Thinking about modifying my spare muffler.
 

I have a spare single in single out factory muffler hanging in the rafters. I am thinking about adding a second outlet. Any pointers?
Do I just cut a hole symetrical to the outlet already there and weld on a new tip? Or do I need to do some internal mods?

Another thought is a "period correct mod" cap off the tip that is there and put two outlets in the center for that early car sport pipe look?

Any guidance?http://www.pelicanparts.com/support/smileys/2ar15.gif Duels are cool!

Had my stock muffler done and it appears that they just cut and welded. makes the car a bit louder, no real noticable h.p. gains--looks realy cool though. Just bought SSi's and a dual in dual out.

Modified 911 Muffler (Pre-1974)
 

A link on the 911T Registry page on how to modify your muffler.

http://www.911t.org/WklyReprint/modified_muffler.htm

Shawn, I did this mod awhile back and I'm pretty pleased with the out come. As for the mod adding performance well, i did notice very small increased output in my lower 3000 rpm range, but the sound is clean and deep with no rasp at all.
With my mod I incorporated 3-1/2" tips which gives it a nice look.
As for internal modifications if you decide on twin center outlets you will have to open the muffler up and perform modifications to internal baffles, but if you go with the plain addition of a second outlet on the opposite end I really don't see a need for internal mods. Just my own persomal observation. One thing I did perform on the second outlet was, After boring the hole I reinforced the shell and added tuning capabilities by the use of a threaded flange that lends itself to having 1-1/2" nipples installed to achieve desired tonation.


Jorgre (Targa Dude):cool:

I looked at the link at the 911T site. Do the same internal mods need done to a single in single out? I assume the document is for a dual in single out?
I am hoping I don't have to split the thing open. If I have to go to all that trouble I will leave it hang.

Jorgre,
Please explain this "tonation" mod?

That's a good question, unfortunately I can't answer it.. I would venture to guess that with a single in single out muffler since the inlet and outlet are on the same side it would probably be same case senario..as adding the second out let to the opposite side.. but if you are planning on the twin center look..I would guess the muffler would have to be opened up and modified. JMO

Jorge (Targa Dude)

Well, just like you Shawn before I performed this modification I posed the same question to the board as you are doing right now.
What I found at that time was, in order to achieve equal tonation it was recomended to start out drilling a hole about the size of a quater and then progressively increase the size till proper tonation was achieved.
That seemed to be allot of extra work and besides it would also make it difficult to perform if the second tip was to be welded in place.
So I decided to go with a much larger hole and have the capability to fine tune the muffler with the tips welded inplace.

Jorge (Targa Dude)

I am doing whatever is easiest. If I can just add a second tip on the oppisite side that is what I will do. I am not going to split the muffler and do any mods internally. Not worth my time. Please explain what you did to add a second tip on yours.

Shawn, if you want I can send you some 3d solid models of my mods. Unfortunately I'm at work so if you want I can send them to you later tonight. it's really not that difficult of a mod. but it may also depend on what size of tips you want to run.
and you have to concider also modifying your rear valance as well.


Jorge (Targa Dude):cool:

Thanks that would be great!
I dont have my new rear bumper yet so modding the thing is gonna have to be done when it gets here anyway.

Hey Shawn, I sent you that file. I hope your email is up to date. let me know if you have anymore questions... and good luck..


Jorge (Targa Dude):cool:

I got it. Thanks. I am going to PM you. We need to talk about this tonation thing. I think I get it but I have some questions.

I also did this modification. Well worth the effort IMO.

I did not do any modifications internally. The hardest part was fabricating and exact (Opposite) duplicate of the original taill pipe. I used two mandrel bent pieces of SS pipe and welded them together to get the proper look and fit. I wonder if anyone sell this pipe for the modification. I also remember an article in Excellence that dynoed all kinds of HP projects...including chips, headers, mufflers etc. The two outlet exhaust modification resulted in one of the best gains in the test. I'll try to dig the article up and post.

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