1972 911T Heat Exchanger Question

[LeeD]

I am in the process of replacing my heat exchangers on my 1972 911 T with MFI. I am planning on going with SSI 91 913 and had a question about the preheat connector on the heat exchanger. Circled in RED in the attached picture.

Is it best to have it cut off and if I cut it off, will I need to block it off? Or should it just get blocked off? What would be the best way get it cut off and blocked or just blocked?

[buster73]

If you are running MFI why not just connect the preheater hose to the MFI pump ? Was designed like this for a reason and will help to control mixture when starting a cold engine.

[LeeD]

Thank you for your feedback. The port circled in red is not on my current heat exchanger. I do have the two ports circled in green (Picture) connected to the preheater system as outlined online and in the service manual (I am not seeing this port in the service manual btw). Do you have a diagram or picture where the port circle in red goes? Pelican and the other Porsche parts suppliers reference that a port may need to be removed or blocked, I was assuming that it was for this port.

[Flat6pac]

If you’re not going to use it, don’t be concerned with it, being in place nothing is bothered.
Lots were removed from the intake because of the road dirt getting in the air filter.
In the day, it was considered the street sweeper
The tap to the left was a hose going through the left sheet metal and into the injection pump thermostat.
The hose connect to the right goes through to the flapper box intake
Bruce

[buster73]

The red port would connect to the air filter regulator housing port as shown in your picture above. This was 72 and 73 MFI only. If you are not using it, I would just leave it alone.

[47silver]

I think that the red port is not connected to anything. It allows air to flow up to the thermostat flapper thst connects to the filter intake.
So leave it alone if you have an mfi car.

[porschedude996]

Originally Posted by LeeD

Thank you for your feedback. The port circled in red is not on my current heat exchanger. I do have the two ports circled in green (Picture) connected to the preheater system as outlined online and in the service manual (I am not seeing this port in the service manual btw). Do you have a diagram or picture where the port circle in red goes? Pelican and the other Porsche parts suppliers reference that a port may need to be removed or blocked, I was assuming that it was for this port.

I had a ‘72 911T years ago. Since my ownership was prior to Kalifornia Emission testing requirements changing, “No testing required for 1975 YM and older”, I tried and failed the test (emissions output high). I contacted a German gentlemen in South San Francisco about testing my MFI Pump and Injectors. He tested prior to disassembly and all was good. He did disassemble and reseal the pump. We spoke about my emissionss testing and brought up the hot-air hose to the pump from the heat exchanger. He stated there were two line, one within the other to heat the Bevlil washers that push and pull on the pump rack to trim fuel conditiones. I added the second line and everything passed.

Items 28-29.

[47silver]

Green small connection is connected to the paper hose that connects to the mfi pump thermostst.
The red circled port is not connected to anything it is required as it allows the engine vacuum to pull air across the heat exchanger into the filter thermostat via the large green port.

Again nothing gets connected to the small red port.
The small green port hose is called a steam hose for reasons unknown to me

[porschedude996]

Huh, it’s been a lot of years since my 911T, but I don’t remember the open pipe.

[47silver]

see this thread they call that pipe the street sweeper because it is open and can suck in dirt.

https://forums.pelicanparts.com/porsche-911-technical-forum/993030-1972-911t-mfi-heat-exchanger-hoses.html

[gled49]

Lee, I showed u the new side sheet metal in ESR, your pre-heat exchanger connects with a foil hose to the new side engine tin to bring in clean air.

[47silver]

was this tin added as at technical bulletin in 73 and recommended for mfi cars?
i was unaware or that.

[gled49]

That pix is from the RS Book, the change was made in January 23,1973 for the RS. look in your parts books for the change, sometimes accompanied by a vin or engine number, when the change occurred. All new heat exchangers come with the modified pre-heat path.