DIY early sport muffler

[jpnovak]

A few weeks ago I asked about building a sport muffler. The diagram for converting a sausage muffler to a sport can be found here.

DIY sport muffler - Can someone repost pics?

After sourcing a tired 2in/1out muffler and a section of pipe I got out the plasma cutter, cutting wheels and welder. Here is my play by play.

First cut the top out of the muffler usnig the cut-off wheel in the grinder. This was not in the diagram but its the easiest way to make the two inner perferations.



Oh, here is what the inside of the muffler looks like before you cut the holes.



I managed to miss the pictures of the holes I cut. Its fairly easy to describe. I cut a 2.5" diameter hole in the left stop panel. When you look at the panel that separates the upper and lower chamber you will see a round section that mimics the cut-out in the diagram. I cut as far forward as I could get and then followed the indentation.

Next, cut the outlet off. I cut just inside the weld bead.


I then got the section of pipe and notched the end.

Then trace this end on the back of the mufler. I put them about 1 inch to the right of the muffler bands.

[jpnovak]

Next cut the holes and insert the new outlet pipes.




next, get out the welder and start putting it all back together. I ran out of welding gas while stiching the cover back on. it will have to wait a bit before its on the car.




This whole process took about 1.5 hours including welder setup and cleanup. Its fairly simple.

[Zeke]

Good deal, Jamie! We need more explorers like you.

Now, how's it sound?

[jpnovak]

I don't know I have plans this evening and had to stop playing in the garage. It didn't get installed.

OH yeah, If you ahve the muffler the cost of conversion was $6 for a 6' section of fence post. It was cheaper than muffler tubing and very easy to weld one you grind off the Zinc coating. Once I get it all cleaned up It will receive a nice coating of High temp BBQ black.

[Alan Cottrill]

I had always wondered how to cut the holes inside the muffler. I had imagined cutting a hole for the drivers side exhaust tip then putting the torch through that hole to cut the hole in the bottom plate then putting the torch through that hole and cutting the side plate. the thing that always bothered me about this plan was leaving the metal floating around inside the muffler.

Nice work!

[al lkosmal]

Jamie,
Nice work. I'm glad that old muffler was put to good use.

Al

[Jeff Higgins]

Pretty cool, Jamie. I remember seeing this diagram several months ago. I was kind of confused then, and I'm still confused now. It looks like the original muffler had a rather large lower chamber that was open to both inlets. From there, the gasses travel through the perforated divider into the small upper chamber, through the transfer pipe into the far right chamber, then all the way out the left end and the tail pipe. I'm not sure what either the slotted pipe section or the perforated pipe in the end chamber do; they appear to dump gasses into sealed chambers. So now with the modified muffler, it appears as though the new exhaust outlets share that big open lower chamber with the inlets. That seems like it would render cutting the two additional inner holes superflous. As a matter of fact, it looks like all of the internal baffling is bypassed. Am I missing something really obvious in the drawings, or are there some baffles that are different in the muffler than shown on the drawings? It looks like you only opened up the one chamber, so could you tell what it looked like inside beyond that? It looks like this thing really isn't much of a muffler any more. When you get a chance to run it, let us know how loud it is. I really want to do this on mine, but not if it winds up sounding like no muffler at all. Oh, and good work by the way - you have inspired me to give it a try, if it's not too loud.

[jpnovak]

Jeff, you are right in that the inlets dump into the large lower chamber and now exit through the new outlets thus closing off the upper chambers. I think making the holes in the baffles increases the volume that the sound waves build up in. It likely cuts down on the noise the exits the rear making it quieter. More volume equals more chance for cancellation at resonant frequencies. Best answer I can think of.

[Jim Richards]

Cool stuff, Jamie! Loudness and impact on MFI performance are things that make me hold off on doing this for now. Well, also the lack of a plasma cutter and welding equipment.

Can't wait to hear back from you on how it sounds.

Anyone perform this experiment on an MFI car? Any flat spot?

[jpnovak]

I am sure you could get Kurt to make you one. He has the necessary skills and tools.

I can't wait to hear it too. dtw has one on his MFI hotrod 2.4. I did not notice any flat spot when I drove it. Of course, I didn't have a lot of seat time either.

[jpnovak]

I had time to complete the muffler today. I also had a short test drive.

I finished welding, smoothed them a bit and gave it a bit of my favorite BBQ black paint. Here is the newly converted muffler next to the stainless one it replaced.



next I bolted it to the car. Camera angle makes them look crooked. They are straight.



I started the car and noticed an immediate difference. There is a low rumble at acceleration that is not much different to a V8. The rumble is there with throttle blips as the fuel pressure equalizes in the webers. On the test drive It sounds no different than before. I noticed that the sound was quite calm at idle except when that SUV chrome bumper was a little close. The sound inside the car was quite normal... until about 5500rpm. The unmistakeable wail is awesome! I think its a keeper.

If anyone wants theirs converted let me know. We can talk!

[silverc4s]

Jamie,
Nice job!! That muffler looks like just the ticket for your RS. Bet it sounds a lot better now...

[atlporsche]

I did one like this for Elombard...it sounds so awesome...way better than before.

sjd

[sprbxr]

Anyone do it to an SC with CIS? I did it to my 70 2.7RS replica. It sounded great. I was wondering if there would be any ill effects on a CIS car. My SC has SSI headers and a 2 in-1 out muffler at the moment.

[cool5]

Jamie,
Looks great, I did the same thing for my 66, the sound is very throaty and especially loud when you really get on it. Did you have any problem getting the exhaust outlets to fit under the rear license panel. I test fit mine while I was cutting the holes for the pipes, and to make it fit the outlets had to be pretty much flush w/ the bottom of the muffler.

Matt

[Andras Nagy]

I replaced my stock muffler, in fact the entire exhaust system, with SSi heat exchangers, and then bought a sport muffler from Alan Johnson. Have used it for over 20 years now, and I love it, though the wifie thinks it's too loud, expecially when starting up in the garage.

On the track, as we leave the pits, the sound in first and second gear is great, sounds very "rippy" or "throaty"; the sound is almost akin to the early 2.4 sounds.

[andycook]

Has anyone converted a two in one out muffler to a two in two out system? I want to add an outlet on the passenger side of my SC. It has a 74 2.7 in it.

[jpnovak]

Andy, the second right side outlet has been done. you have to be careful. All of the chambers dump to the right side of the muffler. you can get a very unbalanced sound. Most people drill a much smaller outlet hole and then have a larger outlet pipe. the archives will have more info than I have given.

[andycook]

Thanks Jamie, I tried a search but couldn't get anything on it. Probably using the wrong criteria. SO what you are saying is cut like a 1" hole on the right side and use the larger pipe for the aesthetic look?
I have also seen where someone, again cannot find the post, fabricated two flanges and connected two 12" mufflers directly to the manifolds and built their tailpipes from there. Still thinking about that too. I just cannot swing the $$$ for a factory unit at this point, but want the sound.

[jpnovak]

this looks like a good thread for you.

Gutting stock muffler