdown. As I mentioned earlier I spent a lot of time checking out my heater blower operation and CCU to ensure correct operation. I'm in Arizona and my fan never comes on (only on one occasion when I was stuck in traffic with no where to go).

I agree with Tore, Porsche added it for a reason. I think Porsche is covering their bases and trying to think of every eventuality that the car may encounter. Since my driving and driving style has seen so little of its use, I may eliminate it (but reinstall for resale when the time comes).

JasonAndreas

*Three -- To prevent exhaust gas from entering the passenger cabin while driving in reverse.

shadow993

I used a little wd-40 to help this process. You have work it in at an angle. It will fight you all day long if you try to go straight in.

Carbon fiber option...for a few buck more.

http://www.rennline.com/Rennline-RS-...oductinfo/M09/

http://www.automotion.com/carbon-fib...Y8QaAnDE8P8HAQ

Sutton

Out of interest, did the very early 993, 964 or earlier models have the engine cooling function (after switching off the engine)?

I've seen that very early 993s (UK) had the 964 type blower unit which doesn't have the small vent at the top of the tubing so wonder whether the cooling function was available on these cars.

Apologies for the thread hijack.

EMBPilot

i dont think so, that is the job of the flappers on the bottom. the fan is upstream of that.

in addition to shadows link, here is another. i have not seen this product but it beats all the other prices in carbon, even less than the plastic one.
http://www.design911.com/Heating-Pip...More/prod4873/

Ive tested my fan various times, and only heard it come on once while the car was off. im willing to try this out for a season. The stock fan assembly comes off and goes on so easily it might be even faster than trying to work the RS duct on and off the fan duct.

i tried to work it around gradually, always got stuck at the bottom, towards the back. needed a lot of force to lock the collar into the rubber the duct. maybe its an issue on the 95s...

yes they do have that feature (at least early 95s), but dont have the fresh air snorkel thing found on later models, nor a vacuum attachment on the back.

KNS

True, but they are two separate systems. The earlier 911s (not sure about the 964) have levers that are manually pulled open and closed. The 993 "flappers" work passively.

The 2.7, 911SC, 3.2 Carrera and 964 all have heater blower motors in the engine compartment. All of them are capable of sucking in exhaust fumes into the heater duct and into the cabin. The early 993 as well. It is such a minor issue and was never a complaint in any of those cars. The legal department most likely saw it as an issue and decided it was a hazard (in 1995) and insisted that the reverse mechanism be added to the 993.

Ivan J

That is a great price. I can't help but wonder how they came up with the claim that this duct adds 6 to 8 hp...

ToreB

I can't comment on the missing fan on the RS other than agreeing with KNS notes above. The RS was meant for track use and I expect that they would try to get out as much weight as possible.

The rear fan can run in cooling mode both when the engine is running and when it is shut off. It is free to run in cooling mode when no heated air is needed to the cabin, depending on CCU temp **** setting
and the ambient temperature.

Both the 964 and 993 CCU's try to avoid exhaust fumes being drawn into the cabin when reversing. First of all, this happens only when heated air is needed to the cabin, and also depends on CCU temp **** setting and the ambient temperature.
The 964 CCU close both mixer flaps when reversing, (effectively no heated air) and the 993 switch to the upper air nozzle inlet by the means of a vacuum operated flap actuator. This actuator and air duct is mounted on the rear fan assembly, and a rear fan delete normally means removing the rear air selector as well.
Cheers,
Tore

ToSi

Minor clarification, the regular RS has the rear blower fan. The RS Clubsport version used the bypass tube.

JasonAndreas

The solenoid for the (rear) fresh air valve is energized when you put the transmission into reverse. With the front mixing chambers closed you can still get a little residual air coming through the recirculating flaps that are hidden below/behind the front seatbelt retractors (especially when they've torn slightly) depending on the air pressure in the cabin.


I don't think this functionality wasn't added until the end of ~MY95(?) (CCU version 12) along with the engine mounted fresh air flap. The 964 just sucks in exhaust fumes, just not even remotely as bad as a 964/993 cab with a cat bypass sitting in traffic...

gt3rs.

I just try to install the heather bypass tube on my 993 1996 varioram but i am stuck with all the tubes that connect to the number 2 part on your pics . Can somebody can help me with this . Where do i disconnect them and what i am doing with them ???

EMBPilot

Gt3, while my 95 didnt have any of that stuff, my understanding from researching this prior to doing it myself, was you simply cap the vacuum line that controls that flap. Should be able to obtain locally.

gt3rs.

I just found this !
https://plus.google.com/photos/11229...PaQlvO9pse7jgE

KNS

^^ Excellent!