Need driver side heat exchanger for MFI clarification.

[Shaun @ Tru6]

There are two styles as seen below. What is the difference? What the secondary box for?

[TVRLOTUSTR3]

Hi Shaun,
I have the first one on my 72T, I believe it is original. (96,000 mi)
I wondered what the hole on top of the secondary box was for?

[Rusty 356]

The extra box is for air box heat. later version for emissions I'm sure.

[NineOhOne]

The extra port sends heat directly to the MFI pump thermostat. Secondary box? Dunno.

[Fast Corners]

The upper tube (present in both pictures above) connects to the MFI thermostat. The box that surrounds the collector of the exhaust header is to provide warm air to the pre-heater-flapper box used on '72- MFI systems.

[tharbert]

+1 pre-heat flapper box....I have have it on mine. The flapper box pulls exclusively from heated air but gradually mixes in more fresh air from the engine compartment as the accelerator is depressed. I don't believe this is emissions related. Maybe an expert can elaborate.

[Shaun @ Tru6]

Thanks guys. Doesn't anyone know where the small tube goes to? My understanding now is big tube goes to the 72/73 regulator housing, but there's also the small tube on the secondary tin.

[Rusty 356]

The small tube goes from the HE to the side tin on the engine and from there another flexible hose goes to the warm up choke on the MFI pump.

[TVRLOTUSTR3]

Rusty that hose comes from the small outlet (top left) on both exchangers shown. The small hole on the secondary on my 72 has nothing going to it. I think it could be just a vent.

[tharbert]

+1 vent

[Zeke]

The heat to the warm air box has to be pressurized just like the heat to the thermostat. On the later HE there are 4 holes total, 2 inlets and 2 outlets. The second hole on the secondary box is connected to the fan in some way. If I have time, I'll open PET.

Looks to be supplied with P/N 911 106 329 00

[Rusty 356]

I'll take some pics of my 72 and post later today.

[Jim727]

It is as Fast Corners described. My '71 exchanger is, like the '69, without the secondary box.

[tharbert]

Just to be sure, we're talking about:


The PET shows Milt's P/N (P/N 911 106 329 00) as number 34.


It's odd there are no clamps in the PET for #34. #31,32,33 is a clip, nut, bolt assembly. My bone stock car has this port open to the air...no hose. Yes, the other end of that airbox leads to the thermostat.

I've noticed the open vent before and looked for "the other end" but there doesn't appear to be anyplace to attach anything. I'm very interested to see a pic of #34 in action!

[Fast Corners]

The small tube (pointed back down towards the header portion of the heat exchanger) at the top end of the heat exchanger is connected to the same sized tube that goes through the left side engine tin (between Cyl #1 & Cyl#2). These two tubes are connected by a flexible pipe (ribbed aluminum IIRC).

From this point (steel tube in the left bank engine tin) the warm air then goes to the MFI pump thermostat (see diagram posted above) via another flexible pipe (this one is aluminized cardboard that is covered by a ribbed black plastic sheath).


Hope this helps.

[Fast Corners]

Tharbert,

The hole you are pointing to in your last post is where the air for the pre-heater / flapper box comes into the warming chamber. This air is drawn up into the flabber box from the other hole on the end (near the muffler end of the HE).

[Shaun @ Tru6]

Great information, thank you all.

here's the background. I sold a pair of HE on Classifieds, the first pic shows one of them, shipped them and when they arrived, only one, the passenger was in the box. Box was sound, taped, etc. and arrived in good shape, retaped! I've put in a claim to UPS, but nothing yet, eerily similar to when I shipped 4 identical, new boxes, each with a deep 6 to Harvey Weidman and only 3 made it. the fourth was never found.

Anyway, I've been trying to find another one of these for the guy who bought them and they seem to be super rare. The second pic is one I got from a friend.

the buyer is still using the emissions flapper box so I've got to find one like the one that is missing. have one lead, waiting for a pic to confirm.

thanks again!

[Rusty 356]

Shaun, I think I have a complete setup with the configuration you are looking for. I found a set of SSI and so the others are redundant. I'm not sure what I paid for them but will look it up if you are interested and what ever I paid will sell them to you at same price.

[Shaun @ Tru6]

Originally Posted by Rusty 356

Shaun, I think I have a complete setup with the configuration you are looking for. I found a set of SSI and so the others are redundant. I'm not sure what I paid for them but will look it up if you are interested and what ever I paid will sell them to you at same price.

Thank you! Let me know what you find Rusty, much appreciated. And there's shirt in it for you too, on the house.

LMK what design you want: '56 Speedster & '70 917 T-shirts

[Grady Clay]

Late to the discussion.

The heat exchanger you are discussing is for ’73 911T (MFI), 911E , 911S and Carrera RS 2.7 only, although there may have been some installed on very late ’72. As noted above, there is a ribbed flexible aluminum tube from the outlet tube of the MFI warm air exchanger to a tube on the left tin. There were no clamps for this tube, it simply was captive between the two tubes of the exchanger and engine tin. On the engine side of this tube there is a ‘wire grill’ over the opening.

There is a ’72 only heat exchanger, not shown here, that does not get the fresh air for the MFI warm air exchanger from the engine compartment. There isn’t a flex hose and the left engine tin is as all previous MFI engines. The ‘fresh’ air for the MFI warm air exchanger comes in a shielded slot on the engine side of this exchanger. Of course this is subject to road dirt. Consequently Porsche added the tube to the cleaner engine compartment air.

Best,
Grady