Help me quiet down my Miata

Pete. (l33t FS) said:

Part of the reason Racing Beat used to make their rotary exhausts out of .125" thickness pipe was for the sound effects.

The newer exhausts made of 16 gauge stainless are much more tinny sounding.  More sound is traveling through the pipe walls.

Interesting.  I've had 3 Racing Beat cat-backs on 3 different Miatas, and it's always been my favorite.  All 3 sound somewhat different, though, and I've never understood exactly why--this might be it.  The most recent one I purchased (in 2006) is louder than the other that I still have...

Keith Tanner said:

 I don't get to follow many cars that are clearly catless around here, although I was following a first gen Mustang the other day that was in serious, serious need of a carburetor adjustment. Either that or it had a leak in the fuel tank.

Hah!  If it had a cat, you wouldn't have noticed how rich it was.  But probably because it'd be clogged and stuck in the driveway:)

I'm personally glad I don't have to deal with getting the fleet emissions tested as well.  But I'd gladly do it if it put an end to the endless slew of brodozers rolling coal up the mountain pass.

An area free of emissions testing is like a non-smoking section of a restaurant, or a no-peeing area of the swimming pool.

Cats don't stop brodozers from rolling coal, alas.

There have been at least two very distinct versions of the Racing Beat header. I don't know if they've changed the internals of their mufflers, but price pressure from absolute crap exhaust systems sold on ebay could definitely be a factor. 

In reply to Keith Tanner :

Speaking of their rotary units (what I am familiar with...) the headers are still made of .125" wall pipe, or 3mm if one is so inclined.  The rest of the exhaust systems used to be the same wall thickness, and the mufflers were also made of .125 wall casings with 3/16" endcaps.  RB exhausts were seriously heavy!

About five or six years ago, maybe more, they either changed suppliers or stopped making them in house.  The mufflers are no longer packed perf-core but are chamber mufflers, made with 16ga stainless for the pipes and shells.

Unfortunately, I found that the stainless mufflers do not tolerate rotary exhaust heat and the shells will crack near the pipes, because the pipes inside the mufflers expand a lot faster than the exposed-to-air shells do.  They are also significantly louder exhaust wise than the old mufflers.  This is probably a concession to flow - I found to my surprise that the chamber muffler made no difference to power on a very backpressure sensitive engine.  But the noise was unbearable, I ended up repairing the 20+ year old muffler that I had tried to replace.  Much quieter.

The changeover happened a little after Jim Mederer died.

My R53 Mini came with a straight pipe except for one cat in the manifold and was unbearable. I ordered the longest straight through resonator I could easily fit (18") and a cheap basic thrush turbo muffler and it is very enjoyable now. Definitely louder than stock but no drone and not annoying. My Miata has no cat and a generic turbo muffler, all 2.5" and is not loud at all (the turbo helps some). 

In reply to EvanB :

Another name for a turbo is "rotary muffler" :)

It's funny, I went from driving XS-B and XS-A to ES, and I'm like, I just want one more taste of getting close to top raw or actually setting top raw. The withdrawal is real. My car needs to be a great deal better for top PAX, but I'm working on it.

I use a turbo to muffle my XS-B miata engine and beat up on Porsches. I highly recommend it for both things. I would say the biggest drawback to driving that car on the street isn't NVH, it's the 900/600 pound spring rates, but honestly it's not THAT bad.

Supercharged cars are always, well, shouty. Can always tell when one is coming down the course.

Ive fitted 5x11x22 Magnaflow mufflers in the back of these before.  So that and I would run an Ultra Quiet "resonator" from Vibrant where the cat was and a smaller bottle style unit under the tank.

If all implemented correctly power wont suffer...but it does add weight.

Exhausts choices are a pick 2 out of 3:

Weight, HP capacity(flow), volume.

Quiet with flow is heavy. Light and quiet is restrictive.  Flow and light is loud.  Etc etc.  Then cost skews those results.

dr_strangeland said:

It's funny, I went from driving XS-B and XS-A to ES, and I'm like, I just want one more taste of getting close to top raw or actually setting top raw. The withdrawal is real. My car needs to be a great deal better for top PAX, but I'm working on it.

dr_strangeland said:

It's funny, I went from driving XS-B and XS-A to ES, and I'm like, I just want one more taste of getting close to top raw or actually setting top raw. The withdrawal is real. My car needs to be a great deal better for top PAX, but I'm working on it.

I set FTD once with my Miata near the end of the '22 season and wanted to do it again the next season. Then the one guy brought his CRG Road Rebel shifter kart out of retirement and, well, that thing was guaranteed FTD unless it was raining, and my car wasn't so hot in the rain either. 

NickD said:

dr_strangeland said:

It's funny, I went from driving XS-B and XS-A to ES, and I'm like, I just want one more taste of getting close to top raw or actually setting top raw. The withdrawal is real. My car needs to be a great deal better for top PAX, but I'm working on it.

I set FTD once with my Miata near the end of the '22 season and wanted to do it again the next season. Then the one guy brought his CRG Road Rebel shifter kart out of retirement and, well, that thing was guaranteed FTD unless it was raining, and my car wasn't so hot in the rain either. 

I set FTD with my turbo Miata once.  I was in the last rungroup, it had been raining all day, stopped and dried out in the group before us, and I managed to get the A6s swapped onto the car in time when most other people either hadn't brought the Hoosiers or didn't try to swap. :)

Some random thoughts here, in no particular order:

Apparently the Good-Win cat back system has a straight-through muffler. In my limited experience, those aren't always good at killing noise under part throttle or cruise, especially not without a cat and/or a resonator. You can add one or both of those, or replace the muffler. My favorite is the seldom seen Hooker Aero Chamber. It's boat-anchor heavy and no beauty queen, but does a really nice job of killing drone and harsh notes. 21501 is 2-1/4" in and out and would probably be a good fit in place of your current silencer.

Header choice may be a factor. Isn't the Racing Beat piece a 4-into-1 design? Those tend to sound harsher than a 4-2-1 type. Conventional wisdom says a 4-2-1 is also usually better at creating area under the curve, though that is maybe a separate discussion.

You might be able to do something about the supercharger racket under the hood. Induction noises can be intoxicating or annoying. I'm assuming you have an open element cone type air filter on there now. Can you replace that with a reasonably free-flowing OEM airbox, maybe something from another car with a big engine, and duct it to pull in cool air from somewhere far away from you, like in front of the radiator?

DarkMonohue said:

Some random thoughts here, in no particular order:

Apparently the Good-Win cat back system has a straight-through muffler. In my limited experience, those aren't always good at killing noise under part throttle or cruise, especially not without a cat and/or a resonator. You can add one or both of those, or replace the muffler. My favorite is the seldom seen Hooker Aero Chamber. It's boat-anchor heavy and no beauty queen, but does a really nice job of killing drone and harsh notes. 21501 is 2-1/4" in and out and would probably be a good fit in place of your current silencer.

Header choice may be a factor. Isn't the Racing Beat piece a 4-into-1 design? Those tend to sound harsher than a 4-2-1 type. Conventional wisdom says a 4-2-1 is also usually better at creating area under the curve, though that is maybe a separate discussion.

You might be able to do something about the supercharger racket under the hood. Induction noises can be intoxicating or annoying. I'm assuming you have an open element cone type air filter on there now. Can you replace that with a reasonably free-flowing OEM airbox, maybe something from another car with a big engine, and duct it to pull in cool air from somewhere far away from you, like in front of the radiator?

The Racing Beat header is 4-1. But, I know that the Racing Beat header actually fits with the Rotrex blower, which is mounted in the hot side and hangs back towards the firewall, with the inlet tube coming off of it. Some of the other headers have the #1 and #2 primaries swoop upwards, which would cause an interference issue. The induction noise isn't bad, it's just not as cool sounding as the Eaton-style blowers, with that cool slide whistle whoop when you get on the throttle. That muffler is interesting though, I'll have to look into it.

Engine Masters tested a bunch of mufflers. They do a great job of really testing things using back to back dyno pulls, but keeping things really consistent. You can get a bunch of these mufflers at Summit, I'm pretty sure.