mufflers

jeremy gast · **Posted:** Tue Nov 29, 2011 3:23 pm

So I am designing the new exhaust for the miata. Right now I am running a cat and then one muffler. I want to ditch the cat and run two mufflers and a turn down. Right now i am looking at two dynomax mufflers.
http://www.jegs.com/i/Dynomax/289/24215/10002/-1
In my searching, some one said that if you ran the same muffler back to back you wouldnt really be doing anything with the second muffler cause the flow is exactly the same. I have never heard such before but wanted to get everyones opinion??

Vincent Keene · **Posted:** Tue Nov 29, 2011 3:38 pm

jeremy gast wrote:

In my searching, some one said that if you ran the same muffler back to back you wouldnt really be doing anything with the second muffler cause the flow is exactly the same. I have never heard such before but wanted to get everyones opinion??

I can verify that two glass-paks = one glass-pak as far as sound level. We added a 2nd one to our Prelude and it's as loud as ever.

SimonWright · **Posted:** Tue Nov 29, 2011 7:23 pm

Does it need to be inspectable? Just had my rally car inspected at a racer friendly station and even they wanted to know where my cat was.

Simon

RichardNuss · **Posted:** Tue Nov 29, 2011 9:09 pm

SimonWright wrote:

Does it need to be inspectable? Just had my rally car inspected at a racer friendly station and even they wanted to know where my cat was.

Simon

In that case, why not leave the cat shell in place with the guts removed from it?

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

Vincent Keene wrote:

jeremy gast wrote:

In my searching, some one said that if you ran the same muffler back to back you wouldnt really be doing anything with the second muffler cause the flow is exactly the same. I have never heard such before but wanted to get everyones opinion??

I can verify that two glass-paks = one glass-pak as far as sound level. We added a 2nd one to our Prelude and it's as loud as ever.

We have 2 cherry bombs plus about 3' of tubing after, with two 90 degree bends and a turndown tip under the car. Sounds fantastic, not too loud at all. Streetable, barely.

We tested with just one (in the garage) and said "too loud, add another". Seemed to do the trick for us. Maybe it's the extra bend and turndown we have that makes it quiet?

Scott Lusted · **Joined:** Tue Oct 27, 2009 9:52 am **Posts:** 215

Years ago, I did a dyno session with the old Miata and worked on intake, timing, and exhaust.
This was on a 91.

Tested stock system, the spec miata exhaust from Mazdaspeed, open pipe that turned down just past the rear diff, and then added a dynomax super turbo (quiet street muffler but sized correctly).

The open was 1-2 hp above the others, but less torque. LOUD even with ear plugs...
Mazda unit made good power but would be too loud for the street.
Dynomax super turbo made the same power as the Mazda unit and was almost too quiet.
All ran 2.25" tubing.

Stock unit was -9 on average..

YMMV....

-Scott

Vincent Keene · **Posted:** Wed Nov 30, 2011 9:14 am

MikeWhitney wrote:

We have 2 cherry bombs plus about 3' of tubing after, with two 90 degree bends and a turndown tip under the car. Sounds fantastic, not too loud at all. Streetable, barely.

We tested with just one (in the garage) and said "too loud, add another". Seemed to do the trick for us. Maybe it's the extra bend and turndown we have that makes it quiet?

Stephen told me that was your setup so we're baffled as to why ours is so much louder than yours. In addition to the 2 glass-paks we have a Car Chemistry insert in there too! FYI, we have only one 90 bend and a 60 degree turn-down.

Jason Tower · **Joined:** Wed Jun 11, 2008 3:31 pm **Posts:** 1173

Vincent Keene wrote:

MikeWhitney wrote:

We have 2 cherry bombs plus about 3' of tubing after, with two 90 degree bends and a turndown tip under the car. Sounds fantastic, not too loud at all. Streetable, barely.

We tested with just one (in the garage) and said "too loud, add another". Seemed to do the trick for us. Maybe it's the extra bend and turndown we have that makes it quiet?

Stephen told me that was your setup so we're baffled as to why ours is so much louder than yours.

probably because, all other things being equal, noise is proportional to horsepower

jeremy gast · **Posted:** Wed Nov 30, 2011 11:16 am

I dont care about inspection I can get around that! I need to meet sound regulations of under 100db and would love to be under 90 db. hmmmmmm

Makes me wonder about one muffler and then one glass pack.

MikeWhitney · **Joined:** Wed Aug 20, 2003 9:15 pm **Posts:** 4724

You guys using the cute little cherry bombs or the big manly ones?

http://www.jegs.com/i/Cherry+Bomb/545/87520/10002/-1

http://www.jegs.com/i/Cherry+Bomb/545/87516/10002/-1

Vincent Keene · **Posted:** Wed Nov 30, 2011 11:20 am

MikeWhitney wrote:

You guys using the cute little cherry bombs or the big manly ones?

The longer ones IIRC. We got them from Summit.

Cash Davidson · **Posted:** Wed Nov 30, 2011 2:42 pm

I'm working on the same thing for my V6 Mazda. I was thinking about coming from the headers into a single 2.5", then a muffler and a turn down. Maybe I should do an H-pipe, two mufflers and two turn-downs. Wadaya think? I have two of the "big manly" cherry bombs in the shed that were on the Firebird at one time - obviously, I never throw anything away.

DickRasmussen · **Posted:** Wed Nov 30, 2011 3:02 pm

For you guys where the glasspacks aren't quiet enough, even with two in series:

How old are they? Any "packing" type muffler gets louder as the packing goes away.

SuperTrapps, Coastfab, Burnsstainless, etc mufflers can be repacked.

Summit sells SuperTrapps and the packing in various lengths and diameters.

Dick

jeremy gast · **Posted:** Wed Nov 30, 2011 3:11 pm

i have read that super trapps rob power and burns and coast are nice but big big money

DickRasmussen · **Posted:** Wed Nov 30, 2011 3:37 pm

jeremy gast wrote:

i have read that super trapps rob power and burns and coast are nice but big big money

Andy Hollis did a comparison in Grassroots in the last year or two.

When I dyno'd my FF engine the HP difference between an open (no baffles) 10 inch Supertrapp and the same muffler with a dozen baffles was about 1 percent at high revs.

For "subjective sound level" info, I've run the 10 inch Supertrapp at the June and October Danville autocrosses this year. No baffles. Of course my engine is low compression, tame stock cam, and no Vtech, etc. so it is relatively quiet without any muffler.

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