More Restrictive Exhaust Part?

So I'm wondering, which is more restricting on the exhaust: the muffler and resonators? Or the catalytic converter?

Just looking into ideas for a track exhaust on the Miata and a test pipe and stock cat-back would be easier to find and cheaper than a good cat-back system, and probably about as loud, too.

Most modern cats aren't much of a restriction, but its pretty application-dependent and I'm not a Miata expert.

Typically the stock muffler is more restrictive than the resonator - both because it does most of the muffling, and because its further up the exhaust stream. As hot exhaust gasses go back and cool, they reduce volume, so flow requirements are reduced the further back you go.

curtis73 wrote: Most modern cats aren't much of a restriction, but its pretty application-dependent and I'm not a Miata expert.

What constitutes "Modern"? I'm looking at an OBD-1, '94.

I would think pre 90s.

After much searching, I think I found a page that answers my questions. I really wanted some Dyno graphs to compare different potential builds. Guess who has a bunch of dyno graphs comparing cars with different mods? Flyin' Miata! http://www.flyinmiata.com/tech/dyno.asp

I think their comparison of a stock '96 with a stock and a turbo exhaust will be the most similar to my purposes: http://www.flyinmiata.com/tech/dyno_runs/Robert_Webb_082099.pdf 4.3tq and 4.6hp from an exhaust alone.

If I want even more power, I can slap in a test pipe for track-only insanity.

Well, maybe it doesn't, because it doesn't show how much power would be gained by replacing the cat. Exhaust just strikes me as one of those systems that only works as well as it's most restrictive component though (but I could be totally wrong).

You've pretty much got it. Start with the biggest bottleneck and work from there.

Keith wrote: You've pretty much got it. Start with the biggest bottleneck and work from there.

Judging by the results you got on your dyno graphs, it looks like that's probably the muffler, then the cat or header. Car already has a header on it though...

Not all resonators are created equally.

Some are like glasspacks, some are like baffled mufflers (not good).

curtis73 wrote: Typically the stock muffler is more restrictive than the resonator - both because it does most of the muffling, and because its further up the exhaust stream. As hot exhaust gasses go back and cool, they reduce volume, so flow requirements are reduced the further back you go.

that's all well and good.. but most cars have their mufflers at the very end of the exhaust system now

There are way too many variables to make a blanket statement of cats are more restrictive than mufflers or such.

GM pellet cats are terribly restrictive for example. Terribly restrictive. While Ford and just about everyone else used a matrix cat, which was not particularly restrictive. Until it plugs up or melts. Then it's just as restrictive as the GM pellet cat.

Toyota hides a tremendous restriction in their oem mufflers. Take one apart some time and you'll see it. That inlet pipe necks down to about 3/4" inside. Makes the vehicle nice and quiet. Toyota isn't the only one to do this, ever listen to the hiss of a Caddy or Lincoln when floored?

Probably the closest to a blanket statement you could make is that an oem resonator is not the worse restriction in a typical oem exhaust. That statement would not apply to aftermarket resonators, especially if installed backwards (happens quite a bit).

Salanis wrote: So I'm wondering, which is more restricting on the exhaust: the muffler and resonators? Or the catalytic converter? Just looking into ideas for a track exhaust on the Miata and a test pipe and stock cat-back would be easier to find and cheaper than a good cat-back system, and probably about as loud, too.

Ever hear of a magazine called Grassroots Motorsports? I understand it's pretty good one, but I seem to recall that a little while ago, they had some article about Miatas, catalytic converters, and chassis dynos.

You may want to find a library that has this magazine otherwise known as GRM- may be helpful to you.

Eric

One thing to remember about the FM Turbo exhaust. Without a turbo upstream, they're LOUD. For fun, a couple friends swapped exhausts. I've heard it. Not a good loud, either, a "Hey Officer, come pull me over" loud. Better perhaps than a Spec Miata exhaust in that it didn't sound like a swarm of angry hornets, but likely just as loud.

The new Spec Miata (SM) exhaust now has no pipe behind the rear axle. None. No muffler, no pipe. Just a dump tube pointing down at the ground. It's stupid loud.

I had a new exhaust built for my turbo Miata. It used Moroso spiral flow mufflers. Here's the construction:

downpipe from turbo - cat - moroso spiral flow muffler (SFM) - another SFM.

Here's a page on that muffler. It's the second one down. http://www.moroso.com/catalog/categorydisplay.asp?catcode=35054moroso spiral flow muffler

My application is stock quiet at idle. A bit louder at cruising speeds. A smidge or two louder at full throttle. I can cruise with the top down comfortably. It does not sound like a fart can exhaust.

alfadriver wrote: Ever hear of a magazine called Grassroots Motorsports? I understand it's pretty good one, but I seem to recall that a little while ago, they had some article about Miatas, catalytic converters, and chassis dynos. You may want to find a library that has this magazine otherwise known as GRM- may be helpful to you.

Well, how long ago? What issue was that in? I'll look through my back issues, but I don't recall anything about messing with Miatas and cats.

No idea- my stack is back home. I do know they tested 3 or 4 different ones and even compared that to a test pipe. Test pipe was not as good....

E-

I found the issue. It's May 2008. Cover article is "BIG DREAMS, small price" and has a blue WRX. Same issue as the write-up on the Sucker Vette.

Xceler8x wrote: The new Spec Miata (SM) exhaust now has no pipe behind the rear axle. None. No muffler, no pipe. Just a dump tube pointing down at the ground. It's stupid loud.

When did this change happen?

My understanding is that the Spec Miata rules changed, opening up the restrictions on exhaust components. The original Mazdacomp Bosal exhaust that used to be spec is no longer the hot item because it didn't have as much engineering put into it. But it still gets run for SSM and as a common option to make sound at Laguna.

But this is the first I heard that they completely redesigned it.

Here's a pic of a car sporting the new exhaust. This is my friend Adrian's SM car.

Xceler8x wrote: Here's a pic of a car sporting the new exhaust. This is my friend Adrian's SM car.

And that's the current one from Mazdacomp? Hrm... that's not the one I was wanting. No way that will be quiet enough for my needs.

Just spoke to them. The rep said the part has not changed since it was introduced. It still has the same design, part #, manufacturer, muffler location, and everything that it always did. I asked about tail pipe location, and he confirmed that it exits in the same stock location.

Xceler8x wrote: Here's a pic of a car sporting the new exhaust. This is my friend Adrian's SM car.

I know this is off topic for what Salalnis is looking for, but was there a reason they didn't do a simple exit in front of the rear tire?? Save some plumbing, and be sure that the exhaust has no path to the driver....

E-

alfadriver wrote:

Xceler8x wrote: Here's a pic of a car sporting the new exhaust. This is my friend Adrian's SM car.

I know this is off topic for what Salalnis is looking for, but was there a reason they didn't do a simple exit in front of the rear tire?? Save some plumbing, and be sure that the exhaust has no path to the driver.... E-

The frame rails are looooow. Our $08 car cant get out of my driveway with a ovaled 2" side exit exhaust.

It may be in the rules. Plus, dumping exhaust in front of a rear tire often means one hot rear tire - a coworker has that problem with his Locost.

Salanis wrote: Just spoke to them. The rep said the part has not changed since it was introduced. It still has the same design, part #, manufacturer, muffler location, and everything that it always did. I asked about tail pipe location, and he confirmed that it exits in the same stock location.

This exhaust wasn't from Mazdacomp to my knowledge. Adrian is pretty anal about keeping the car to SM spec so I'm sure he did his homework on legality of the exhaust for SM.

I can ask him where he got it from if you'd like. But you're right..it is crazy loud.

Xceler8x wrote: This exhaust wasn't from Mazdacomp to my knowledge. Adrian is pretty anal about keeping the car to SM spec so I'm sure he did his homework on legality of the exhaust for SM. I can ask him where he got it from if you'd like. But you're right..it is crazy loud.

Makes sense then. As I understand, the exhaust rules aren't too strict for SM. You pretty much just need to make sound for whatever track you're at.

The Mazdacomp exhaust is supposed to be one of the quieter ones.