As the title says, Has anyone ever welded a muffler in an aftermarket downpipe?

If so, what brand and size muffler?

There seems to be enough room to fit a very small muffler - perhaps something custom from a race muffler shop like Coast Fab, Burns, Vibrant. Those are usually able to stand up to high heat and are often re-packable.

I'm contemplating doing this to quiet the car down a bit. I know Speed of Light did it on his car but he custom fabbed his own muffler entirely. It made a nice difference. I don't have those skillz so I'm trying to see if anyone else has done this and sourced a muffler.

Yes, I'm getting old but I love the FD.

 

I thought about doing this on my last FD. Was going to put a Burns muffler but went with a high flow cat in the midpipe to cure my boost spike issue. I seen it before though and actually entertaining that idea again for my next one.

 

I would think that heat might be an issue? You'd definitely have to have the right type of muffler to make it work without burning to a crisp within a few hundred miles.

 

I think about this sometimes..

However, I think a real solution is to move the catalytic converter closer to the engine and then put the biggest oval mufler that fits where the standard catalytic converter goes, and then use the biggest rear muffler that fits.

Take a look at the following parts

FD silent sport catalyzer ADT R Magic GARAGE / FD
80φ sport catalyzer of pure exchange type is (with silencer). ||| Revolution :: Catalogue
METALLIC SUBSTRATE CONVERTER WITH MUFFLER - MAZDA RX-7 (its about the middle of the page) SMB Full Exhaust Systems-Mazda RX-7

I am thinking about using one of these or getting a custom one made. I wasn't sure how well the system would hug the underbody and also if there might be heating problems putting the catalytic converter away from the OEM head shields.

 

doesnt a resonator work thesame way ? lowering the volume? I used a huge resonator on the car and I think it quieted it down quite a bit .

 

That SMB cat is actually pretty loud; I have Alberto's old one.

With a 3" downpipe and 3" Magnaflow Ti cat back it was loud, not as loud as with just a burnt out presilencer, but loud.

With the Ebay OBX-R large oval muffler 3 1/2" cat back it is pretty quiet, but stock main cat is still way more quiet.

I think a metal core precat at the end of the downpipe in addition to the stock main cat would really be whisper quiet and still take less heat abuse than the stock close coupled precat does.

 

What do you have in the space where the main cat goes?

 

If noise is the concern, why not use a thicker material for the downpipe or have a double walled one built, then put a muffler where the stock catalyst goes? Does that much noise really come through the metal?

 

A really good heat wrap will take out the high pitched tings. I used DEI Titanium wrap on my mustang's ss catless x-pipe and it made a huge difference.
just my 2 cents

 

Blue, Jobro

FYI, From purely a subjective perspective, that SMB sounds only a little louder than the Bonez from what I could tell at the time I switched out. However, the tone of the SMB is much better than the Bonez high flow cat since the muffler in the SMB rids the system of some of the high pitched rotary exhaust tone.

I could of course just install the stock cat but I don't want to burn up an expensive stock cat. I need it for smog. The stock cat is awesome for sound control, tone and emissions. I suspect I could probably pass smog with the Bonez, tuning, oil with minimal amounts of ZDDP and stock plugs but it's easier to just throw the stock cat back on.


Some history...

I once tried a Random Technologies metal core cat in the midpipe by itself - no other muffler in there. Didn't make much of a change in sound. Didn't notice much of a difference in power output either according to the butt dyno. It did help with boost control through - especially in cold weather. I have a thread on here somewhere from 7-8 years ago.

BTDT

The heat wrap does indeed help to quiet the noise coming from the front of the car but it is a very small amount. I'm looking for a bigger amount of quieting.


The stock downpipe has a big pre-cat that acts as a muffler. When you add an aftermarket downpipe w/o a pre-cat (or muffler), you get more exhaust noise at the front of the car and therefore inside the cabin. It's kinda like adding a header to a normally aspirated car.


double wall would definitely help but I don't have the skillz to do that myself and welding in a muffler should be more cost effective than paying someone for GOOD fab work.

^If there are any custom fab guys reading this, I'd like your opinion on that^



My goals / What I want is to:
1. quiet the overall exhaust sound levels
2. quiet the level of sound at the front of the car - which has an impact on how much sound you hear when you are sitting in the car driving.
3. better tone (of course this is subjective)


Muffler is an easy way to accomplish these 3 goals. I'm going to be removing the downpipe to fix an exhaust leak over the winter so this would be a convenient time for me to do this.

 

I have a black halo resonator about 12" past my wastegate. I would consider it to be in the area traditionally referred to as a downpipe. My car is quiet for a 3" single turbo car, except at idle. Still loud at idle.

 

Why would you want to put a muffler in the downpipe, just put a big muffler in the back and call it a day. I built a muffler for a 3 rotor turbo car, 3.5" exhaust all the way back with a single muffler in the back. The muffler measured 7x18" and packed it with stainless steel wool and a high temp fiberglass packing.

 

the obxr catback necks down to like 2 inch at the tip.... unless i'm thinking of the wrong thing. that is why its quieter than most but also very restrictive

 

the obxr catback necks down to like 2 inch at the tip.... unless i'm thinking of the wrong thing. that is why its quieter than most but also very restrictive

Yes, my OBX-R catback was that way.

I reached up the exhaust tip and cut the ~2" stinger out of the exhaust exit of the OBX-R cat back with a die grinder/cut off wheel and the it is still very quiet compared to my previous 2.5" straight pipe or my 3" canister style Magnaflow Ti and because of the 3.5" diameter it has a deeper tone.

It is a large, heavy, stainless steel packed muffler- so it works well.

 

Have you considered cutting open the stock pre-cat, knocking out the ceramic matrix, stuffing the now empty cavity with some sort of stainless steel packing or other material, then re-welding it back together?

 

I just bought a Revolution 80mm silent mid pipe with a catalytic converter.

I've tested out the following configurations now.

Setup #1:
Standard N3G1 99-02 FD JDM dump pipe (no precat in those) + Standard cat pipe + standard N3G1 99-02 catback (there is a difference!)

Notes: Quiet, more engine noise than exhaust noise. Tiring to drive fast with engine noise.

Setup #2:
Standard N3G1 99-02 FD JDM dump pipe (no precat in those) + Standard cat pipe + Gandor Vertex Titan GD730 Titanium Cat back.

Notes: Lots of reverberation from diameter changes in exhaust. Noisey.

Setup #3:
Standard N3G1 99-02 FD JDM dump pipe (no precat in those) + 80mm Knight Sports Metalit Pro-200 Cat converter (120mm 200cell cat converter) + 80mm Gandor Vertex Titan GD730 Titanium Cat back.

Notes: Less reverberation due to less diatmer changes, louder than standard with just the catback. Better exhaust noise, just louder.

Setup #3
Re-Amemiya JDM 80mm front pipe (these have the hammered flat section to clear RHD steering shaft) + 80mm Knight Sports Metalit Pro-200 Cat converter (120mm 200cell cat converter) + 80mm Gandor Vertex Titan GD730 Titanium Cat back.

Notes: Much less reverberation at any speeds because there are now no step changes. Quite loud when racing but quiet with sequential twins, quiet at idle. Becomes tiring when driving at high rpm for extended periods of time.

Setup #4
Re-Amemiya JDM 80mm front pipe (these have the hammered flat section to clear RHD steering shaft) + 80mm Revolution Silent Mid pipe (100mm 150cell cat converter + oval muffler) + 80mm Gandor Vertex Titan GD730 Titanium Cat back.

Notes: Not yet tested!

 

Finally got to test Setup #4


Setup #4
Re-Amemiya JDM 80mm front pipe (these have the hammered flat section to clear RHD steering shaft) + 80mm Revolution Silent Mid pipe (100mm 150cell cat converter + oval muffler) + 80mm Gandor Vertex Titan GD730 Titanium Cat back.

Notes: Very quiet. Idle is quiet, fast idle is quiet with the A/C on. Quiet Cruising at 2000-2500. Quiet accelerating. The noise gets slightly higher at full highway cruising speeds but its absolutely great around town. If I do anything now I will look for a quieter titanium catback, basically just one with a bigger muffler (the tradeoff will be slightly more weight). Some car guys would now say the car is too quiet, it has certainly lost a lot of its roar.

 

As mentioned finding one that will handle the heat is likely expensive and difficult

There's a reason the SMB DP with cat cost 1k