What is the difference between 65-73 and 75-77 mufflers?

[tornik550]

I know this is a simple question however I wasn't able to find the answer- what is the difference between 65-73 and 74-77 mufflers?

[Bill Verburg]

Originally Posted by tornik550

I know this is a simple question however I wasn't able to find the answer- what is the difference between 65-73 and 74-77 mufflers?

'65-73 have dual inlet mufflers and single drivers side outlet, as does '74 but I seem to recall the outlet being slightly different from the earlier versions
'74-89 are all single inlet on the drivers side and the same outlet as was used in '74

[tornik550]

Ok- next question
Do all duel inlet 911 mufflers have the same width between the inlets?

[jpnovak]

Yes. Factory 2-in mufflers have the same inlet spacing.

The difference between the 73-earlier and 74 is the angle of the outlet. It changed to have a more downward initial angle and then flattens out backwards to clear the rear impact bumper. The bumper changed in 73.

[zedsn]

My 77 911S muffler is 2 in 1 out and has a sniffer tube welded with a cap for testing purposes

[frankc]

Originally Posted by zedsn

My 77 911S muffler is 2 in 1 out and has a sniffer tube welded with a cap for testing purposes

Yes, the '77 911s with Thermal Reactors had a 2 in 1 out muffler, similar to the '74 muffler, except that they had additional pipe for the EGR system that was routed to the CIS intake.

[911pcar]

A more important question is the difference internally. Anyone know?

Sherwood

[unclebilly]

The difference is this...

The bumpers are lower on the 74 on cars than the 73 and earlier cars. A early muffler needs to have the outlet tweaked down about and inch to clear the impact bumper.

Both are dual in, single out.

Been there, done that.