Exhaust size vs power vs noise

In reply to drock25too :

Super trapps  do reduce sound at a cost to power. The turbulence at the end of a pipe works against the dispersion of sound 360 degrees. 

I made as much power as you with a single 1 7/8 exhaust tip, in an exhaust sensitive rotary.

The further from the engine, the more the exhaust contracts.  You can go smaller, some people feel you SHOULD go smaller.

Pete. (l33t FS) said:

I made as much power as you with a single 1 7/8 exhaust tip, in an exhaust sensitive rotary.

The further from the engine, the more the exhaust contracts.  You can go smaller, some people feel you SHOULD go smaller.

Maybe he could shrink the outlet from the glasspack down to a single 2" and use a turndown at the end to aim the blat blat at the ground?

I still think cats would be worth adding as well.

I believe turn ups vw turn downs would likely read quieter...

I had thought about cats. Honestly. Then talked myself out of them due to space constrains. as well as not knowing how bad for them it would be die to location. etc.

However,  thinking through everything said here, as well as looking at what gm used for exhaust on these engines,  it seems like i am at extreme overkill in size currently. 

Gm used 2.25 exhaust from the factory on the 3.5, which is the biggest hp engine this car is likely to get. 

Thats with super restricted (ASSUME) muffler, crush bent tubes, etc.

So in my mind,  after all tjis, it sounds like i could toss the already owned oval miffler and tip inder the back (2.25 inclet), and it wouldn't really hurt me at all. Maybe a couple horsepower,  but not huge.

If i want to go nuclear,  2.25 or 2 inch drom the 2.5 collectors on the headers to a y pipe and 2.5 exhaust with an oval muffler, cats. A resonator,  and a turndown at the bumper.

Right?

And again,  the primaries are 1.5, NOT 2.5

I ran a large SuperTrapp muffler, one with the fiberglass stuffing and the plates at the back end, as the sole quieting on my mid-engine Mini with its dead-stock Honda H22A1.

At Laguna I got black-flagged for noise, so pulled in to remove some plates. It was that day that cemented my disgust with the muffler in general. First, they used stainless housings, nuts, and bolts. Even though I was using high-temperature anti-seize, several bolts holding the plates on seized up and sheared off. Fine, "eff it", and ran with what was left, having removed about half the plates. Guess what... I get black-flagged again for noise, pull in, and discover that it was now producing so much back pressure that the stuffing was getting pushed out, AND two more of the bolts sheared off. As I wrote at the time, they somehow hit on the rare combination of being both very loud AND restrictive. I won't use them again.

In reply to rslifkin :

yes, too big,  should be 1.375/1.5 with a 2.1/8 exhaust pipe.

... who writes a fraction like "2.1/8"?  Also who is buying 2.125" exhaust pipe?  Either 2" or 2.25".

I would use a packed muffler long before installing a converter if the goal is motorsports.  Wouldn't want the fire risk.

Key to killing drone is getting mufflers as far forward in the exhaust system as possible.  If you can slam the largest perforated core packed mufflers you can right on the collector, even better.  Internal volume is important.  More internal volume = more noise reduction.  Those cutesy little bullet mufflers do nothing but make your wallet lighter.

Look at what quiet rotary exhausts are if you want an idea of what works.  Basically a chain of large external diameter perf-core mufflers with little bits of pipe to connect them, and a biiiiig one at the back.

I keep stressing perf core.  Louvered core mufflers are cheap and they are also heinously restrictive.

pres589 (djronnebaum) said:

... who writes a fraction like "2.1/8"?  Also who is buying 2.125" exhaust pipe?  Either 2" or 2.25".

With standard 16 gauge tubing, 2 1/2 OD tube is 2 3/8" ID, 2 3/8" OD tube does not exist except as 2 1/4" ID slip joints.

I thought the way to kill drone was to get a muffler as close to the outlet as possible keeping the last length of pipe short.  I base this on a bunch of listening to exhaust samples for Fox/SN95 Mustangs and then other vehicles with similar setups but shorter "end of chain" pipes.

pres589 (djronnebaum) said:

I thought the way to kill drone was to get a muffler as close to the outlet as possible keeping the last length of pipe short.  I base this on a bunch of listening to exhaust samples for Fox/SN95 Mustangs and then other vehicles with similar setups but shorter "end of chain" pipes.

Drone is annoying to the driver, but probably not what's spiking the sound meter.

You have a 200 rwhp non-turbo Miata, which is roughly what an M62 supercharged 1.8 makes.  I'm pretty sure there's an off-the-shelf solution for this -- don't know what it is off the top of my head, but I'd probably call up the guys at Goodwin Racing and ask them what they'd recommend for passing sound at Laguna.  You could ask the guys at Flyin' Miata too, but they tend to have more turbo-oriented solutions, and the turbine reduces noise by a ton all on its own.

In reply to codrus (Forum Supporter) :

Driver fatigue is important, too.  And a droning exhaust will beat you up long before you realize you feel like your head has been hammered flat.

codrus (Forum Supporter) said:

pres589 (djronnebaum) said:

I thought the way to kill drone was to get a muffler as close to the outlet as possible keeping the last length of pipe short.  I base this on a bunch of listening to exhaust samples for Fox/SN95 Mustangs and then other vehicles with similar setups but shorter "end of chain" pipes.

Drone is annoying to the driver, but probably not what's spiking the sound meter.

You have a 200 rwhp non-turbo Miata, which is roughly what an M62 supercharged 1.8 makes.  I'm pretty sure there's an off-the-shelf solution for this -- don't know what it is off the top of my head, but I'd probably call up the guys at Goodwin Racing and ask them what they'd recommend for passing sound at Laguna.  You could ask the guys at Flyin' Miata too, but they tend to have more turbo-oriented solutions, and the turbine reduces noise by a ton all on its own.

 

Turbo's do two things. Muffle the sound ( you have a rotating baffle doing that). Plus because all of the exhaust pressure is in front of the turbo and you have the air being pumped into the cylinder instead a vacuum creating a place for air to go the exhaust system no longer functions as a back door way to help creating that vacuum.  Since that's the case, it doesn't matter how big the exhaust pipe is. The bigger the pipe the lower the tone is. 
 

As a side issue. When mufflers are near or at the end of the exhaust. They are resonators.
    The Jaguar XKE has a pair of mufflers followed by resonators. Remove the mufflers and without the resonators the drone at freeway speeds quickly leads to insanity.  But just remove the mufflers and leave the resonators and while it is louder it's a pleasant loudness.  

frenchyd said:

In reply to kb58 :

Wave theory, it actually works. 
Here's the background.  Listen to a Tuba. Then listen to a clarinet. The big air volume required to play a Tuba loud compared to the Clarinet should give you an idea of why this works. 
     Now we have to go to the camshaft. When the valve starts to open air flow is relatively small compared to when the valve is wide open. So the exhaust "note" comes in the form of a wave.  
     Headers, properly designed headers ( not simply tubular exhaust manifolds)  will pulse that wave out. To make peak power the full wave needs to hit the collector at full wave and be "pushed" out by the following wave.  That's why length and diameter are so critical. That's the horsepower part of this equation. Trust me the maths are complicated but luckily there are plenty of sites that will do the maths for you. But you do need to know things like flow rate and camshaft specs. No strip street is not a spec.  Lift and duration are.  
Stepped exhaust is what is next for muffling. 
 Primary pipes lead to collector, collector leads to exhaust pipe. Leads to muffler, leads to tail pipe, leads to outlet. 
    Each needs to increase in diameter and is most effective if the connection is after a complete wave pulse.  
The computer gave you a length for primary pipes and a diameter.  The collector is larger but shorter.  Using that volume let's say it's 22.8 fluid ounces. That is the magic number. The exhaust pipe needs to be 22.8  fluid ounces. But because it's the next larger sized pipe it will be shorter, the muffler?  You can only use the tube size and guess at how much larger the effective absorption materials are. Let's say 22" ? Plus 10%?   Then there is the practical matter of what is available.
Followed by tail pipe of the next diameter again 22.8 fluid ounces. And outlet normally a turn down again the next size or two larger. 
What?  It doesn't come out to your rear bumper or the side of your car?   Good, there is no rule that it has to.  Sound bouncing off the pavement scatters. The under chassis turbulence adds to that scattering. The more turbulence the  quieter it will go past the sound meter. 

Good info, and very well written.

Just for kicks, The FiST exhaust is 55mm or for you hold backs, 2.17".  that's almost 2 3/16".

 That's probably where some of the odd inch sizes came from, converted from metric.

I'll close the door on the way out,

Happy New Year to all

Complete post header system on my GM 3.4. The Magnaflow alone leaves an annoying rap but the Pacesetter resonator added after it removes that.  All in 2.5" tubing.

Not to hijack the thread too much but...

I'm starting to design the exhaust for the Yamaha powered FMod.  Now, I can't get a lot of length, maybe 35 to 40 inches after I turn and point backwards.  Would I gain much (quieting-wise) if I turn the outlet(s) downward INTO the diffuser tunnels?