Stembro Exhaust

[Rammer]

Originally Posted by JAAY

I think it looks like a two cherry bombs and some bad piping. I have Mille Miglia exhaust and it sounds way more tuned than that. I am only going by looks and sounds of it. That sounds like a steep price too for 2 straight through civic mufflers. If you like the look of that get a GHL.

Jaay,

are you happy with the Mille Miglia exhaust?

[Cloudsurfer]

Jayy-

Where did you acquire the Mille Miglia? How do you like it? Is it resonance free? Cost?

thanks

Patrick

[John V]

Any and all of this style exhaust will resonate. No way around it.

For 1,000 bucks, just go have a muffler shop build your own and spend the rest on gas.

[Cloudsurfer]

Well the problem I have, is that I have the GHL Race exhaust, which are basically straight pipes. Sounda AMAZING above 4k, but also resonates pretty badly between 2 and 3k. I have thought of the idea of cutting the piping and welding in some resonators or straight through silencers, but if I'm going to hack the thing up (I got it cheap enough I dont really care about sacrificing its value), I'd like to do some homework and insert the proper size and length devices to quiet the resonance from 2-3k.

Any thoughts on that?

Patrick

[John V]

You're not going to cancel the resonance (the "drone") by inserting more silencers. The straight-through glasspack-style silencers don't do anything for low frequency tones, and the resonance is caused by the low-frequency cylinder firing rate (CFR). I calculated it out to be about 110Hz.

The stock muffler uses helmholtz resonators with absorptive material plus long path length to attenuate the CFR. Any straight-through exhaust is going to resonate between 2-3k on the Boxster, period.

I do believe there are ways which you can eliminate the resonance using quarter-wave resonators and additional tailpipe length, plus reactive mufflers, but I don't have regular access to a welder nor do I have the desire to throw a bunch of money at the problem. Maybe someday.

[Cloudsurfer]

John-

Thank you for the much thought out response. So, essentially, in my situation the only thing I can do is swap out my GHL for a properly designed, non resonance exhaust (i.e. CarGraphic, FabSpeed, Gembella, etc)?

Patrick

[Cloudsurfer]

John-

Related to that, I had another thought:

Would it do anything to elimate some of the drone if I welded in some high flat cats into the exhaust section (that way I could do catless headers and secondary cat deletes and still be semi EPA friendly and have a happy ECU)? Would the cats do anything to attentuate the low frequency drone or are we still left with the same problem?

Patrick

Originally Posted by John V

You're not going to cancel the resonance (the "drone") by inserting more silencers. The straight-through glasspack-style silencers don't do anything for low frequency tones, and the resonance is caused by the low-frequency cylinder firing rate (CFR). I calculated it out to be about 110Hz.

The stock muffler uses helmholtz resonators with absorptive material plus long path length to attenuate the CFR. Any straight-through exhaust is going to resonate between 2-3k on the Boxster, period.

I do believe there are ways which you can eliminate the resonance using quarter-wave resonators and additional tailpipe length, plus reactive mufflers, but I don't have regular access to a welder nor do I have the desire to throw a bunch of money at the problem. Maybe someday.

I'd like to hear your ideas on it, and maybe I'll build it. I have all the tools necessary. You help me design it and I'll build 2; one for me and one for you What do you say? Or do you think there really isn't much power to be gained, and not worth the effort? BTW, I plan on forced induction later on...



I installed Che's exhaust and it sounds racy for sure (PM me if anyone wants to buy it before I put it up on Ebay and I'll give you the details). Just not my taste. I thought I would try it, but it's too loud for me. I like stealth. All I wanted was some more HP.

[Cloudsurfer]

Well I was hoping to get rid of my resonance by installing the FabSpeed system. It is much better, but still has resonance between 2 and 3k. I think with these cars, due to the short piping length and the cylinder firing rate.

Patrick