Motorcycle Exhaust-System Comparison: Pipes for Kawasaki Big Twins

Almost one fourth of the people who responded to the reader survey in our first issue said they planned to buy an exhaust system for their bike in the next year. If you apply this percentage across the entire cruiser market, you begin to understand how a representative of an aftermarket company that makes top-quality accessories for cruisers could say that, even with all their billet products, the single largest portion of their business still comes from pipes.

Being curious folks, we decided to see what pipes were available for our long-term Vulcan 1500 Classic at the tail end of The Year of the Cruiser. The results of our initial query of pipe manufacturers illustrated two facts we were already aware of. First, with six manufacturers sending us pipes for a bike that has been on the market for less than a year, we can confidently say that there are more exhaust customizing options than ever available in the Japanese cruiser market. Second, since half of the pipes we tested were either pre-production or first-run production items, things weren't always so rosy in this segment of the market. These thoughts lead us to wonder how these pipes would compare to each other, how well thought-out they were, and if they would fulfill the conflicting demands of good power and good citizenship.

White Brothers of Yorba Linda, California, which sells some of these brands of pipes itself, was kind enough to provide its DynoJet dynamometer for the horsepower numbers and R&D Mechanic Dennis Emerson for the wrenching and installation advice and expert commentary. We timed each installation and rated it on a scale of one to five, with five being a perfect score. Next, we ran the bike on the dyno to figure the vital stats. All the pipe manufacturers, with the exception of Cobra, which sells its own jet kit, recommended using a DynoJet jet kit with their pipes. We tested each pipes with the jet kit requested.

Sound levels were tested at the AMA standard of 20 inches at 45-degree angle from the pipe opening with the sound meter facing away from the pipe and the engine at a constant 3000 rpm. The drive-by sound test was taken at a distance of 12 feet with the Classic driving by at a constant 45 mph in second gear, which translates to about 3000 rpm in the real world. Decibels are calculated on a logarithmic scale which means that if a sound increases by 10 decibels, it's three times as loud. An increase of 20 decibels translates to almost 10 times louder. Since our sister publications Motorcyclist and Sport Rider established 104 decibels as their maximum acceptable sound level for street use, we decided to maintain the same limit for our test. Though it's a bit arbitrary, going above guarantees that you are making enemies for motorcycling every time you ride your bike.

How did the pipes perform? All of the pipes weighed in less than the stocker -- some by as much as 20 pounds. All made more power. All were louder than stock, but some were unacceptably so. Most of the headers blued, a problem caused at least partially by running the bike at full throttle on the dyno immediately after installing the pipes. While several of the pipes' heat shields did a good job of hiding the blue, taking new pipes through a couple short, reduced-heat cycles before getting them thoroughly warm may reduce bluing. Finally, some of the pipes limited ground clearance.

Note that just changing the jet kit improves power significantly. It also improves driveability somewhat, even on the 1500 Vulcan Classic, which is already very good in stock form. If the power increases these pipes offer aren't enough for you, Emerson suggests removing some of the intake plumbing and adding a K&N air filter.

Stock System
Staggered duals, $NA, 33.5 lb

Installation time/ease: 1 hour / 3 points
Peak horsepower: 48.1@4500 rpm
Peak torque (ft.-lb): 71.3@2500 rpm
Sound level at 20 in.: 92 db
Sound level rolling: 81db

The factory exhaust system has the unenviable job of meeting EPA requirements while providing an appealing exhaust note, appearance and performance. Only in the power department does Kawasaki's compromise make itself noticeable. However, the huge performance gains of yesteryear are no longer achieved by simply bolting on a pipe; OEM units are too well designed. Aftermarket pipes now offer more moderate gains, the opportunity to customize, and instant weight loss. At 33 pounds, 8 ounces, the stock pipe is a porker. Much of this comes from the expansion chamber under the swingarm.

To see how much power came from the pipes and not the jet kit, we ran the stock exhaust with both the stock and DynoJet jets. The DynoJet kit yielded 1.2 horsepower (49.3 peak) over stock jets, and improved throttle response as well.

One note about removal: If the system is hot (and who would remove a hot pipe but people who have six more to put on and test), you run the risk of shearing off the studs connecting the headers to the expansion chamber. The complexity also makes it a bear to put back on.

Cobra
Classic Slash-Cut, $380, 12.8 lb.

Installation time/ease: 50 min. / 3 points
Peak horsepower: 51.8@4500 rpm
Peak torque (ft.-lb): 72.8@3000 rpm
Sound level at 20 in.: 103 db
Sound level rolling: 90 db

Initially, we wondered why Cobra would sell the Classic slash-cut exhaust system with only three little heat shields, but Cobra has since expanded the pipe kit to include full-coverage heat shields, which were formerly sold as an option. The full shields protect the rider from heat and hide the top part of the header where chrome pipes are prone to bluing.

Installing the Cobra pipes took time because of tight clearance between the rear cylinder's canister and the rear axle. After trying several methods, we bent the pipe's bracket outward to gain more clearance. Cobra provides a bracket to move the voltage regulator (which hangs under the swingarm to hide the ugly expansion chamber on the stock pipe) to a less-visible location, cleaning up the left side.

The Cobra system ranked in the middle of all the categories we tested, providing a decent power increase without crossing over our maximum streetable loudness. Combined with a Cobra-assembled DynoJet kit, the Cobra pipes produced a maximum of 51.8 horsepower and 103 decibels. The only difference between the kits is Cobra's DJ132 main jet versus DynoJet's DJ136 main jet.