Gutted Exhaust

[911-32]

I hope people will not think that this is going over old ground as I have spent a lot of time reviewing old posts on 3.2 exhaust mods and in particular gutted rear mufflers.

I have a couple of specific questions which go a little beyond the usual personal recommendations:

1. Supposing that I wanted to gut my rear muffler but thought it would end up being pretty loud - too loud (see second query in this regard). I could add a couple of baffles perhaps. 911NUT has posted that he added a couple of baffles but for the life of me I can't quite work out from the descriptions where they are placed or what they would look like. Can anyone help out with a fuller description or a picture?

2. All the track days (DEs) I run at have noise restrictions. Most around the 102db level. This is measured at 4500rpm, 1 metre form the pipe at a 45 degree angle so it is a pretty tough test. A standard 3.2 exhaust should run at around 98db and a 964 with cup bypass pipe at around 102db. Anyone want to speculate on the relative noise of a gutted rear muffler set-up? With baffles? I can run a small bolt on silencer after the rear muffler that cuts the noise back a couple or 5 dbs. What chance do I have of passing the noise test?

Looking forward to hearing your views (hopefully 911NUT can add thoughts).

Thanks,
Richard

[Bill Douglas]

Ha, I don't recomemnd this, but to pass my MOT on my old Triumph motorbike I used to shove chicken mesh up the exhaust pipes. I know there are Harley Davidson mufflers that fit inside exhaust pipes, maybe look at this as an option but performance wise, the stock or slightly modified muffer is probably better.

[911-32]

Still hoping my queries may be viewed by others. As people have done the gutted exhaust and install baffles thing, there must be some knowledge out there to help with query number 1. Perhaps the attached pic will help jog some memories.



Thanks again,
Richard

[911nut]

I gutted my exhaust by doing the following:
* Cut the stock muffler into 3 pieces with a metal cutting band saw. There are a series of arc plug welds that hold the perforated pipe/glass pack, three columns of them (as found about the circumfrence) to be exact. I cut the muffler just beyond the outside comumns toward either end.
* Cut the plug welds out of the center section and removed (more like pounded) the perf pipe and glass packing out.
* Cut the stub of the outlet pipe all the way back to the shell interior (there will be two pipes in there,inlet and outlet. Only cut the inlet).
* Traced the outline of the cross-section profile onto two 1/8 inch steel plates. Then I traced 3/4 inch circles onto the plates (the area of all of the circles is equal to the area of the inlet/outlet pipe) but I made a hole in one plate where I could weld the inlet pipe stub to when I installed the baffles (this baffle would butt up to the inlet pipe).
* Cut the holes into the baffle plates and welded the plates into the ends of the muffler. For better muffling the blind end can be stuffed with steel wool.
* Welded all 3 pieces back together and welded up the holes where all of the plug welds were.
It's LOUD but in my first attempt I didn't put any baffles in and it was really bad. Now my SC sounds like a Ferrari V-12 from an old racing documenary and everyone loves it.
It did improve performance due to the lesening of back pressure so overall I'd say it was worth it.