I have a full FM setup from the manifold back. It's a 2.5 exhaust with a cat and muffler... It gets a bit loud and droney on the highway and is louder than I thought it would be.

Any advice to get it to quieten down a bit? I figured this was a good thread to ask in.

Summary from this thread:

1) Magnaflow muffler is the quietest muffler. Replacing current muffler with magnaflow will probably fix the issue by itself. Not really much point in doing anything else until the offending non-compliant muffler issue has been remedied. EO2K's dual flow magnaflow is even quieter than the ones most people use. Part number is in this thread, I think page 2. Look for a ton of pictures.
2) If still too loud, adding the biggest resonator you can fit will also help.
3) If still too loud, adding 2 of the biggest resonators you can fit will further help.
4) Failing that, a spring loaded flapper valve will make a significant difference with very little pressure loss (pressure loss will depend on the spring constant, so if building one yourself, keep that in mind). Jason ripped one out of a dynomax VT that worked well. I think it would be easy to make one if you have any welding and machining skilz. Can also look into the Apexi exhaust control valve; 18PSI used one with good results.
5) 1/4 wave resonator will also help at specific frequencies with zero pressure loss. While effective, it might be tricky to fit one under a Miata, especially with 2 resonators and a big ass magnaflow.

Data point: Cameron's 3" almost-straight-pipe with a resonator is louder than what you're looking for, but still really quiet considering everything.

Also: That poor SR20 turbo feels pretty cool at 17psi.

Haha, I'm glad you guys got it working!

Thanks for the data point; one thing I've learned from this investigation is that people's definition of "very quiet" varies wildly. I'm hoping the 2 ultra quiets and magnaflow will be good enough for me.

The MKTurbo kit is very "quiet," but basically all it makes is "low frequency noise." If those added mufflers can dampen the low frequencies you will be golden.

I first got an FM 2.5" way back and found it too loud. I sold it and had a whole custom system built.
I suggest selling the muffler section and building a replacement with the big Magnaflow as a first step.

Yeah honestly... I'm pretty surprised at how loud it is. I keep thinking that I have an exhaust leak. I don't mind the revs on the highway, but it's getting annoying now.

I have a cat as well, which should have quietened things down as well.

Thanks for the input.

This is what I'm hoping for... :noes:

Update: MK Turbo successfully fit 2 vibrant ultra-quiet resonators and the big magnaflow muffler. The result is the most nearly silent straight through 3" exhaust you've ever heard. Concealer404 says it's quieter than a stock MSM. Will work on posting a drive by at some point.

I am glad it is quiet enough for you. I don't think I could fit another resonator under the car. Now go smoke those muscle cars that can't hear you coming.

Adding 2 resonators is not something I am going to regularly do, they don't fit in my standard boxes.

Haha, good point! They won't even know I'm there till they hear the blow off valve :-P

Yeah I am not completely happy with the noise of the BOV, but it beats out throwing in a $250 TIAL BOV on a budget setup.

It appears to work as it should, but it sure does like to talk a lot.

You should name it "Chatty Cathy" in your kit.

Add a muffler of sorts to the BOV. Plumb it to an expansion tank lined with sound deadening material and a filter on it where the air comes out of the tank.

It's not really that annoying and i don't think it hits the frequencies that give Nick pain.

It's just more noticeable because of how ridiculously silent the car is.

Yeah, the BOV noise doesn't bother me, I think it sounds cool :-)

you could just recirculate it.

Shuiend, post pics pls? :x:

Attachment 229942

I think that is the only one I took.

I had a good one that i sent to @vteckiller2000 but i've deleted it since. Maybe he can easily come up with it? It was REALLY nice. Much impress.