Welcome to the fourth in our series of customising stories. The idea here is to give you some ideas, demystify the whole customising thing and provide a few useful contacts. Please let us know what subjects you’d like us to tackle — we’re here for you.
The art of sound
There’s a little more to those shiny tubes than meets the eye — or ear
Your bike’s exhaust system performs a number of vital functions: it vents combustion waste products from the engine, helps to draw fresh mixture into the combustion chamber and acts as a muffler to reduce the noise of combustion to a sociable level.
When correctly designed and tuned, it can improve power delivery and have a beneficial effect on fuel consumption. All that and it must look good, sound sweet and weigh as little as possible.
OK, let’s have a look inside: spent gases are pushed out of the combustion chamber into the header pipe by the piston rising on its exhaust stroke. The waste gases are travelling at a brisk clip and, the smaller the diameter of the exhaust pipe, the more quickly they can move, promoting efficient scavenging of the cylinder and so minimising exhaust gas mixing with the incoming charge.
An efficient exhaust is a free-flowing exhaust. Restrictions can increase back pressure, or contamination of the fresh mixture in the chamber. An increase in pipe diameter beyond the calculated optimum can do the same thing — should the pipe widen in diameter, the pressure of the expelled gases drops, speed falls and, believe it or not, the gases can begin to flow back up the pipe. Running at low engine speeds or on a trailing throttle can have the same effect.
The exhaust gas is accompanied by a much faster travelling pressure — sound — wave. This, you’ll be astonished to learn, travels at the speed of sound (plus a bit for boosted temperature and pressure). When that wave passes through an opening, such as the end of the pipe, a reflection, or negative pressure wave is created that runs back up the pipe to the combustion chamber, drawing out residual exhaust gases and reducing pressure in the chamber, which accelerates the incoming charge.
Tuning these pressure waves by varying the length of the pipe can benefit power generation and fuel consumption; and the pressure wave itself is a major contributor to the exhaust note.
And so to the muffler. In motorcycles, these come in two basic types: most common in performance mufflers is the straight-through perforated bore with an absorbent wrap (typically glass fibre wool) around the internal circumference for part or all of its length.
A more complex design channels the exhaust gases through smaller sub pipes and sharp bends within the muffler, slowing gas flow and reducing noise.
And speaking of noise (rather than music), our motorcycles must comply with all relevant Australian Design Rules (ADR). The rule concerning exhausts, ADR 39a, requires that any bike built after February 1985 generates a maximum of 94dB(A) in a stationary test and its exhaust system must bear a clearly visible stamp showing its noise test results.
Restrictions or not, it all adds up to some sharp design and manufacture and perhaps explains why we don’t see too many bikes fitted with lengths of 50mm-diameter guttering downpipe in place of the factory exhaust. There’s no need. There are plenty of custom exhaust manufacturers out there that know their business. Such as these good folk…
There’s no bigger name in motorcycle exhaust design than Vance & Hines. This American outfit has been designing systems for cruisers and superbikes alike for decades. When we alerted the California crew that we were about to run a piece on custom exhausts, they pointed us to their new system for the sexy XR1200R Harley Sportster. It’s a classic example of modern exhaust design and manufacture. It’s a 2–1–2 unit they call the Widow, is finished in a smart black with high-level dual mufflers and strengthens a good, even power curve, according to the V&H website (vanceandhines.com). It provides a peak of 85bhp, up by a useful 5bhp from standard at the peak, with solid gains right across the rev range. And, given our newfound wisdom on the subject of exhaust design, we’ll all no doubt be gratified to learn that the Widow comes with “twin high-flow mufflers” and “performance-tuned headers”.
While we’re talking H-D, it will no doubt surprise you not at all to learn that there’s a mad mile of aftermarket exhausts for Milwaukee’s meatiest. Kerker, Hooker, Arlen Ness and Paul Yaffe, to name but a few of the better known, all offer custom H-D exhaust hardware — as does Harley-Davidson itself under its Screamin’ Eagle banner. But as the range is for “racing only”, Harley Australia declined to provide us with any info on their wares.
Harley-Davidson pipes come with their own argot as well: there are shotguns, slash-cuts, fishtails, duals and drag pipes. Most of these are different muffler designs and each will give your bike a different look and sound; and many will have an effect, usually modest, on its power delivery. Drag pipes are different: they’re straight-through pipes that’ll bring down the walls of Jericho and your licence with them if you use ’em on the street.
A relatively new feature of the humble exhaust system is the end cap and, typically, these very fetching adornments are becoming a major feature of aftermarket exhausts across the Pacific on, you guessed it, Harley-Davidsons.
A big vote of thanks to Brenton at Show and Go Motorcycles (showandgo.com.au) in South Australia for sending us a couple of discs laden with images of current exhaust technology, so giving us a peek at Paul Yaffe’s Afterburner and Holy Moly end caps.
Typically, the range of stuff available for metric cruisers lags a bit compared with the range of goodies available for American metal, though that’s changing, slowly.
Supertrapp — also available via Show and Go — makes systems for Honda, Kawasaki and Yamaha cruisers, some with their diffuser disc end-cap system, which allows the user to adjust the sound and power output by adding or removing discs fitted to the end of the muffler.
Vance & Hines offers a full range of systems for metric cruisers, including the Suzuki M109R and Honda VTX1800, but V&H itself, in the person of the ever-helpful Shannon Dwyer, suggested we take a squiz at the firm’s new Big Radius 2–2 system for the Yamaha V-Star 950, a twin-pipe system with slash-cut mufflers that’s made to be big on mid-range power and low on noise. Check it out online — either at Vance & Hines or through their Aussie distributor, Cassons (cassons.com.au).
We didn’t have too much success coaxing information from Australian manufacturers when preparing this yarn, but we know Bikecraft (Bikecraft.net.au) is taking some experimental steps in cruiser exhaust manufacture after putting together some tough-looking units for big-bore sports/tourers such as the Suzuki Hayabusa and Kawasaki ZX-14, and Dennis Foran continues a flourishing line in custom exhausts from his hideaway on the Central Coast of New South Wales. If you’re looking for something special, chances are Dennis has already come across it and probably made it in his 30+ years of toil in the business. You can find him, and images of his bespoke pipe service, at foranexhausts.com.au.
Thankfully, lots of the cowboys that plagued the industry in decades past seem to have disappeared and most suppliers that remain are knowledgeable and ready to listen to their customers. But danger still lurks. Because they’re often quite straightforward to fit, many riders — including yours truly, I’m ashamed to admit — would rather buy a system over the internet than have to undergo the annoyance of talking to another human being to explain what they want.
Don’t do it. Consult the experts before you hand over your hard-earned. Many moons ago, I bought a system for the four-cylinder sports bike I was riding at the time and discovered to my dismay that my snappy-looking new system not only robbed the bike of its already marginal mid-range power but made it run dangerously lean and reduced cornering clearance so much it was quicker to get off and push the bike around right-handers. Ain’t no sense in learning the hard way if you don’t have to.
We’ve come a long way in terms of materials, too. The widespread use of stainless steel has seen flimsy, Christmas cracker chrome banished to where it belongs — on the oversized wheels of custom cars that only come out on sunny days. Because the cruiser crowd lack the obsession with weight so prevalent among sports bikers, we’re not usually offered the titanium or carbon-fibre you’re apt to find on pocket rockets, but no matter. Steel is strong and durable. Bit like us, really.
Custom exhausts don’t come cheap. You’ll be paying a minimum of $600 for a slip-on muffler and way better than a grand for a full system. But for that you get a product tailor-made for your model that makes the best of its available power, often makes it run a little more frugally and looks damned good into the bargain. There are riders, too, who will tell you with good reason that an aftermarket exhaust can help advertise your presence on the road to inattentive car drivers. But, me, I like ’em because I can hear not only what the engine’s doing but whether it’s happy or not, and that’s as good a reason as I’ll ever need for a free-flowing pipe.
Staintune — 51 Cavendish St Mittagong NSW 2575 Ph 02 4871 3188, www.staintune.com.au
MC Performance — 16 Victory Court Trafalgar Vic 3824 Ph 0418 549 730, www.mcperformance.com.au
Foran Exhausts — 3/14 Luke Close West Gosford NSW 2250 Ph 02 4325 0614, www.foranexhausts.com.au
Thunderbike Powersports — 29 Bolt Rd Tahunanui NZ Ph 64 3548 5787, www.thunderbike.co.nz
Formula 1 Motorcycle Exhausts — 75 Ebsworth St Tamworth NSW Ph 02 6762 8077, www.formula1mc.com.au
Pro Ex — 99–111 Monash Drive Dandenong Vic 3175 Ph 03 9756 3700, www.proex.com.au