Quiet Muffler that will not Restrict ZE Performance?

Overclock · Post by **Overclock** » March 30th, 2005, 10:25 pm

I know muffler debates are all over these forums but there seems to be little discussion on a quiet solution for ZE's.

I have a huge Reactive muffler on stock exhaust and the noise inside the car is deafening. Waking up my girlfriend's parents when I drive her home at night is not a good thing either.

I want max quiet without restricting the ZE.

Recommendations?

DavidOS · Post by **DavidOS** » March 30th, 2005, 10:27 pm

Get a resonator pipe put in and a really good magnaflow exhaust will work well.

jschrauwen · Post by **jschrauwen** » March 31st, 2005, 1:35 am

I agree. My Magnaflow isn't really any louder than the stock exhaust but has a bit of a deeper, throatier sound. The sound level all the way up the rpms is still about the same as stock and hardly noticeable after 3,500 rpm. A good compromise I think.

johnnyb · Post by **johnnyb** » March 31st, 2005, 4:26 pm

go to any performance exhaust shop man they have a wide variety of quiet performance mufflers for you to choose from.

Overclock · Post by **Overclock** » April 1st, 2005, 12:16 am

Alright, what is considered a really good Magnaflow? I surmise they have more than one model.

Where do I get a resonator pipe? Brands, models?

tatsu · Post by **tatsu** » April 1st, 2005, 11:49 am

As previously discussed on this forum, to get a quiet exhaust without too much restriction, you need to install the largest, longest, "straight-through" design (single-pass, not baffled, perforated core) rear silencer and pre-silencer (AKA rear muffler and resonator) you can fit.

Unless you have a turbo/supercharger, you will probably want 2.25" diameter throughout. You might get a tiny bit more peak HP with a 2.5" system, but you would lose some low to mid-range torque. Also, make sure that all of the tubing in your exhaust system is mandrel-bent to ensure minimum flow restriction. Mandrel bends maintain the tubing diameter throughout the bend, unlike crush bends which (as the name implies) crush the tubing down to make the turn.

For a look at a good muffler design, check out this page from Magnaflow's website. This is a very good illustration of a perforated core, and a "straight-through" design. Magnaflow calls this "Wide Open Performance", but other exhaust manufacturers also offer similar designs.

For a "resonator" what you are really looking for here is a pre-silencer - basically another silencer fitted upstream of the rear silencer. Magnaflow and others offer round-body units in varying lengths and inside diameters that are perfect for this - get the longest one you can fit between the catalytic converter and where the exhaust tubing first takes a bend to make its way up and over the rear suspension. All of Magnaflow's units are 14" long, by the way. If you can fit something with a larger diameter as well, it will be that much quieter. Here are my recommendations for a Magnaflow part:

Part # 14415 (4" diameter, 2.25" inlet and outlet, 2.5" core)
Part # 14615 (6" diameter, 2.25" straight through)
Part # 14715 (7" diameter, 2.25" straight through)

These units can be found here. The 6" or 7" units would be the preferred choice if you can fit them, but they may be too big around to allow sufficient clearance to the body and the ground - make sure you take some accurate measurements before buying!!!. There is also another 4" unit with a 2" core (Part # 14445) which should be quieter, but I wouldn't recommend that from a performance perspective because it will be more restrictive.

For a rear silencer, you will need something that has its inlet and exhaust offset opposite from each other - meaning the inlet should be up high on the front of the silencer body and the outlet should be down low on the back. This will allow you to avoid a sharp bend in the tubing after the rear suspension to get into the silencer, and is the same layout Mazda used with the OE exhaust. The unfortunate thing about this layout is that none of the major manufacturers make a universal unit with twin outlets with that kind of offset, so you are stuck with either using a single tip, or a Y-type twin-tip to simulate twin outlets with a single outlet exhaust - for some people, this is no big deal. Here are the Magnaflow parts I would recommend:

Part # 14335 (4x9" oval, 14" long body, 2.25" straight through)
Part # 14365 (4x9" oval, 18" long body, 2.25" straight through)
Part # 14235 (5x8" oval, 14" long body, 2.25" straight through)
Part # 14262 (5x8" oval, 18" long body, 2.25" straight through)

The 18" long units might be a tight fit - an OE replacement silencer body is only 15" long, so again, make sure you measure before buying!!!

If you really want true twin tips and are willing to possibly sacrifice a bit of performance with the sharp bend necessary to fit a non-offset silencer, here are some other universal options from Magnaflow:

Part # 14220 (5x8" oval, 14" long body, 2.25" inlet/twin 2" outlets)
Part # 14218 (5x8" oval, 14" long body, 2.5" inlet/twin 2.5" outlets)
Part # 14258 (5x8" oval, 18" long body, 2.5" inlet/twin 2.25" outlets)

Again, watch out for the length on the 18" long unit - measure a dozen times before you spend your hard-earned cash!!!

Magnaflow also offers some "mirror-finish" polished universal units with pre-installed tips. They are all 2.25" inlet diameter, with 14" long bodies, but NONE of them have the offset design. You can check them out here. The only ones I would recommend for quiet(er) power would be the 5x8" ovals or the 6"/7" rounds, although the 7" rounds might have some ground clearance issues.

Bear in mind also that you can fit similar tips to the universal, single-outlet, oval body silencers with the proper offsets - this would be the preferred choice from a performance standpoint. Magnaflow has their really nice double-wall tips listed here - they all have 2.25" inlets, with one exception (a really ricey looking 2.5" inlet "Tanabe" style 4.5" single round tip). Another thing to note is that the Y-style twin tips are 10" long overall, so some careful placement of the rear silencer (I.E. just about as far forward as possible) will be necessary to prevent the tips from sticking out too far.

Hope this helps!

jschrauwen · Post by **jschrauwen** » April 1st, 2005, 7:40 pm

Tatsu, much impressed. This is definitely going in to the save file, many thanks.

MarkMoore · Post by **MarkMoore** » April 2nd, 2005, 9:07 am

i just got a new custom exhaust system... got a high flow cat, oval 5 x 8 dual tip stainless steel muffler, and two double wall stainless steel tips welded on--all made by magnaflow...

my impressions: well i just got it back yesterday, and i wasn't really focusing on my exhaust sound that much but instead the fact that my car kept on stalling out after i paid my mechanic to fix the problem for me which kinda got me frustrated (it might just be coincidence, but i think it's the same problem)... but just about 5 minutes ago i was outside and started up the mx and gave a good listen to my new exhaust through the whole RPM range and while it was idling, and i must say that the sound is very good... just one thing---it's too loud for me.... soooo, when my mechanic takes back my car to take a look at the stalling problem, i think i'm gonna have him put the biggest resonator that will fit in there to quiet it down a bit without robbing my car of the great sound it now has.... kinda stupid, i know, to have an exhaust completely built then change it right away, but i really didn't know how loud it was gonna be, and i'm really not one who wants the attention of everyone w/in 4 blocks of me to know that i have a loud car.... but that's just me, it doesn't make me feel cooler

having everyone's attention..

but u can't go wrong w/ magnaflow, i'd just suggest a resonator lest u fall to the cult of rice-r-oni...

Overclock · Post by **Overclock** » April 2nd, 2005, 12:07 pm

Mark, let me know how that resonator pans out for you. I'm pretty much decided on going Magnaflow but am curious to see how quiet you get yours.

Also, feel any noticable performance difference with the new exhaust?

MarkMoore · Post by **MarkMoore** » April 2nd, 2005, 6:36 pm

Overclock wrote:Mark, let me know how that resonator pans out for you. I'm pretty much decided on going Magnaflow but am curious to see how quiet you get yours.

Also, feel any noticable performance difference with the new exhaust?

yea, i don't know if i mentioned this before, but i went w/ 2.25" exhaust, and then it changes to 2.5" in order to fit the inlet pipe of my muffler, so for all intensive purposes it's a 2.25" 'cept for less than a yard it's 2.5" (because i changed my mind at the last minute and wanted 2.25", and this all occurred AFTER i had purchased all of my components to be 2.5", so my mechanic said he changed the pipe diameter right in front of the muffler to 2.5" to be able to better weld it to the muffler--that is if i'm understanding him right

)...

as for the performance, once again, i was so frustrated that my car wasn't working, i was just focused on gettin my car home (my mechanic lives 35 mins away since he's really a friend of a friend and gives me a great deal on labor charges)... but the few moments i did bother to notice, it did definitely feel like it was a lot less restrictive, and it definitely smooths things out real nice... but of course i'm runnin' a k8, so i wasn't expecting anything crazy as far as hp, but i'd guess i gained a few due to the less restrictive exhaust path... but w/ a ze i'm sure the new exhaust would be much more needed and would give more of a hp gain, cuz obviously bigger engines NEED bigger pipes... i am plannin' to upgrade to a ze, in which case my new exhaust will have helped me out a lot more than it did w/ my current k8...

tatsu · Post by **tatsu** » April 3rd, 2005, 6:07 am

Since I was cleaning up my garage anyway, I threw our GS up on the jackstands and took some measurements.

The body of the stock pre-silencer/resonator is 4" in diameter and about 8" long. There is a heat shield directly above this area, with the handbrake mechanism above that. This, along with the fact that the bottom of the stock 4" unit is basically in line with the lowest point of the unibody leads me NOT to recommend anything larger than 4" in diameter as a replacement.

With that in mind, my only recommendation for a pre-silencer/resonator would be Part # 14415 (4" diameter, 14" long, 2.25" inlet/outlet with 2.5" core).

As far as diameter/height/ground clearance for the rear silencer goes, you could fit any of the Magnaflow units, but the 4x9" oval offset silencers might be a tight fit up top if you tried to maintain the stock amount of ground clearance (which I would recommend, as that keeps the exhaust outlet in nice and close to the body). Due to this limitation, I would only really recommend the 5x8" oval units (NOT the 4x9" oval units) if you are looking to use an offset design.

There is just barely enough room between the rear suspension and the rear of the unibody for an 18" long rear silencer, but it may rub when the exhaust moves backwards on its hangers under hard acceleration. An 18" long silencer would limit you to tips no more than 6.5" long, or they will protrude beyond the plane of the lower rear bumper (which, in my opinion, looks silly).

If you ran a 14" offset rear silencer, there would be plenty of room for whatever tip(s) you desire if it was mounted with the front edge of the silencer body in the stock position. There is sufficient room for tips between 8.5" and 10" in length - the Magnaflow Y-type twin-tips all fall within this range.

If you want to run shorter tips (most of the Magnaflow single tips are 7" long), you would need to either mount the rear silencer 1.5" to 3" further rearward, or have a 1.5" to 3" tailpipe added between the silencer and the tip. The reason for this is that if the tip ended much further forward, exhaust gases could become trapped within the rear bumper cover, and eventually find their way back into the passenger compartment - carbon-monoxide poisoning, anyone? I thought not...

If you ran a 14" long, non-offset, true twin-tip silencer, you could (and should) mount the silencer 3" further rearward than stock to lessen the severity of the bends required for the over-axle pipe to enter into the silencer. By happy coincidence, all of the Mirror-finish units with pre-installed tips are 5x8" non-offset ovals with 14" long bodies, and it is significantly cheaper to buy those units than to buy the plain silencer and add the tips.

If you want to go for a stealthy factory look with no fancy tips, you could get Part # 14220 (5x8" non-offset oval, 14" long, 2.25" inlet/twin-2" outlets) and just have some extra length added to the twin-2" outlets.

Other than that option, with all of the above in mind, here are my recommendations for Magnaflow rear silencers:

Part # 14335 (5x8" offset oval, 14" long, 2.25" straight through; use with any Magnaflow single or Y-type twin-tip)

Part # 14815 (5x8" non-offset oval, 14" long, 2.25" inlet with pre-installed twin-3" diameter/7" long round tips)

Part # 14816 (5x8" non-offset oval, 14" long, 2.25" inlet with pre-installed twin-3.5" diameter/7" long round tips)

Part # 14827 (5x8" non-offset oval, 14" long, 2.25" inlet with pre-installed 4" diameter/7" long single round tip - a bit ricey for my tastes...)

Part # 14830 (5x8" non-offset oval, 14" long, 2.25" inlet with pre-installed twin-3.25"x2.5" oval/7" long tips)

Part # 14833 (5x8" non-offset oval, 14" long, 2.25" inlet with pre-installed twin-2.75"x2.5" square oval/7" long tips)

While I'm at it, Magnaflow also carries some high-flow catalytic converters - the one we want is Part # 53005 (2.25" diameter, 3-way catalytic converter with no O2 sensor mount).

Well, that's it for me, I'm EXHAUSTED...(yikes, that was a bad pun, but what do you expect at 2:00 AM?)

Any questions, please PM or e-mail me. Oh, and no, I don't work for Magnaflow - I just like their products.

Overclock · Post by **Overclock** » April 3rd, 2005, 12:35 pm

I'm impressed tatsu, you really seem to know your stuff.

I'm fairly convinced to follow your directions on what to install on my car. I have a concern about the high flow cat however. Will it create more noise than the stock cat? I know that catalytic converter plays a large part in how much noise comes in from the front of the car. I had one begin to die on me and the noise of a poorly functioning cat is even worse than the ridiculous Reactive muffler I have on my car at the moment. At least when it's the muffler the noise comes from the rear of the car and not directly underneath the driver's seat.

tatsu · Post by **tatsu** » April 3rd, 2005, 4:14 pm

The high-flow cat should have little effect on the sound as long as it is properly installed. If anything, the tone might be a little lower due to the reduced restriction, but the volume should not be affected much.

The worst I ever experienced was in my friend's 84 GTI, when his exhaust separated from his long-tube European downpipe (right below the shifter). VW's are pretty boomy to begin with, but this thing was UNREAL - it was SO loud you couldn't even think, and the vibration from the sound waves was enough to make your vision blurry. We had to drive for an hour like that to get to his house! Youch...

mazdubber · Post by **mazdubber** » April 3rd, 2005, 5:28 pm

What makes you think that 2.25" exhaust is a better option than 2.5" when the guys on Probetalk that are making the most power out of N/A ZE's are running a 2.5?

Yoda · Post by **Yoda** » April 3rd, 2005, 10:16 pm

The only way to lower sonic energy without loosing volume of gase flow is to cool and reduce the exhaust gases as fast as possible. The most effecient way of doing this is have the exhaust gases enter an expansion chamber(s). In the process of occupying the larger space of a chamber(s) the exhast gases loose thermo energy, become denser, and loose velocity which lowers the SPL of the exhaust. There is a benefit to this process in that the expanding gases in the chamber(s) create a vacuum in the pipe pulling more gases out of the engine than could flow if exhaust was a continuous diameter which equals more HP. A good chambered resonator and chamber mufflers goes along way to reducing sonic energy and increase HP across the board at the same time. On my exhaust I had a custom made 4 chamber resonator made for me within a section of 4" pipe running out into twin 2" inlet semi chamber 7 X 16 round mufflers. The tips are also resonated with an acoustic damping material. This goes a long way to reducing cabin resonance with and exhaust and lower the sound of the exhaust to a low frequence that may. On my old KL-DE HP went from 156 to 162 at the wheels over a straight through muffler but the biggest gains were around 4000-5200rpm were it make the makes the biggest impression on the driver next to you. I have never dyno'd the KL-ZE currently in the car but it is a lot quieter that the old DE.