Turbo exhaust- effect of adding resonator

Paulus · Postby **Paulus** » Fri Jul 10, 2015 10:10 pm

Noted.

Given the CAT bolts directly to the dump pipe, I would have to replace the dump pipe to make any improvement?

My next port of call if I was to reduce drone would be going to the muffler or getting another resonator? Or even another muffler? Ie what's the cheapest solution ;)

timk · Postby **timk** » Fri Jul 10, 2015 11:19 pm

What exactly is your current rear muffler and tip?

Paulus · Postby **Paulus** » Sat Jul 11, 2015 1:18 pm

Postby **NitroDann** » Sat Jul 11, 2015 2:08 pm

Lets get some terminology straight

This is a muffler, this one happens to have a straight through design based on my experience looking at it.

This is a hotdog, a hotdog is identical to the above, except its sausage shaped and small.

This is a 'cannon'. A cannon is a hotdog with a cylindrical shape rather than a sausage shape and a big tip designed for being displayed at the rear of the car.

This is a baffled, or chambered, muffler

This is what the inside of any straight through muffler, or hotdog looks like.

Therefore the difference between a hotdog and a straight through muffler is the shape, and hence the total sound absorption material that can fit into it (stainless steel wool or fibreglass wool).

What you appear to have is a small hotdog (especially small straight through sausage shaped muffler) and a very small oval bodied muffler (small oval shaped straight through muffler).
What you need a hotdog muffler which is 18 or 22" long with a 5" round body (sausage or cylinder shape doesnt matter, sausage is usually cheaper and wont catch on speedbumps) and an oval muffler under the boot, which is a LOT larger than you have.

This is the relative size of what you have VS what people who ask me for a wife friendly exhaust get, under the boot area.

You appear to have a 12" hotdog, they come up to 30" long

Dann

Paulus · Postby **Paulus** » Sat Jul 11, 2015 2:19 pm

Thanks for the clarity- I enjoyed the euphemisms too (even if they are only in my mind).

I've gone for the smallest of all options by the sounds of things. I knew the muffler wasn't the largest as I asked for minimal restriction to make any attempt to improve turbo spool.

I think I'll cease the journey of changing exhaust parts as its cost prohibitive for the gain.

One last clarification.. Exhaust noise itself comes from the entire system or notably the muffler? I ask this as I have a thin aluminium heat shield under the boot rather than the traditional oem. I wonder in my last search for a cheap mitigation I should go buy an oem heat shield and be done with it.

It's not too bad, but the trade off in turbo usability is probably a sacrifice I need to make. Also trade off in price. The whole system has cost me $400 including welding in the external wastegate

speed · Postby **speed** » Sun Jul 12, 2015 9:01 am

Forget the cost. Trying to do something cheaply creates dramas.
Instead work out how to do it properly based on what works and be prepared to pay the money.

Otherwise you end up trying to fix a product that was designed poorly from the start.

You can polish and glitter a turd all you like. At the end of the day it is still a turd.

I suspect that a well made 3 inch system would have more power and still less drone than what you are getting now.

Sometimes I get too caught up in work and I stress out and make irrational decisions at home. It always bites me hard. Reality is that planning and research up front reduce unexpected issues or problems later on.

I think you need to bite the bullet on this one and either live with what you have, or spend more money replacing further bits or put some of your white collar earnings away and buy a proper system.

Quality costs and some are more prepared to pay it than others. ;)

IanR · Postby **IanR** » Sun Jul 12, 2015 8:25 pm

NitroDann wrote:Lets get some terminology straight

This is a muffler, this one happens to have a straight through design based on my experience looking at it.

This is a hotdog, a hotdog is identical to the above, except its sausage shaped and small.

This is a 'cannon'. A cannon is a hotdog with a cylindrical shape rather than a sausage shape and a big tip designed for being displayed at the rear of the car.

This is a baffled, or chambered, muffler

This is what the inside of any straight through muffler, or hotdog looks like.

Therefore the difference between a hotdog and a straight through muffler is the shape, and hence the total sound absorption material that can fit into it (stainless steel wool or fibreglass wool).

What you appear to have is a small hotdog (especially small straight through sausage shaped muffler) and a very small oval bodied muffler (small oval shaped straight through muffler).
What you need a hotdog muffler which is 18 or 22" long with a 5" round body (sausage or cylinder shape doesnt matter, sausage is usually cheaper and wont catch on speedbumps) and an oval muffler under the boot, which is a LOT larger than you have.

This is the relative size of what you have VS what people who ask me for a wife friendly exhaust get, under the boot area.

You appear to have a 12" hotdog, they come up to 30" long

Dann

Gotta score some points for that post!

mr bender · Postby **mr bender** » Sun Jul 12, 2015 9:07 pm

Looks like the diff is falling out. :?:

Postby **NitroDann** » Sun Jul 12, 2015 9:19 pm

Good eyes. Yes the diff hoising has a notch on that low side designed to be the weak point and avoid further damage. It does looks like a broken housing

Paulus · Postby **Paulus** » Sun Jul 12, 2015 11:04 pm

Broken housing?! You mean the notch on the control arm or something else? I'm
Not seeing anything :/

Let me know if this is a major safety concern

So just by way of an update I took a leaf out of this book today as I have an aluminium heat shield http://forum.miata.net/vb/showthread.php?t=218666 and had great success installing rubber grommets:

http://youtu.be/T2tuMIyvktc

One day I'll I hope to get rid of the chavvy air dump sound by fitting a proper airbox, recirc doesn't seem to help

hks_kansei · Postby **hks_kansei** » Mon Jul 13, 2015 1:14 pm

Paulus wrote:Broken housing?! You mean the notch on the control arm or something else? I'm
Not seeing anything :/

Let me know if this is a major safety concern

It looks like the diff is angled slightly in relation to the subframe, when it shoudl be level.

Just jack the back of the car up and have a look, the diff is held in by the front bolts on the PPF bar, and two larger ones directly onto the subframe on the moustache bar (big arms that come out of the diff, will be above the driveshafts)

It's not unheard of for one of the arms to crack or snap, so check they both look normal. (and that the bolts at the ends are still there)

Also grab the diff and try to rock it around, it shouldn't have much movement (maybe 10mm either way if you're got OEM bushes)
if you can rock it around a fair bit, it's a sign something's buggered (either bushes are dead, or somehting's snapped)

if the housing is broken, you'll really want to get a new housing soon since the whole weight off the diff will be hanging from the PPF, and in turn the gearbox.

edit:
of course, that's all worst case stuff.
It is equally likely that it just looks funny because of the angle of the photo

RS2000 · Postby **RS2000** » Mon Jul 13, 2015 1:23 pm

The cooling fins on the diff should be at 90 deg to the floor, so it's more than just the photo angle.

Cheers

Paulus · Postby **Paulus** » Mon Jul 13, 2015 9:37 pm

The diff is fine, it's just angles and perspective. All bolts are fine:

On the positive I learnt about the weak zone of the diff and how it's used as part of the crumple zone for the car. V interesting. Rx7 housing doesn't have this.

bruce · Postby **bruce** » Tue Jul 14, 2015 5:20 pm

More interesting is the tow bar set up! The cut out almost looks factory. I've never seen one like that on a 5 (I've seen a few ugly ones which hang below the bumper).