are headers interchangeable? 3.0,3.2,3.4

[mack6820]

I'm wondering if headers are interchangeable between the engines. Someone mentioned he had 993 headers on a 3.0 I think. What would be the best for a 3.0 with heat?
Thanks in advance!
Mack

[Bill Verburg]

yes, w/ a few caveats
993 right side collectors have a bolt pattern that is rotated 90* from all previous designs, but idf you cut the welds and rotate the ends they are interchangeable.

Some designs used different oil routing schemes

some designs can interfere w/ the clutch helper spring.

[mack6820]

oh, ok, so the overall distance and dimensions for the exhaust ports are all the same? except for the 3.4. So will a 3.2 header fit on a 3.0?

Dont know why but Ive noticed they are cheaper to buy.

[tonythetarga]

interchangable doesn't also mean that the header diameter is optimal for each of those motors. The 1.5" might be right for the 3.0 and the 1 3/4 diameter might be right for the 3.2. You might need to supply a few more details. All headers do not deliver increased hp results (when you put too big a pipe on too small a motor or vice versa).

[Bill Verburg]

Originally Posted by mack6820

oh, ok, so the overall distance and dimensions for the exhaust ports are all the same? except for the 3.4. So will a 3.2 header fit on a 3.0?

Dont know why but Ive noticed they are cheaper to buy.

From 2 thru 3.8 the spacing is the same

yes, a 3.2 header will fit on a 3.0 again a caveat, early 3.0s used thin flange manifolds w/ short studs, from ~'78 up they all used thick flange manifolds w/ long studs. You can change studs or use washers to accomodate.

[SpeedracerIndy]

I'm reviving this thread because I currently have my engine out and am looking for some used heat exchangers. My 81 SC (ROW) has the thin flange exchangers. If I swap out all of the studs for longer, can I put thick flange exchangers on it? I have heard that there is a lip on the thick flange exchangers that will interfere with the exhaust port in the heads on my SC.

Good thin flange exchangers appear to be hard to come by, so I'd like to try to use the thick flange ones.

[Bill Verburg]

Originally Posted by SpeedracerIndy

I'm reviving this thread because I currently have my engine out and am looking for some used heat exchangers. My 81 SC (ROW) has the thin flange exchangers. If I swap out all of the studs for longer, can I put thick flange exchangers on it? I have heard that there is a lip on the thick flange exchangers that will interfere with the exhaust port in the heads on my SC.

Good thin flange exchangers appear to be hard to come by, so I'd like to try to use the thick flange ones.

Yes, there is a lip, if it's an issue it can be removed.

You can see it here,

[Head416]

Hijack (...but I think he got his answer, so I'll be able to sleep tonight)

Originally Posted by tonythetarga

interchangable doesn't also mean that the header diameter is optimal for each of those motors. The 1.5" might be right for the 3.0 and the 1 3/4 diameter might be right for the 3.2. You might need to supply a few more details. All headers do not deliver increased hp results (when you put too big a pipe on too small a motor or vice versa).

Can anybody tell me where exactly is the 1.5" dimension? (Talking 3.0 here.) Is this the ID at the flange, right at the opening where it connects to the heads? Or is this the diameter a couple inches into the tubing itself at the inlet side? Or are they the same?

To state another way: For a 3.0, does the ID increase at the flange to 1.5"? Or is it a consistent 1.5" ID?

Is the tubing a 1.35" ID by any chance? (Am I making any sense? )

Thanks.

[Bill Verburg]

Originally Posted by Head416

....Can anybody tell me where exactly is the 1.5" dimension? (Talking 3.0 here.) Is this the ID at the flange, right at the opening where it connects to the heads? Or is this the diameter a couple inches into the tubing itself at the inlet side? Or are they the same?

To state another way: For a 3.0, does the ID increase at the flange to 1.5"? Or is it a consistent 1.5" ID?

Is the tubing a 1.35" ID by any chance? (Am I making any sense? )

Thanks.

The primary pipes are 1.5" OD, If my memory is any good that's 1 3/8" ID(I can get the exact measurements when i can get to my main computer). The collector is bigger, again do't have the dims on this laptop.

[Head416]

Bill, you are exactly who I was hoping to hear from... thanks for your help!

So... can I conclude that I can grab any early exhaust (say '69-'74) and bolt it on?

I'm basing that on the following:

- I have a RoW '81 911SC, therefore thin flange
- My O2 sensor is disconnected, so the bung doesn't matter
- ID of 1-3/8" tubing for a 3.0 seems to match

Am I missing anything important here?

Thanks again.

[Bill Verburg]

Originally Posted by Head416

Bill, you are exactly who I was hoping to hear from... thanks for your help!

So... can I conclude that I can grab any early exhaust (say '69-'74) and bolt it on?

I'm basing that on the following:

- I have a RoW '81 911SC, therefore thin flange
- My O2 sensor is disconnected, so the bung doesn't matter
- ID of 1-3/8" tubing for a 3.0 seems to match

Am I missing anything important here?

Thanks again.

The SSI's that most are using today are slightly different is design and materials from the oem '69-74 header/heater boxes.

The modern SSI is much superior in design and materials.

That said, yes, you can use any of the '69-74 oem header/heater boxes on a 3 liter. The biggest concern is corrosion that would allow exhaust gas(CO) to leak into the cabin heat supply. The earliest oem header/heater boxes were not ss and would rot allowing this dangerous condition to develop, as the years wore on, better materials were used, toward the end approaching SSI for quality but never quite getting there.

[Head416]

Does anybody know if there was a version that had a 1.35" inner diameter? I'm talking to a guy about buying his and he measured the ID as 1.35" (not at the flange, but down into the tube a little).

1 3/8" = 1.375"... seems awfully close to 1.35", but I don't want to "upgrade" to smaller tubes.

Thanks again.