Heat Consistency IDEA.

[wwest]

We don't drive the 911 ('88) very much in the wintertime but the other day, sub-freezing, we got caught in some slow moving stop and go traffic. Wife soon complained about the "too much heat" whenever the engine RPM rose with each downshift/upshift series.

So...Why not eliminate the engine cooling fan airflow for heating and just rely on the cabin heat blower for a CONSTANT level of heat?? Open the inflow ducting to the cabin heat blower to take in engine compartment air directly..?

The only downside I can think of is the loss of cooling airflow diverted from the engine cooling blower to directly cool the exhaust manifold on a HOT summer day.

Thoughts..??

[RSTarga]

exactly how would the hot air from the he get to the passenger compartment? In the older cars they only had the engine fan and you have to constantly move the center handle up and down. Porsche had a solution, the electrically operated air controller in the early 80's It basically did what you do manually.

[fanaudical]

If I understand your idea correctly, you'd do the following:

- Install the block-off plates off the fan shroud.
- The cabin blower pulls air through the heat-exchangers.
- Heat is controlled by the flapper boxes, but rather than spill heat you'd be adjusting the amount of suction from outside (under the car) versus through the heat exchangers.

Did I understand that correctly?

I see a couple of issues here:

- Potential to suck CO from exhaust seems higher to me in this situation.

- Most centrifugal air blowers (like our cabin blowers) just don't generate enough "suction" to move adequate air through the duct sizes installed in the 911. (You'd be looking at installing more of a "shop vac" style blower - with associated noise issues.)

- Loss of cooling action on the exhaust (much less air through the heat exchangers) would increase engine temps.

As an alternate idea: I think where Porsche started with a booster blower in the engine compartment was probably not too far off of ideal in this situation. If only they were able to relocate that blower somewhere outside the engine compartment to keep the motor from melting...

[gtc]

I'd crank up the heater blowers and partially close the heater valves. I think that would make it a little more consistent.

[Bob Kontak]

Originally Posted by fanaudical

but rather than spill heat you'd be adjusting the amount of suction from outside (under the car) versus through the heat exchangers.

wwest needs to respond but I am picturing the footwell blowers sucking air from the inside of the engine compartment (not from under the shroud - via mods that divorce forced air from the system), across the heat exchangers, through the flapper boxes and into the passenger compartment.

On my SC, I could see doing that pretty easily as I don't have footwell blowers but have the booster blower you mention. You could devise a plate for winter that could cut off big fan fluctuation and then remove the plate in the summer.

Also, not sure if suction would work well, vs. forced if using the flapper boxes to control heat.

[wwest]

In the factory system the engine cooling fan supplies forced airflow down, over the cylinder heats AND forced airflow into the duct to the cabin heater blower in the engine compartment. From the blower the airflow travels through the heat exchanger surrounding the exhaust manifold then to the open atmosphere and/or into the cabin.

Forgetting the blower for the moment the varying RPM of the engine results in a discomforting variation in the level of cabin heating airflow.

So why not have the blower SUCK fresh air into the duct (now disconnected from the engine cooling airflow path) and thereby supply a constant level of cabin heat independent of engine RPM?

If need be the footwell blowers could be on...or off.

[wwest]

Originally Posted by Bob Kontak

wwest needs to respond but I am picturing the cabin heating blower in the engine compartment sucking air from the inside of the engine compartment (not from under the shroud - via mods that divorce forced air from the system), across the heat exchangers, through the flapper boxes and into the passenger compartment.

On my SC, I could see doing that pretty easily as I don't have footwell blowers but have the booster blower you mention. You could devise a plate for winter that could cut off big fan fluctuation and then remove the plate in the summer.

Also, not sure if suction would work well, vs. forced if using the flapper boxes to control heat.

Mostly correct, thanks.

[NathanR]

You can always throttle back airflow with the levers, though it is a bit fiddly in stop and go traffic.

Given that my rear blower isn't working right now, deleting it is appealing. If I could get the FW blowers to work, I wonder if that would be good enough? Retain benefit of engine fan pushing air through HEs seems like a good idea, not bad...

[Autoban]

I finally got my blowers ('86 Cab) working properly (or what I think is properly). When the red levers are pulled up the FW blowers run only when I am below 15 MPH (I think it is around there). As soon when I get faster they turn off and let the engine compartment blower and engine RPM deliver the heat. I think this evens out the differences quite well. I drove the car last week in below freezing temperatures and felt pretty comfortable.

However, it will never be as smooth as modern cars with electronic climate control.

Juergen