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Motorcycle Exhausts 101

After this, read Motorcycle Exhausts 201!



Uncle Loomis - Merchandising

PUBLISHED: APR 20, 2013

Why would a rider buy an exhaust? Are they something riders need? Something we want?  Are they easy to install? Do I need one?

All of those questions have a multitude of answers. For the purposes of this ‘101’ tutorial, we’ll use general and specific examples, but we’re going to focus exclusively on four-stroke engines. Unless you have a fairly old street machine or a dirtbike, odds are very good you have a four-stroke engine. Exhausts for the two types of engines are pretty different, so we’re going to zero in on four-stroke exhaust, the type of exhaust most folks are going to need for street riding.

Why does my bike need an exhaust system in the first place?

Motorcycles are fitted with exhausts for a few reasons:

  • They route combustion gases away from rider and passenger - You don’t want to suck down a carbon monoxide cocktail, right?  And your passenger probably does not want soot on her jeans or a burn on her foot.  Exhaust pipes move exhaust to a more convenient place!
  • They muffle noise - Putting a muffler on an engine is a wonderful way to make it reasonably quiet.  If you’ve ever been to the track, dragstrip, or your local muffler shop, you have some idea of how face-meltingly LOUD a vehicle with no exhaust is.
  • They help the engine perform better - believe it or not, bolting a simple tube on a motor can actually help it run lots better.  There’s an amazing body of research dedicated just to exhaust in fields like thermodynamics and laminar flow, but suffice it to say that the right exhaust can help you go faster

Why would I want to replace my factory system?

So... your bike probably came with an exhaust system already on it.  What would make someone take a perfectly good stock exhaust system off their bike?  There’s a bunch of good reasons to replace an exhaust:

  • Goin’ fast! - Remember, the OE manufacturer had to meet a budget.  That means that they might have been unable to produce the best motorcycle exhaust pipes possible for your bike at the price you purchased it for.  They may have used a simpler or easier-to-manufacture design rather than the best design.  They are constricted by emissions regulations, and by having a broad customer base who may all be doing different things with their bikes, leading to an exhaust that may be a compromise.
  • Goin’ on a diet! - Replacing, for example, a big, steel dual exhaust system with an aftermarket titanium unit with a single short unit can yield fifteen pounds or more of shed weight - depending on your bike, that could be five percent of the total machine!  When it comes to handling and performance, dropping weight in the right places can be as good (if not better than) increasing horsepower.
  • Goin’ to save some money! - Dollar for dollar, it’s hard to replace a component that has as big an effect on the look, sound, AND performance of your bike.  Very few aftermarket parts do so much for such a low cost.  Exhaust isn’t necessarily cheap, but it is an excellent value.
  • Goin’ deaf! - Depending on what you ride and what type of exhaust you install, you can really change how your bike sounds.  A small-displacement metric cruiser typically experiences an auditory change that could be characterized as going from a sewing machine to a fire-breathing monster.  Mildly buzzy sportbikes turn into an unstoppable cacophony when ‘uncorked’.  While there are levels of sound available from quite tame to vision-blurring, most motorcyclists will tell you that the ‘bark’ an aftermarket exhaust adds is pleasurable.

How do aftermarket performance exhausts actually improve my bike’s performance?

Your engine can be thought of as a pump, moving air and fuel (in a precisely metered recipe - more on that later) into itself, and moving burned air and fuel (exhaust) out.

There are a few ways of making the engine do more work - but most have some drawbacks.

  • Make the engine go faster - this is what you do every time you twist the throttle.  Most engines are limited in speed (their redline) by the valvetrain.  Speeding up the engine requires stronger engine internals due to the increased heat, friction, and speed.  Typically, this is a pricy and labor-intensive, and some engine styles (like big-inch, long-stroke V-twins) respond poorly to this approach, because their power is not made high up in the rev range, and critical engine parts bear heavy loads.
  • Make the engine bigger - this is what’s done when an engine is bored or stroked.  Typically involving stronger internals, this is another labor intensive process that can thin out the bulkiest of wallets.
  • Make the engine hold more air and fuel - this is what a turbo, nitrous oxide, or a supercharger does.  Instead of making the engine bigger, forced induction physically shoves more burnable matter into the same size engine by compressing (pressurizing) the air.  Again, the enemies here are heat, stress, and cost.  All three will be plentiful if this method is chosen.
  • Make the engine more efficient - this is the easy and affordable way to pick up a few extra ponies.  In terms of ‘efficiency’, we’re not talking about your fuel mileage, but rather, how good your engine is at turning air and fuel into horsepower without producing waste products like heat.  This approach is usually not labor-heavy or too expensive on a factory engine, but it is limited in its scope - you will not be able to pick up a hundred horsepower by bolting stuff on to your engine.  The idea here is to unlock just a little more power by making the engine’s intake and exhaust less restrictive, limiting power losses by reducing the work the engine must perform when it draws in air and fuel and expels exhaust gases.

What type of exhaust should I get?

Excellent question!  What type of riding do you do?  A heavy fella who carries loads of camping gear on his Harley Bagger is going to want a vastly different exhaust than someone tearing up the track on a stripped-down CBR. 

Motorcycle Exhaust systems typically come in one of two types:

  • Mufflers only (also called slip-on or bolt-on systems) - this type of exhaust retains the factory headpipe(s), and replaces just the muffler.
  • Full system - this type of exhaust replaces everything from the engine block to the back of the bike.

Most slip-on systems are typically (not always, but usually) designed to be the only thing that gets changed on your bike.  The performance boost is not as great as a full system, but initial cash outlay is reduced, and installation is typically quite simple.

Most full systems need fuel management changes to work correctly.  This will typically entail a jet kit for a carbureted bike, or a fuel controller for a fuel injected motorcycle.  This type of exhaust system is typically more complex to install than the mufflers-only system, but the reward is a greater power gain, and often a more aesthetically pleasant exhaust system.

To correctly select an exhaust pipe, we think several things are important.  First, figure out your final goal with the bike.  If you just want a little more rumble and a bit more pep, an inexpensive slip-on may be the way to go.  If, however, you are planning on future headwork, camshaft changes, or different carbs, a full system will allow you to take complete advantage of all the aftermarket parts/work.  Each modification, ideally, will be made with the other modifications in mind.  A properly-thought-out engine modification plan can make great gains with fairly modest expense.  Similarly, ill-chosen parts can often cost lots of money and work poorly together - if you need help determining what parts ‘play well’ together, get in touch with us!

If you are on a budget, but have lofty goals, some exhaust manufacturers offer systems that are ‘modular’; that is, you can buy a slip-on muffler, and later, when budget and other modifications dictate, you can then replace the factory headers, but retain your slip-on muffler.  Not all manufacturers do this, so if you think you might hot-rod your bike down the road, this is a great way to get your feet wet without breaking the bank - but you’ll retain the option to keep building from your existing platform.

What style should I buy?

There are many, many exhausts to choose from.  Here are some factors you might want to think about.

  • Entrance/exit - usually characterized as the number of inlets and outlets, style, bike type, and engine play into this choice quite a bit.  Often, a factory 4-into-2 exhaust will be made aftermarket as a 4-into-1 system because the exhaust can be moved almost as quickly through the less restrictive system and relieve your bike of the excess weight of the extra muffler.  Some engine types ‘prefer’ one style over another - V-twins, for instance, typically give great torque gains when 2-into-1 exhausts are used.  Some research or a call into our Gear Geeks are encouraged to help you get an exhaust that will meet your needs..
  • Material - titanium and carbon fiber are becoming popular due to their low weight.  However, their cost can be prohibitive.  Aluminum offers some benefits of weight loss and lower cost.  Stainless steel is ever-popular due to cost and durability.  Chromed steel is often prized for its beauty and longevity.  How fastidiously you maintain your bike’s appearance, and how you want to look are going to play into your selection of material, as well.
  • Outlet type - Maybe a big, carbon fiber can is your look.  Maybe you like old-timey cocktail shakers or cigar mufflers for your Brit bike.  Maybe goose-cut turn-outs or fishtails are your style. Some aftermarket exhausts - for cruisers especially - are capable of being fitted with a variety of easily swappable tips to give a different look.  Your point of termination from your exhaust is often a point of visual importance, so pay attention to what you think looks good!

Should I run drag pipes/open exhaust?

Maybe.  If you’re at the drag strip or track, probably.  If you’re anywhere else... probably not!  Realistically, ‘open’, or unmuffled pipes make horsepower high in the rev range, where the engine is expelling the highest amount of exhaust.  However, because they do not promote good velocity in lower portions of the rev range, they tend to be a poor choice for street use.  Tuning the bike is very difficult with drag pipes, and almost all open exhausts leave weird ‘flat spots’ where power is delivered erratically, or can even decrease! 

If you’re honest with yourself, you’ll probably find that wide-open throttle most of the time is not really how you ride on the street.

There are a great many federal, state, and local laws in America, and typically they mention unmuffled pipes as being problematic - again, every place is different, but by and large, having at least a muffler is usually the minimum exhaust requirement you’ll need to meet for most vehicle inspections.

The fact is that the exhaust manufacturers spend quite a lot of time and money developing an exhaust product that will lend you the most horsepower and torque for your particular motorcycle without being overly obnoxious.  Loads of dyno-tuning and testing back up their product.  It is pretty rare to achieve a better all-around exhaust for street use than the ones the big players in the exhaust game have developed.  Keep in mind that most of them do significant exhaust acoustics testing - they know you want your bike to sound nasty, and the time-tested exhaust manufacturers have had many satisfied customers over the years.  Unless your bike is way different than a stock engine, a bolt-on exhaust is probably just what you need for a little more oomph!

Will my bike pass inspection with an aftermarket motorcycle exhaust pipe?

Excellent question.  Your best bet is to call your local law enforcement provider to determine as much - and they may direct you to a local shop or a government-run inspection agency.  The reason for such an answer is that there are many state and local regulation regarding emissions output, volume, and safety inspections.  Typically, in most states, a full or slip-on exhaust that has mufflers and does not remove a catalytic converter is OK providing it is not particularly loud.  However, that’s a rule of thumb, NOT a hard-and-fast rule.  Call your local police department, DMV, or motorcycle shop!

How loud will it be?

Well, that depends on a few things.  Nearly every aftermarket exhaust is louder than the factory exhaust.  If you purchased an aftermarket Harley exhaust, it will likely be fairly loud - some of the performance gain depends on not needing to silence the bike.  If the exhaust is too loud, some manufacturers offer quieter baffles that you may install to bring the volume of the bike closer to stock.

If you purchased an exhaust for a sportbike, there is often a removable baffle in the tip of the muffler (commonly referred to as a dB killer) that can be removed or installed for similar manipulation of sound levels.  Performance is usually unaffected by the presence or lack of these baffles.

I heard I need to change my fuel delivery setup, too - is that true?

The answer to that question depends on a lot of things - what kind of bike you have, what kind of exhaust you have, and how you want your bike to behave!  As a general rule, most slip-on or ‘mufflers only’ exhaust systems do not need to have the fuel delivery altered, but even a bone-stock factory motorcycle will benefit from fuel delivery adjustments.

If you are purchasing a full exhaust system, most manufacturers STRONGLY recommend fuel system changes.  Effectively, the exhaust helps the engine breathe better, but without adding more fuel to compensate for the greater ease with which the engine gets air, the ratio of fuel to air becomes imbalanced.  That condition is known as a lean condition, which can make the temperature of the engine catastrophically high.  Couple this situation with the fact that recent EPA regulations have been causing manufacturers to set bikes up quite lean from the factory, and a plan for poor performance and longevity is afoot!

Typically, ‘richening’ the air fuel mix (decreasing the air-to-fuel ratio) is done by purchasing a fuel controller for a fuel-injected motorcycle, or jet kits for carbureted bikes.  A dyno run/tuning session is often in order, so if you are not an experienced tuner, being aware of those costs as well will keep you within your performance budget.

Before you purchase your exhaust, you might want to consider a few things:

  • Engine modifications work with each other - the sum of carefully selected parts usually leads to greater performance gains than any part offers individually
  • Modifying your engine is very personal choice.  Changing your bike to perform differently than the factory intended is possible and often desirable, but the changes must be made thoughtfully.
  • If you do not want to change your fuel delivery method, you may be best served by a simple slip-on system made by a manufacturer that does not require a fuel system change.

How do I keep my pipes from turning different colors?

The honest answer here is that you don’t.  All pipes discolor to some degree due to heating and cooling, the presence of environmental contaminants like tar, oil, and road debris, and the material the exhaust was created from.  Stainless pipes, for example, turn gold - there is nothing wrong with this; it is a property of the alloy.  Cruiser pipes often ‘blue’, especially near the heads.  Pipes ‘bluing’ are a result of how the bike is running, not a defective finish.  Camshaft choice, engine timing, carburetion, and other factors all affect exhaust temperature, the biggest determinant in keeping exhaust the color it was intended to be.

These are some of the best ways we at ZLA know of to keep exhaust looking brand-spankin’ new:
Make sure your bike is in a good state of tune - properly gapped spark plugs and proper jetting go a long way to keeping pipes looking great.
Buy double wall pipes - Effectively a ‘pipe-within-a-pipe’, the outer visible pipe never achieves the high temperatures the inner pipe does, thus leaving it stain-free.
Buy pipes with extensive heat shielding - Some brands of exhaust come with heat shields so voluminous, they appear to be the exhaust pipe.  However, since there is a layer of cool ambient air between pipe and shield, the shields never attain the temperatures the inner pipe is subject to.

A word about ‘wrapping’ your pipes with fiberglass tape:  Originally seen on the dragstrips to keep exhaust temperatures high to improve exhaust velocities out of the exhaust, pipe wrapping has become popular on the street due to its unique look.  It can and does tend to hold moisture near the metal, thus speeding the oxidation process.  Most manufacturers consider wrapping pipes to be ‘abuse’ and typically do not warrant problems stemming from wrapping pipes - do it at your own risk!

How hard is it to install motorcycle exhaust pipes on my bike?

Well, it depends on some things.  What do you ride on?  How good a ‘wrench’ are you?  What kind of system are you installing? 

The answers vary greatly.  We’ve put bolt-on exhausts on a bike and had it running and riding in under twenty minutes, whereas some bikes require considerable time simply to remove the body panels necessary to gain access to the exhaust. 

Consider your mechanical aptitude and understanding of the exhaust system and the related systems requiring disassembly to access the exhaust.  Take stock of your tools on hand, and your ability to follow directions. 

If any of these seem like obstacles, don’t be afraid to call us and ask for a recommendation on how to attack your specific bike and pipe combo.  Sometimes, an install from a competent shop for a fair price can give you peace of mind, while relieving you of any possible problems from an exhaust job that was tougher to tackle than originally estimated.

What about staying legal? And how about C.A.R.B.? Who are they? Can I only use a certain type of exhaust?

Staying legal can be tricky. Ultimately, it’s up to each rider to make sure we are following the laws of the countries, states, and municipalities we live in, ride through, and visit. C.A.R.B. is the California Air Resources Board, and while not all riders fall under their jurisdiction, the laws they promulgate frequently have far-reaching effects for nearly all North American riders. If you’re interested in finding out a bit more, our Exhausts 201 article is an in-depth analysis of current emissions and noise pollution laws. We think it’s got some good insights on how to select products that keep you on the right side of the law.

What do I need to know before I order?

A few things! 

  • Your year, make, model, and engine displacement are imperative - guessing here often leads to the wrong parts being sent out.
  • An exhaust system usually includes just the pipes.  Re-using gaskets works sometimes... but not every time.  Fresh gaskets are always a good idea to get coming from your OE dealer.
  • Hardware is another component that often suffers, as are oxygen sensors.  Typically made of mild steel, hardware can rust, bind up, or break due to the heat cycling it receives over the course of its life, and oxygen sensors are often damaged to the point of unusability upon removal  Be prepared to find or purchase parts that may break while you are working, or purchase them beforehand.  A word of caution - oxygen sensors can be removed with normal wrenches, but specially-designed sockets and wrenches exist - they typically extract sensors unbroken with a much higher degree of reliability than standard hand tools.  Consider one!
  • Once an exhaust shows signs of being mounted, it is not typically returnable.  We do not send out exhausts that have been installed - consequently, we cannot take them back in such a state.
  • You need to know how an exhaust will work with your bike.  An exhaust system is an aftermarket modification.  They are usually made for stock motorcycles - if your rig deviates from stock, the onus of responsibility for determining if two components will ‘play nicely’ together must rest with you - you know what is on your bike!  If you have a question or concern; call us.  If we don’t know, we’ll find out.
  • In a similar vein, some exhausts require modification to your motorcycle.  You may need to relocate components such as oxygen sensors, and possibly remove componentry like high-mount centerstands.  Sometimes directions can be less than explanatory, and light fabrication work can be required.
  • Finally, parts often need to be reused - brackets, side stand bumpers, flanges, and clamps are often pieces that need to be pressed into service once again.  If yours are missing or damaged, you may need to obtain them from your dealer prior to your exhaust installation.

Hopefully, the mystery of aftermarket exhaust is a little less “baffling” now.  (Ha, get it?  Baffles?  I’ll be here all week.)  If you enjoy a little bit of wrench twisting, some bark with your bite, and a little bit of ‘get-up-and go’, a new exhaust might be the hot ticket for falling in love with your bike all over again!  If you’ve got any concerns, questions, or just thoughts for us - we love calls, and we’d love to talk about hot-rodding your bike.

-- Uncle Loomis

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