Heat exchangers for MFI vs CIS? Is there a difference?

Shakenbake · 06-10-2002, 07:44 AM

"Two used Heat Exchangers for Porsche with Bosch Mechanical Fuel Injection (MFI). These Heat Exchangers are from a 1972 911T and work great! They will fit any 911 with MFI from 1969-73."

They look identical to the heat exchangers on my 1974 911 (cept mine are rusted through)

silverc4s · silverc4s's Garage

There is a heat riser outlet on the SSI's that is required for the MFI to function properly. I believe that these could also work on your car if you blocked off the small outlet for the MFI connection.
I am sure someone else will add a correction if I am mistaken.
The bottom line - I think these would be useable on a CIS car.

Ron,K · 06-10-2002, 07:54 AM

Chris,

I think the only difference is the MFI exchangers have a fitting on the drivers side near the flapper valve for the a hose that supplies the hot air theremostat on the injection pump. On a non-MFI engine, you could just block of this fitting.

Early_S_Man · 06-10-2002, 07:59 AM

Chris ... two differences, one significant ... on the left heat exchanger ...

There is a small bit of extra tin and a grille for the pre-heated air filter inlet on the '72 thru '76 MFI engines, and it can be ignored or cut off for a CIS engine.

There is a 25 mm outlet, high ... up near the outlet to the flapper box, facing rearward ... that provided pressurized hot air to the MFI injection pump thermostat ... will need to be capped or plugged for CIS installation.

Shakenbake · 06-10-2002, 08:02 AM

You guys are GREAT! Fast too!

Ron,K · 06-10-2002, 08:20 AM

Chris,

If you get the exchangers, I'm trying to find the "extra tin" Warren is refering to. I've installed SSI's, and they don't have this shroud. Since you wouldn't need it for the CIS, I'd be interested in buying it, assuming it can be removed without damaging the exchanger or shroud.

pbs911 · pbs911's Garage

Those are the type of early heat exchangers I put on my 78SC. I didn't know what it was for so just ignored it. Ignorance is bliss. I don't know how you would remover any extra tin without destroying the heat exchanger.

Shakenbake · 06-10-2002, 04:57 PM

Ron K, If I get them I'd be glad to let you have the cut off piece. Here is a picture of the exchangers. Trying to get a ballpark figure of what they are worth. Current bid on ebay is $250.00

Early_S_Man · 06-10-2002, 05:07 PM

Chris,

The intake preheater tin has already been removed for the bottom heat exchanger, but the 25 mm outlet is still there to be capped!

Ron,K · 06-10-2002, 05:18 PM

Chris,

Warren beat me to it, the shroud has already been removed. I do appreciate the offer though.

Ron

Shakenbake · 06-10-2002, 05:21 PM

What would top price be for exchangers in this condition?

pbs911 · pbs911's Garage

Quote:

Originally posted by Shakenbake
What would top price be for exchangers in this condition?

I paid $250 with a muffler. All in excellent condition.

Superman · 06-10-2002, 09:34 PM

I just put a set of pre-'74 heat exchangers on mine. I cut the extra heater box off too, and I plugged the 25mm line with a plastic plug, perfect size. They work great. Two things: I just noticed that part of the sheet metal seam needed to be pushed back away from the horseshoe spring a tiny bit (in case you have the 915 tranny). Also, I was noticing in my lavatory reading that one of Pelican's competitors lists the '74 hose to the flapper box as different from earlier models. So, perhaps the height of the sheet metal cone is different. No biggie.

Jandrews · 07-05-2002, 04:05 PM

I have another question on these MFI heat exchangers.

I am running MFI, but I am not using the pre-heated air filter inlet. My "extra tin" seams to have released from its welds and is sort of sliding freely on the three tubes.

Can I just cut that extra tin off? The large outlet on mine is just capped off and I do not even have the flapper box attached to my air filter housing. It is my understanding that the pre-heated air filter inlet is for emission purposes only.

On the other hand, I am well aware of the importance of the 25mm tube and hoses that feed the MFI thermostat. That I
would obviously keep.

Thanks,