I have to concur with ^. Very interesting thread as it hits home w/ me. The drone on my Boxster is awful. Headers, sport cats and dual free flow mufflers minus the OEM cross over design = a very short exhaust length and terrible drone that vibrates the entire car at highway RPM's. I wear earplugs if I have to drive it for extended periods.

The headers were shiny though

 

I wanna sleep with those headers, they're so beautiful.

 

EisenHaus thinks it works for the R56.

 

Yes, k-huevo, the EisenHaus solution sure looks elegant! And it represents the Helmholtz resonator solution at its best in shiny SS. My biggest problem is calculating the length of that third pipe! The diameter is not so much a problem--the bigger the volume the more absorption of the offending frequency, however the frequency is determined by the length of the pipe. Even if we knew the length of the R56 pipe, it might not be the correct length for the R53.

I have hooked up with Juston Poole who made my CMC header (sweet!) and he is putting together a custom section for me with series cans. I'll report more when I know more...

 

Zero-Drone series cans for the R53.

 

k-h... What are those ? Thinking about doing something similar with my oneball...

 

It looks like a one-ball with a glass-pack after the center hangers?

 

Certainly *something* added both before and after the hanger... I just want to know what type, brand and sizes...

 

While I don't have any info on Helmoltz calculations or any specific engineering around exhaust system developments, I'll pass on a few things I've learned trying to quiet my turbo rotary engine.

Muffler selection makes a very big impact on overall sound - max db, tone and resonance. I have noticed a significant difference using straight through designs from Borla and Magnaflow. Both of those mufflers work very well.

The round canister style mufflers are not anywhere near as good as the traditional shaped mufflers from Borla and Magnaflow in any of the previously mentioned characteristics.

I have also recently experimented with mufflers packed with some kind of steel wool which I believe are also a straight through perforated design. They helped get rid of high frequency harshness and raspiness while also providing a net decrease in sound across the RPM range and also decreased droning compared to a perforated Magnaflow used in the same exact position.

Before embarking further, you may want to consider revisting your choice of mufflers. During my research on my own exhaust, I had pretty good luck talking to the technical guys at Magnaflow in helping me to pick the right muffler.

Cheers.

 

A note on steel wool... USE STAINLESS. This is what happens when you pack it with regular steel wool and do a dyno pull...

I wish I had the picture of the pull where this spot started glowing bright orange and then sparks of steel wool started flying out as the motor passed 10k rpm . There's some stuff called Superwool 607 that we ended up using in that muffler (once a new aluminum body was rolled up). Also, the packing has a huge influence on sound volume. We tested that muffler without packing and it was off the scale of our 125dB tester. With Superwool, it was around 108-109. Quite loud for street use but we only needed to stay under 110dB.

 

Boy this whole muffler thing is crazy. After talking with Juston for quite a while yesterday many of my thoughts have crystallized. All mufflers are not made equal, that's for sure. It seems that there is a group of manufacturers (other than the biggees-Magnaflow, Flowmaster, etc.) who make lots of mufflers via contracts and they are sold under various names, etc. Then there are the Asian muffler manufacturers that make the same 20 "sport compact" mufflers that you see on EBay and everywhere else on the 'net. While I don't want to go overboard on a muffler (I see them currently as consumables--haha) there's clearly better and worse out there. Cherry Bombs seem to fall in the worse category, while $300 Magnaflow mufflers would fall in the better category.
I've decided to put my current fate in Juston's hands and see what he comes up with. He seems to understand Minis pretty well, and exhausts even more.

 

Good luck with that Dr. Phil, and let us know what you find out?

 

Well, so far we've concluded a few things:
1. Adding length to the system will lower tone and reduce possible resonances but adds weight and defeats the whole purpose of simplifying the exhaust system in back of the Mini. Long exhaust systems don't need to worry too much about muffler type and quality (especially if it's a Ford F150!)
2. Even without a battery, there's not a lot of room under the boot. The distance between the center tunnel and the valance is 25". Long mufflers reduce noise and potential droning, but don't fit in the space if you want tips.
3. Multiple mufflers are more likely to eliminate drone, as you "mess around" with the shape of the straight exhaust pipe.
4. Big fat mufflers (like those in Jan's R53 system photo earlier in the thread) are more likely to be quieter and drone free.

That's it for now.

 

any more news on this?

 

Juston is waiting for the tip to arrive and will fabricate my exhaust next week, then ship from GA to NM. So I should be able to report on this new system in about 10+ days. Sorry that it will take so long, but trust me, no one is as impatient as me to see/hear/feel how this goes.

 

In the meantime, how bad is it really? I mean you don't have to wear earplugs of noise canceling headphones or anything that extreme do you?

 

The two straight systems I have tried suffered from such a horrendous 3000 rpm drone that I could only live with them for 2 days at most. There is not enough money on the planet to get me to suffer them any longer.

Juston is going with the "volume is the solution" solution. If all else fails I will try the Helmholtz way, but no-one seems to be able to tell me what length pipe is needed. I could always guess from the R56 Eisenhaus system.