1st Gen R53 Cooper S Free Flowing Quiet exhaust

Wellzy, hopefully I can save you some angst - been well down that road. I've used
- a straight back (LOUD, no power, not enough restriction and some restriction is necessary to gain some torques)
- various configurations of single can and fruit loop ("two-can") systems, and one memorable 3-can system, attempting various configurations of spiral mufflers, resonators, and glasspacks, in both front and rear positions
- 2.5" and 2.25" systems

The ONLY straight-back that worked sonically on the R53 involved a 2" ID muffler (off a Justa!) just aft of the cat, an 18" 2.25" glasspack, then a small 2.25" resonator off a Buick, for a total of (3) cans, (6) muffler clamps, and a lot of cussing... and that one didn't make any power. No losses, but no power. Sounded fantastic, but then again so did the Borla, and the Borla actually made a few hp while sounding good. And it fit better.

One that *nearly* got it was a 2.25" system using the stock front piping (to retain the bend and the center muffler mount), using (2) Summit Racing 18" SS glasspacks, one just aft of the flange and one between the chassis brace and the batt box. Sounded fantastic for a couple thousand miles, a *little* drone but not bad, note that any glasspack system will eventually "blow out", and all will leave some shiny dust on the back of our llittle aerodynamic toasters. Then we tried to weld it (it had been clamped). The act of welding caused some of the packing to burn and the alignment to change, then it got droney. We made some power with that one, but I didn't want to live with it, even in the former "OK" sound, long-term.

Lessons learned:
- It's less noisy if the higher-restriction muffler is upstream so you have the necessary pressure drop across each muffler
- Straight-backs will get you pulled over.
- Single glasspacks will probably get you pulled over.
- Double glasspacks will get you "the look".
- None are what you'd call "subtle".
- Exhaust diameter near as makes nearly zero difference on our little motors with a stock pulley, just not enough airflow except at wi-ide open for a long time. Some restriction actually seems to add to torque, which is good, we like torque around town. This was a strength of the Borla.
- Aligning exhaust systems is not really easy on jackstands, alone.
- "Real" muffler shops laugh at homebrewed systems, even if they work
- Summit racing SS band clamps need grade 8 fasteners and they come with grade 5. They can break. Dramatically ("BANG-ping-ping-ping" followed by "pfff" and, if left long enough, "waaaah")

For drone: As far as we can determine (using some solid engineering, good maths, and lots of practical experience), it's the length of the pipe as compared to the interior volume of the car and the resonant frequency of the chassis, meaning the R56 exhaust (which you can probably run if you cut off the battery box and fab up a center mount) would likely do the same thing. It seems EVERYTHING comes together ri-ight about 3000RPM at that pipe length, regardless of diameter (2.25" and 2.5" both do it, at very slightly different rev ranges but it's all at 70MPH +/- 5). It seems this *can* be addressed using a Heimholz Resonator, a specific length of capped exhaust pipe, welded at a "T" to the rest of the system, angled to drain, and of a length determined by which frequency you want to moderate. It's all very mathy, but it works - problem is, by then, you've thrown so much into it that a factory system starts looking like the Holy Grail.

Oh - as for testing, we used a full 2nd gear "pull" on a long, essentially empty onramp near the house. Not perfect, but with some maths it was directionally "good enough".

Hope that helps!

 

Have you tried parking it? That should resolve your drone issue.

 

Thanks for this, and your previous posts. You have saved me a ton of time and money. I'll stick with split cans, thank you....

 

Dixon, thanks for the info it is very useful. I knew going to in to the it was going to be a tuff row to how. But I want to run diffuser tunnels and have limited time before the dragon. I may try one more version before then if I have time. Cutting and weld are not a big deal to me. That said this summer when I have more time I will make a twin can set up that will work with the diffuse. I also just found out that a good buddy at work know the owner of Stainless Works Performance Exhaust, Headers and Fabrication so I will be picking his brain.

 

This, I think, is the answer. Let us know what you come up with.

 

We have full confidence in you to find something else that'll take it's place.:devil:

 

Did someone say stupid? I am here! :lol:

 

With having rework my batter box and the way the difuser set I should have room to do something. The biggest problem is finding mufflers that will fit. We shall see what I come up with.

 

Coast fab, if money is no object. They can make them custom, and they have the advantage of being able to be easily repacked. Jan packed some with Kevlar; it doesn't blow out like glass.