My 911 Sport Muffler Build

JSZ · 12-09-2022, 12:00 PM

I picked this beat and battered early 911 muffler up and thought I would reimagine into a sport muffler with GT3 style outlets.
Received the muffler, someone smashed it up and tried to weld it up, poorly done. I proceeded to cut the muffler open, cut out the old damage to the skin, reweld in new metal and then work it on the english wheel to restore the shape. The inside was gutted to the sketches I made, ( with help from other sport muffler build info), and added baffle holes, cutoffs and blocks internally. The redone exterior skin was reinstalled and welded in place. Next was to build a jig for the new GT3 end placement and for the flange placement. The GT3 outlet pipes were a piece of stainless steel tubing that was welded into the muffler using the jig for alignment. The old flanges were corroded, so I cut them off and used the jig to install new flanges and fully weld them into place.
For the installation, I removed the factory valance and installed the muffler and started it, love the sound. Next was to rethink the rear valance to allow for the GT3 outlets and new metal at the former outlet on the driver side. I picked up a banged up rear valance at Carlisle last spring at the swap meet. I spent some time cleaning, blasting and straightening the metal for reuse. A few mockups were made for patterns to cut the valance. Valance was cut, new metal was wheeled for driver side former outlet and then tigged to the valance. The valance has been fit, needs a bit more planishing, then primer and paint. So far very happy with the look.
Next, I want to eliminate the US over rider bumperettes, so I am going to look for a toasted rear bumper. Tig up the holes, recess the license plate and build new recessed license plate lights. Just have to find a bumper.
Did a bit of driving before winter and was happy with the sound and throatyness of the muffler build. Not sure what it will be like on long distance freeway rides, however that is a rarity for me.
Some photos of my build to date. More will be added later.

JSZ · 12-09-2022, 12:03 PM

more photos

JSZ · 12-09-2022, 12:13 PM

a couple more

Porkshop · 12-09-2022, 12:57 PM

Nice, Back in the early 80s I worked for Midas and gutted a customers 911 muffler. After test driving I have been hooked on the 911s....

75 911s · 75 911s's Garage

Nice work. I followed the up fixin design for my 75 2 in muffler to convert to a 2in, 2 out -which is tried and true, but I do like the thread "sport muffler 2.0" and your design also looks superior in terms of internals. Well done. I look forward to seeing the recessed license plate on a stock bumper. I don't think I've seen that. You should add it to the "modified bumpers" thread once you are done.

lateapex911 · 12-10-2022, 03:46 PM

Interesting, wouyld love more reports on the sound in all conditions...

JSZ · 03-07-2023, 04:50 PM

Finished the custom rear valance for the GT3 outlets. Pretty happy with the results. I need to final blast, a bit more metal finish, epoxy, gravitas and then paint. Going to hunt for a ratty G body rear bumper at Carlyle for a bit more customization. Want to recess the license plate and recess lights a drop the bumper pads.
Jeff

Flojo · Flojo's Garage

nice, actually the mod of the rear valance got me more fascinated.
When I installed my 2in/2out I just left the valance on the shelf.
maybe I should get to it.

Ian Comerford · Ian Comerford's Garage

The valance is quite easy to make yourself with simple equipment. I bought a used valance for not much money and after measuring a bit and producing a cardboard template I cut off the right hand side curved area from the used valance and welded it onto the left hand side of the one on my car. The curvature is identical and it looks factory. Hope this makes sense.

JSZ · 03-08-2023, 02:54 AM

Flo….. that’s how I have been driving my car before winter was without the valance.
Ian, did not know about cutting the right rear curve of the valance and rotating it 180 degrees to create the left curve. May have went down that path in lieu of building the curve had I known and had access to a beat up valance.
All fun in the end.

lateapex911 · 03-08-2023, 05:31 PM

yea, yea, yea, but how does it sound!??!?!?

Bimmers4Life · 03-09-2023, 07:41 AM

Great fabrication work on the GT3 exhaust and lower rear valance.

gdp_samson · 03-09-2023, 08:00 AM

Is this all TIG welded ? or do you think with MIG it would be achievable as well ?

NotStock · 03-09-2023, 02:40 PM

Good taste in floor jacks and bench vises... and cars I guess too. Very nice work.

JSZ · 03-09-2023, 05:08 PM

Quote:

Originally Posted by gdp_samson

Is this all TIG welded ? or do you think with MIG it would be achievable as well ?

Sure this could be mig welded. It very thin gauge so you have to master the start stop technique. Problem is if you’re going to mig weld with stainless you have to weld with tri gas. You can weld stainless with steel filler however it will rust.