Heat Exchangers Insides

[Jay Laifman]

I am curious about what is inside of the stock 911 heat exchangers. I tried to find a cutaway picture but couldn't. I assume that each cylinder pipe stays separate and flows around to the other side where they merge. Are they equal length? When someone wants to do performance headers and not run heat, what "improvements" do they make to stock? Longer or shorter lengths before the merging? Larger ID? If using larger ID pipes, do people also make the head exhaust port larger?

I know in the 356/912 world, many attempts to improve on factory don't work, or if they do it's only at high rpm, with a corresponding loss of power at low end. That is, the factory already found the sweet spot. Is that the same for the 911?

[Jon B]

I am curious about what is inside of the stock 911 heat exchangers. I tried to find a cutaway picture but couldn't...

Jay, here's what they look like with the shrouding removed.
The factory referred to this as "equal length".



I'll let others with more time answer your performance and improvements questions... :-)

Jon B.
Vista, CA

[gled49]

The factory heat exchangers 1-2-3 side were equal length. The 4-5-6 side was close. I knew John Daniels pretty well and when he made his SSI heat exchangers he moved one pipe in the 4-5-6 side to equal them, having to eliminate one of the exhaust nut tubes, from 3 to 2.

[TheTorch]

Always wondered why my thick flange SSIs had 2 barrel nuts on one side unlike others I have seen. I learn something here every day.

[Jay Laifman]

Agreed! I would assume though, or at least hope, that the factory didn't arbitrarily pick a different length - but specifically tuned it for engine pulses to match appropriate.

[gled49]

I suggest, form follows function, and they adjusted pipe length to facilitate heat exchange installation. John wanted equal length and figured out how to do it.