Unconnected exit from heat exchanger

prebordao · 09-05-2013, 07:55 AM

Yesterday, I noticed on the left side exhaust heat exchanger there's an unplugged exit.
It's near the front of it, where the 3 headers get together, pointing upwards and about 1'' dia... See diagram

What's it for ?

Neilk · 09-05-2013, 08:05 AM

MFI pre heater.

prebordao · 09-05-2013, 08:07 AM

So, no use on a CIS car ?

Neilk · 09-05-2013, 08:24 AM

oops, maybe I am wrong.. bump back to top for good answer...

prebordao · 09-05-2013, 08:25 AM

maybe you're right and they used the same part...

Anyway, can anyone confirm ?

will hung · 09-05-2013, 09:08 AM

Maybe this will make the questions and answer clearer. I'm not sure which outlet you are talking about, so I circled the 2 possibilities.

The part circled in this pic is the MFI preheater. It has zero function in a CIS equipped car, but it should be blocked off.

If this is the piece that isn't attached, get some flex pipe and attach it. Otherwise the heat is escaping the heat exchanger box, but it isn't getting to your cabin. If it is disconnected, maybe it's because the cabin was getting too hot.

prebordao · 09-05-2013, 09:10 AM

Thanks. It's the MFI pre-heater.
Have to check if it's blocked off... don't seems to

GT2BH · 06-12-2014, 09:54 AM

Sorry to revive this, but I live in a very hot country and need zero heating. Can I just disconnect this and cancel the flex pipe completely from both heat exchangers? I just need the piping for the AC.

911pcars · 06-12-2014, 10:11 AM

Quote:

Originally Posted by GT2BH

Sorry to revive this, but I live in a very hot country and need zero heating. Can I just disconnect this and cancel the flex pipe completely from both heat exchangers? I just need the piping for the AC.

Probably, since the closed heater valve dumps the hot air to atmosphere anyway.

However, you may want to direct the hot air downward rather than upward toward the chassis.

Sherwood

GT2BH · 06-12-2014, 12:03 PM

Thanks for the input - I'll see if I can use part of the exiting piping and redirect downwards

Flat6pac · 06-12-2014, 12:18 PM

You do want Air flow through the heat box keeping the engine cooler
Bruce

911pcars · 06-12-2014, 12:33 PM

Not sure if PAG designed a planned/restricted air flow volume in the air path through the heat exchanger. That would require hi-tech calcs for the era.

Why not just reconnect the hose ducts to the heater valves and leave the heater OFF? An opening in the heat exchanger air path could create an ideal catch can for road debris, water, mud, leaves, etc.

Sherwood

GT2BH · 06-12-2014, 12:53 PM

Quote:

Originally Posted by 911pcars

Not sure if PAG designed a planned/restricted air flow volume in the air path through the heat exchanger. That would require hi-tech calcs for the era.

Why not just reconnect the hose ducts to the heater valves and leave the heater OFF? An opening in the heat exchanger air path could create an ideal catch can for road debris, water, mud, leaves, etc.

Sherwood

I can possibly keep the hoses since I already ordered a set from Aircraft Spruce. I just thought the less hot pipes in the engine bay the better, plus cool air will flow in from the openings in the engine bay without the piping.

911pcars · 02:13 PM

If you have the factory '74 heating parts, consider back dating to an earlier 911 (pre '72?) system that only contains 2 cooling air hoses to the heat exchangers. That way, there's a minimum of hot air ducting on the top side of the engine compartment.

Air shroud ducts barely seen here:

Jack Stands · Jack Stands's Garage

The easiest thing would be to simply block off the opening with a plumbing type expansion plug. Otherwise, if you really don't need heat, consider selling those exchangers to someone with a MFI car and putting on headers and block off the heat tubes so more cooling air goes to the engine.

911pcars · 06-12-2014, 03:13 PM

Quote:

Originally Posted by Jack Stands

The easiest thing would be to simply block off the opening with a plumbing type expansion plug. Otherwise, if you really don't need heat, consider selling those exchangers to someone with a MFI car and putting on headers and block off the heat tubes so more cooling air goes to the engine.

Suggest not. Only if using headers (w/o heat exchanger).

Blocking the hot air inlet and/or exit openings will trap heated air inside the heat exchanger and could lead to overheating symptoms. A connection to the engine cooling air ensures adequate air flow through the HE chambers.

If you decide to give up heat, go with headers and direct all cooling air to the engine.

GT2BH · 06-12-2014, 10:26 PM

Headers sound like a great idea.. eliminate the heat exchangers..

Any idea if I need to buy a seperate cat-bypass pipe and exhaust to fit the headers if I go with Bursch headers?

911pcars · 06-13-2014, 12:41 AM

Quote:

Originally Posted by GT2BH

Headers sound like a great idea.. eliminate the heat exchangers..

Any idea if I need to buy a seperate cat-bypass pipe and exhaust to fit the headers if I go with Bursch headers?

IMHO, the cost/benefit ratio isn't very good for a new exhaust system just to delete cabin heat. It would make more sense if used along with more significant engine upgrades. Installing headers usually precludes using a cat due to space limitations, and if you're required to have periodic emissions tests, the visual would be a dead giveaway.

If you want a sportier exhaust sound, a cat bypass pipe and a sporty muffler would be a logical upgrade. There's a wide cost range from modest to significant. YMMV. Many pieces are in the Pelican store. Take a look.

Sherwood