DIY: (Sorta) Noise reduction for HF cat
 

Those of you who've got catback exhausts and have added the CanZoomer CZMidP-4 high flow catalytic convertor with resonator KNOW that it makes a huge difference in how loud the exhaust is. In my case, I put the HF cat on and had to take it back off... it was just too loud and sounded immature. When other people with the same setup started PMing me, I decided to try to do something about it.

I first contacted David Borla (I have a Borla exhaust) who was more than willing to work up a solution. Problem was, I couldn't find anyone in California with the MidP-4 unit.

In discussing this back and forth with Shebam, we decided that a secondary muffler between the existing resonator and the Borla "can" might just do the trick. The only thing was, we wanted the 3" inside diameter perforated core muffler otherwise you're adding restriction to the 3" Borla pipe. If you do that, you might as well put the standard cat or muffler back on.

Additionally, I wanted to be sure the muffler would handle the heat of the rotary's exhaust, so I didn't even look at cheapo "glasspack" style mufflers - I went straight to the only company I could find that makes high temp glasspacks: Random Technologies. FYI, I've since found out that virtually any glasspack would work as they're far enough back that the exhaust temps are not unreasonable.

Below is a pic of the muffler Shebam and I have both since installed. The part is from Random Technologies, # 685521. It's a 12" round 3" - 3" ID 4" OD muffler. Cost is $75 before shipping.

Shebam and I both agree it reduces the noise of the HF cat + Borla by almost 50% - it's still louder than just the Borla, but not obnoxious any more. However, it *could* be made quieter... any "glasspack" style muffler of 12 - 18 inches (maximum 4" OD) can be made to fit in this location by a good muffler mechanic. Longer will obviously get you more noise reduction. If I had to do it again, I would probably get an 18" unit.

Interesting. Unfortunately not much use to those with Racing Beat exhausts. When we install murix's exhaust I'll try to eyeball the area for possibilities.
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INTERRACIAL PORN

I'm sure there's a place it'll fit, given the motivation. ;)

wait...so Omicron...straighten something out here for me...did you purchase _just_ the HT/HF cat and a straight mid-pipe or did you get the MidP-4 with the resonator and HT/HF Cat..?? Cause i want to get the newer release of CZMidP-4 coupled with the RB Exhaust but I also have to consider streetablility as well...i don't need to sound like my old Integra..."i'm a grown a$$ man!":)

XeRo,

I got the one with the resonator and it's too loud w/ aftermarket exaust. I believe Omicron got the resonator as well, but I'll let him confirm for himself.

I've ordered the part described in this thread to tone it down--btw it's on back-order.

Ben

Yes, I got the CZ-MidP4 unit which comes with the cat and the resonator. And as Ben says, it was too loud with an aftermarket catback exhaust. But with this tertiary resonator, it's back to reasonable levels.

What about the SR mid pipe/high flow CAT + a Racing Beat exhaust?? I read in the SR CAT thread, https://www.rx8club.com/series-i-aftermarket-performance-modifications-23/sr-motorsports-high-flow-cat-32945/ that RX8FOREAL claims it is pretty quiet. Any thoughts that the CZ mid pipe is louder due to wall thickness? I wonder if that has something to do with it. Just thinking while I type.

Well, the Racing Beat exhaust is supposedly pretty quiet too, so that could do it. Also looking at pics of the SR high flow cat, it doesn't look like it would flow as well as the CanZoomer/Random Technologies unit - it looks almost like the stock cat. Of course, the internal design is the most important thing, but...

What was your grand total w/labor for all this Omicron ?

Omicron,

I just got back from the muffler shop and I am very happy with the results. Thanks again for all the info!!! The car is driveable without all the stares. :)

Cost:

Resonator $75
Install: $20 - $30

Not a bad price to pay to get rid of the excess noise and less weight than the dynomat option.

just read this thread...can anyone answer my question?

i have the B&B mid pipe with no cat, just a resonator along with the Greddy SP2 cat back exhaust system. will the same technique of inserting a reversed glaspack somewhere in the exhaust help get rid of that weed wacker/pissed off bumble bee sound around 2500 6000 rpm???

any help would be greatly appreciated. i plan on going to the track on friday and i'd rather not everyone grasp their head in agony as rasp down the track!

Just what the Bean said: $75 muffler + $30 install.

Glad you like it... I sure am pleased with the sound level now. Sounds more agressive than just the Borla, but not unreasonably so. :D

Yes, BUT - this is not a "reversed glass pack" just a 3" perforated core (aka glasspack, although they're not called that anymore, lol, makes me feel old!) oriented NORMALLY - not reversed.

Random sells two that will fit in the place I indicated above. Shebam and I both have the 12" Random, and agree that it could be just a touch quieter. TheBean has (I think) the 18" Random model that will just barely fit, and I suspect would be better than what Shebam and I got. Since you've got a midpipe and not a HF cat (which is even louder) I would suggest you get at least the 18" Random.

However, you have the Greddy and all of us who've done this so far have the Borla catback. So I would suggest you got to a muffler shop and look at the piping while the car is up on the lift. Given that you can get 3" inner diameter perforated core mufflers in lengths from 12" to 24" (probably longer, too!), that have outside diameters from 4" to 6" you should be able identify a location and size that will fit. Just don't let the muffler guys talk you into anything other than perforated core 3" ID muffler... and they WILL probably try to sell you what they have in stock. Anything other than this will restrict your flow, and if you're gonna do that you might as well just put the stock exhaust and/or cat back on.

Hope this helps!

The Greddy is only 2.5" plumbing. So if he is using the greddy, he should be able to use 2.5"ID.

Slavearm

Yeah, that's true. In that case you should be able to get a lot less expensive muffler than the Random - it's one of the few in the right length with a 3" core.

14 or 18
 

Bean, did you get the 14" or the 18"?

Pretty sure he got the 18" unit.

How to fit 18" plus Borla?
 

Well, I obtained an 18" unit from Clay and took it to the guy who had installed my 14" unit and asked him to put it in instead. He said he was afraid to do it because there wasn't enough room without trying to attach it to a bent part of the pipe, and if he tried to cut on the straight parts and push them further apart it would push the pipes too close to some traveling suspension parts. It was the end of the day and he was kinda tired and he didn't want to take the chance, and I agreed. So --

-- can we confirm that anyone has added the 18" tertirary resonator to a Borla?

-- if so, what was the trick or technique and do you have a picture?

Thanks.

Been busy lately just sall this post.

I went with the 14" It's still a little to loud for my taste.

Aha -- so we still don't have an example of an 18" installation that fits, and after living with the 14" we appreciate it but all like a bit more noise reduction. As in other times of crisis, the initiative falls to intrepid Omicron to lead the way. (Unless I can find a braver or smarter muffler guy in the D.C. area than my Meineke guy -- any suggestions?)

Let your fingers do the walkin... look for a muffler shop that does performance exhaust systems. :)

How about you get an 18" spliced into one of the straight sections of the intermediate pipe?

Cheers,
Hymee.

Thought of that... problem is it would reduce ground clearance by a good inch.

Fair enough.

Cheers,
Hymee.