HUM­BLE RUMBLE

UN­DER­STAND­ING THE ART OF THE MUFFLE

NZ Performance Car - - Contents - WORDS: JADEN MARTIN PHO­TOS: NZPC AR­CHIVES

t’s all too easy to get car­ried away dur­ing the process of a big build, and find your­self en­gulfed in a se­ries of ex­pen­sive pur­chases that fill the en­gine bay and pack the sup­port­ing com­po­nents with crazy pieces of kit — hell, ask the owner of any car we’ve fea­tured and they’ll al­most al­ways tell you that’s the case. But while you’re wrapped up in all things power chasing, other im­por­tant pieces of the on­go­ing puzzle may be de­cided in pass­ing, or for­got­ten about com­pletely — ex­hausts be­ing one of the most fre­quent ex­am­ples. You may even over­look it in­ten­tion­ally, as it all be­comes too con­fus­ing: res­onate what? Muffle who? Dump where?

Is the mean­ing of any of this jar­gon im­por­tant? In short, yes, in­cred­i­bly. Don’t fall into the trap of buy­ing the first thing you see, and call­ing it a day. Not only does the muf­fler and res­onator combo con­trol your ex­haust note and level, it can af­fect your power lev­els, too. And of course search­ing for the per­fect ex­haust note can be­come an ob­ses­sion, and why wouldn’t it, given that ev­ery­one is par­tial to a dif­fer­ent sound — whether you like a mighty rumble, a raspier growl, or vir­tu­ally any­thing in be­tween, the af­ter­mar­ket ex­haust in­dus­try has come up with ev­ery con­ceiv­able com­po­nent de­sign to get your sys­tem note-per­fect, even be­fore you con­sider main­tain­ing or im­prov­ing per­for­mance. Hav­ing ac­cess to a huge pool of qual­ity pieces is sweet, but it can get pretty hard to select the right item for your ap­pli­ca­tion. To do so, it’s handy to un­der­stand ex­actly how it all works, so we called upon Brent at Adrenalin R and Kita at Manawatu Muf­fler Cen­tre for some in­sider knowl­edge. The first ques­tion you’ll ask is, what does a muf­fler do in my ex­haust sys­tem, and what is it made up of? That an­swer is pretty in­volved, so bear with us.

A muf­fler works to re­duce the sound that the en­gine pro­duces — as part of the process of emit­ting the ex­haust — to an ap­pro­pri­ate level. This is achieved by cut­ting the sound pres­sure emit­ted. Many OEM op­tions are made to sound OK, but are al­most al­ways re­stricted by ef­fi­ciency con­cerns, ease and cost of man­u­fac­tur­ing, and of course sound-level laws. The re­sult is that stock items are built to be con­ser­va­tive, and can re­strict your plan to in­crease power.

De­pend­ing on what style of muf­fler you’ve se­lected, it will achieve its aim in dif­fer­ent ways, as Brent from Adrenalin R told us. “Our muf­flers, which are com­pletely made of stain­less steel

Ro­taries are damn loud — as they don’t have a valve train to chop up the noise, they’re es­sen­tially de­liv­er­ing the di­rect com­bus­tion noise out the ex­haust

The qual­ity of the steel wool and how it is packed will de­ter­mine how long it lasts — in the right thick­ness and if ap­plied tight enough it won’t com­pro­mise the muf­flers longevity. When in­stalled in­cor­rectly, the pres­sure from the gas can push the wool down and al­low fi­bre­glass to es­cape

to avoid cor­ro­sion prob­lems, are the baf­fle-packed type. They con­sist of a stain­less steel baf­fle [the cen­tre part which gas flows through] which is then wrapped in stain­less steel wool, and it acts as a heat bar­rier. Ex­haust gases travel through the baf­fle into the stain­less wool, which is sup­ported by a fi­bre­glass pack­ing be­hind it. The pack­ing works to qui­eten the sound, while the steel wool ab­sorbs heat to pro­tect the pack­ing from ex­treme tem­per­a­tures”.

When it comes to the baf­fle-packed de­sign, there are two main types of baf­fles, as Brent ex­plains: “Per­fo­rated and lou­vred … per­fo­rated has holes in the baf­fle and acts as a pas­sive gas sys­tem, mean­ing it re­lies on the pres­sure of the ex­haust gas to push the gas through the holes into the pack­ing. This pro­vides less re­stric­tion and more flow for the same di­am­e­ter, and is reg­u­larly used in rac­ing, ex­treme per­for­mance, and high-pres­sure turbo ap­pli­ca­tions. The per­fo­rated de­sign is usu­ally louder, so con­sid­er­a­tions need to be made in terms of keep­ing it within le­gal lim­its.

“The sec­ond style, a lou­vered baf­fle, has a se­ries of flutes pro­trud­ing into the gas flow which scoops the gas out into the pack­ing and acts as an ac­tive sys­tem, it ac­tively catches the gas and forces it in the pack­ing.” This will re­strict it slightly, but is more suit­able for most ap­pli­ca­tions, and al­lows you to get away with a freeflow sys­tem for both good sound and power.

Kita from Manawatu Muf­fler Cen­tre ex­plained that when it comes to baf­fle-packed de­signs: “they will last a lot longer than fi­bre­glass-only packed op­tions, and they also have very lit­tle to no fi­bre­glass in them so the muf­fler it­self can ab­sorb a lot of the heat. This is a bonus for re­mov­ing con­den­sa­tion and mois­ture buildup from the gas, as glass-pack­ing can act like a sponge and ab­sorb the mois­ture … mois­ture and metal don’t go well of course and can rot out the internal struc­ture, com­pro­mis­ing your muf­fler as a whole”. Another de­sign which can be con­sid­ered is the cham­ber type muf­fler, as Kita said: “The cham­ber type is glass packed at ei­ther end with an empty cav­ity in the cen­tre. They are nor­mally found on older-style ve­hi­cles, things like car­bu­reted ap­pli­ca­tions, older straight sixes, V8s, sin­gle-cam en­gines, and those with smaller valve trains. But the de­sign does open the muf­fler up and won’t re­strict the flow as much, so hav­ing a cham­bered or straight­through glass-packed op­tion can re­move a lot of that re­stric­tion and in­crease ex­haust gas flow — more flow means the abil­ity to

Some peo­ple pre­fer the clean, deep sound of a per­fo­rated op­tion re­gard­less of where they in­tend to use it, but at the end of the day what­ever op­tion you select needs to be quiet enough come wof time or you’re in trouble

gen­er­ate more power. The down­side is that the fi­bre­glass is af­fected by heat and isn’t ideal for higher-temp ap­pli­ca­tions, such as tur­boback or ro­taries.”

As for what kind of noise you can ex­pect from the dif­fer­ent de­signs, there are a num­ber of vari­ables in each en­gine that will change the sound’s char­ac­ter out of the muf­fler, and it’ll be af­fected by dif­fer­ent res­onators or cat­alytic con­vert­ers. Brent said, “Some peo­ple sim­ply pre­fer the sound of the per­fo­rated baf­fle and will put them on ev­ery­thing — it pro­duces a deep, clean sound as it’s not dis­rupt­ing how the gas trav­els … at the end of the day we al­ways try achieve what the cus­tomer wants, while keep­ing it within the ac­cept­able deci­bel level for a war­rant. Lou­vered baf­fles pro­duce a more muf­fled note, and the spi­ral de­sign helps to spin the gas, which dis­rupts the way it trav­els with­out dis­rupt­ing the flow, thus re­duc­ing the noise that comes out.

Another thing to think about is the po­ten­tial ef­fects of your choice of muf­fler on your over­all per­for­mance, and how to op­ti­mize the flow for the best pos­si­ble re­sult. Kita says, “Some form of re­stric­tion is al­ways to be ex­pected when it comes to muf­flers, but it’s so min­i­mal that the per­for­mance loss is neg­li­gi­ble and doesn’t re­ally fac­tor into it. We’ve had cus­tom built ex­am­ples dy­noed, mainly the race ap­pli­ca­tion ones, and there is lit­tle to no dif­fer­ence. By hav­ing ef­fec­tive in­ter­nals that cut the re­duc­tion, you shouldn’t see much or any dif­fer­ence.” Brent agreed, and said that when the right sys­tem is in place the dif­fer­ence shouldn’t be no­tice­able. He tells us, “It boils down to the en­gine in ques­tion, some will be op­ti­mal with a short pipe off the turbo, while a ro­tary will want a full taper sys­tem that starts off at one size and slowly ta­pers out — but that is al­ways far too loud to run legally. Like­wise drag cars run straight off the head­ers, al­low­ing more fuel in and less re­stric­tion, but again not many places al­low this. So you work to get it as close to that op­ti­mal point as pos­si­ble whilst still be­ing le­gal.”

“Some form of re­stric­tion is al­ways to be ex­pected when it comes to muf­flers but … by hav­ing ef­fec­tive in­ter­nals that cut the re­stric­tion, you shouldn’t see much or any dif­fer­ence.”

So how do you go about se­lect­ing the right muf­fler for your ap­pli­ca­tion? That’s where it gets a bit trick­ier. There are hun­dreds of op­tions avail­able in a va­ri­ety of sizes, so the first step is to select one that will fit the space avail­able, as al­though a larger body and length may help re­duce the noise level while main­tain­ing flow, if it doesn’t fit, it doesn’t fit. Af­ter that it’s a mat­ter of think­ing hard about what you’re try­ing to achieve. Are you up­grad­ing to a sim­ple re­place­ment for lazy street driv­ing, or build­ing some­thing from scratch that aims for the best per­for­mance pos­si­ble? This plays into what size pipes you’ll choose, along with the re­quired con­fig­u­ra­tion and tip sizes, etc. Brent said: “If you’re try­ing to get the ideal V8 muf­fler, you’ll be look­ing to use a cor­rectly sized cham­ber type. Some­thing that will go straight through to the rear cham­ber, cross over and then go out, which in turn helps with the back pres­sure that the V8s re­quire. Like­wise, a ro­tary muf­fler is look­ing to get the gas out as quick as you can, the less re­stric­tion the bet­ter, but as they have no valve train to chop up the noise, they can be ex­tremely loud. It’s es­sen­tially de­liv­er­ing the di­rect com­bus­tion noise out the ex­haust. Run­ning a straight-flow sys­tem on a nat­u­rally-as­pi­rated ro­tary, us­ing two torque cham­ber per­fo­rated baf­fle res­onators will pro­duce a clean sound. When the gas goes through the cham­ber it has room to ex­pand, the next pulse hits and that gas cre­ates a small amount of back pres­sure with­out re­stric­tion, then out of there into a lou­vered muf­fler gives the best of both worlds, clean sound with the most noise re­duc­tion.”

Ob­vi­ously other things in the sys­tem also af­fect muf­fler se­lec­tion, such as a cat­alytic con­ver­tor on newer ve­hi­cles. While most peo­ple opt to delete these where pos­si­ble, some may not be able to be deleted with­out a lot more has­sle, so will re­main in place. In this in­stance you have a few choices, and as Kita ex­plained: “Cats are very re­stric­tive by them­selves, so they are of­ten deleted and re­placed by a res­onator to keep noise down. In some in­stances they are fit­ted with a sec­ond oxy­gen sen­sor which is fed to the ECU, and the only way to delete the cat is to turn the sen­sor off, which isn’t al­ways easy — here we’d rec­om­mend up­grad­ing to a high-flow cat in­stead. It acts sim­i­lar to a muf­fler and we’ll treat it as such, know­ing that the cat will re­duce noise, and the type of muf­fler used can be based around that. It’s im­por­tant to de­cide on what course of ac­tion you’ll take with the car be­fore in­stalling a muf­fler, as the muf­fler rec­om­men­da­tion is go­ing to be dif­fer­ent.”

So to wrap up the whirl­wind of in­for­ma­tion, a lot more con­sid­er­a­tion needs to be paid to your muf­fler and re­lated com­po­nen­try than most peo­ple re­al­ize. The an­swer on what type, where, how large, and how many all lies within your spe­cific ap­pli­ca­tion and how much you’re look­ing to spend. All in all, con­sult the peo­ple in the know and seek the cor­rect ad­vice when mak­ing your se­lec­tion — you’ll end up with a bet­ter re­sult, and even save your­self a bit of coin, too.

Whether your sys­tem has a cat­alytic con­verter or not plays a part in muf­fler se­lec­tion too, as they take a hell of a lot of sound out. Mean­ing you can have a more ag­gres­sive muf­fler de­sign

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