77 911 Exhaust Backdate

[Black77USS]

I want to backdate the exhaust on my 77. I purchased a nice set of 72-73 MFI heat exchangers a while back. Do I need to remove the shield on the one side and plug the hole/pipe above it if I use it? Would it work just fine if I leave it as is? I hate to change a good MFI unit if someone needs it and has one to swap for this one, but I don't know if anyone would be interested?!!?!?

[Black77USS]

Anyone know?!!?!?!?!

[kach22i]

Originally Posted by Black77USS

1. I want to backdate the exhaust on my 77.

2. I purchased a nice set of 72-73 MFI heat exchangers a while back.

3. Do I need to remove the shield on the one side and plug the hole/pipe above it if I use it?

4. Would it work just fine if I leave it as is?

5. I hate to change a good MFI unit if someone needs it and has one to swap for this one, but I don't know if anyone would be interested?!!?!?

You have a lot of thoughts there, I added numbers to help sort it out.

RE #1, I don't know if you can swap MFI with CSI heat exchangers, will these even fit? Are they the so-called "thick flange" I understand the 1977 needs?

RE #3, looks like part of the shield on the upper exchanger is missing or gone, is this correct? Were these ever symmetrical?

Looks like some years don't have this shield at all.
Engine Conversion 3.6L > Porsche 911 Chassis Package Parts And Accessories For Porsche Distributed By Patrick Motorsports


RE #3, I don't know what that shield and hole are supposed to do, maybe somebody else will chime in.

How does the original thermal reactor play into all of this, or is it long gone?

[Bill Verburg]

Originally Posted by Black77USS

I want to backdate the exhaust on my 77. I purchased a nice set of 72-73 MFI heat exchangers a while back. Do I need to remove the shield on the one side and plug the hole/pipe above it if I use it? Would it work just fine if I leave it as is? I hate to change a good MFI unit if someone needs it and has one to swap for this one, but I don't know if anyone would be interested?!!?!?

The only reason to remove the MFI heat stove is if it interferes w/ anything on your engine, I doubt that it will but do a trial fit or if you want to save the last oz of weight.

It would be a good idea to plug the heat riser hole but probably not essential, it would tend to create an isolated hot spot above it.

'77 will use the same thin flange as a '72/73

[Black77USS]

Originally Posted by Bill Verburg

The only reason to remove the MFI heat stove is if it interferes w/ anything on your engine, I doubt that it will but do a trial fit or if you want to save the last oz of weight.

It would be a good idea to plug the heat riser hole but probably not essential, it would tend to create an isolated hot spot above it.

'77 will use the same thin flange as a '72/73

Thanks Bill! I was thinking along the same lines, and you seem to agree? Weight is not a problem with me, and the hot spot comment makes sense. I was thinking removing the MFI heat stove (now that I know the correct terminology) would clean up the engine even if it does not interfere with anything. My only concern was destroying a good MFI unit if there is an alternative. RB

[Bill Verburg]

Originally Posted by Black77USS

Thanks Bill! I was thinking along the same lines, and you seem to agree? Weight is not a problem with me, and the hot spot comment makes sense. I was thinking removing the MFI heat stove (now that I know the correct terminology) would clean up the engine even if it does not interfere with anything. My only concern was destroying a good MFI unit if there is an alternative. RB

It does seem a shame to to modify these but if you have no use for the MFI stove you are almost forced into it.

[kach22i]

Originally Posted by Bill Verburg

'77 will use the same thin flange as a '72/73

Porsche 911 & Carrera Exhaust Pipes - Page 2

SSI Heat Exchanger Set (pair), thick flange WITH O2 sensor socket, 911 (Late 1976-77 Thermal Reactor Cars), 911SC (1980-83 USA)

Bill, will both thin and thick work on a 1977 911S, I assuming the stock 2.7L CIS.

[Bill Verburg]

Originally Posted by kach22i

Porsche 911 & Carrera Exhaust Pipes - Page 2


Bill, will both thin and thick work on a 1977 911S, I assuming the stock 2.7L CIS.

yes, the only difference on those is the length of the studs which probably have to be replaced anyway, thin flange uses the early short 20-23mm studs, thick flange uses the later 30mm studs, the longer ones were supposed to have been used only on 3.2s but as w/ many things some late SCs may have had the longer studs too

[kach22i]

Thanks.

[Black77USS]

I removed the heat stove and the heat riser tube and closed the hole. Thanks for your input on this. RB