Custom, Tunable Supertrapp Slip-ons

Editor's Note: This exhaust system involves a little more DIY work than simply buying a Muzzy and taking it out of the box, but our author thinks it is worth it. It's not really that much extra work, and you end up with something that provides a greater amount of flexibility than most of the currently available systems.

Supplies

• Two Supertrapp universal application race cannisters with discs and caps, with 1.5" ID inlet. They come with t-bolt clamps, 8 discs, end caps, and weld-on hangers (not used in this application). They are about $150.00 each at MAW Online. Can probably be found used.

• A set of "donor" stock cans, preferably painted (non-chromed), as you have to weld extensions onto your midpipes. You are interested in the midpipes, which you will cut off the cans. Stock cans are usually available on eBay.

• Enough straight pipe to extend the donor midpipes rearward by 6"; give yourself a buffer. A local Midas shop did this one for $20, parts & labor. He used pipe that was the same diameter as the midpipes and expanded it slightly where it overlaps the mids for consistent pipe diameter back to the mufflers. He then welded the new material onto the donor mids.

• Two 3.9" diameter stainless steel t-bolt clamps from Summit Racing. Our fabricator couldn't remember the exact ones he used, but they should be something like this. About $11.00. Rubber insulators, from a set of muffler straps that were too large, were used under these.

• Two rubber exhaust hangers from Pep Boys, about $4.00 each. They are oblong and have holes 2" center to center. You'll use these to mount the Supertrapps to your existing rear peg brackets. The bottom third of the hanger will need to be narrowed by 1/8" (on the inside) to accommodate the bolt in the t-bolt strap and two washers; this is easily done with a small hacksaw and file.

• Two stainless bolts/nuts just like your stock cannister hanger bolts, but 2" in length to accommodate the new rubber hangers. You'll also need two appropriate fender washers for the back side of the rubber hangers.

NOTE: The biggest - and really only - headache that came while building this system was the infuriating paucity of aftermarket cannister straps that are less than 5" across. Not everyone has cannisters the size of trash bins. But the t-bolt straps are attractive and work well.

Process

Begin by cutting the midpipes off your donor cans. Make sure you cut them all the way back to - but not including - the weld. Clean up the edges.

NOTE: If you hold the cut mids next to one another the way they'd be on the bike, you'll note that the clutch-side one has a very slight "leftward" angle at the rear edge that's about 1/4" inch long. KEEP IT. Your factory left muffler has a built-in accommodation (at the conical entry) for the final drive and left swingarm that is barely perceptible in your bike's stock symmetry. But with shorter cans that do not have this built-in accommodation in the left side, it will be.

What you're going to eventually do is swap the mids, left for right, when mounting; doing so will allow you to establish a very near-symmetrical aesthetic balance in your new system, as well as accommodate your sidestand and centerstand, just like stock. Try that with a Muzzy or Yosh! Two Brothers Racing does have an accommodation for your centerstand. But you're not building it yourself.

Go to your friendly local welder or exhaust specialist and ask him or her to add 6" to the rear of each of your mids. Ask your welder to use the same diameter pipe and to heat/mechanically expand it to fit over the cut midpipe before welding. This way, your newly extended mid will fit inside your Supertrapp inlet without issue.

Paint your completed mids and stock clamps with exhaust paint. You could powder coat them, but it's pricier. Another alternative is to use exhaust wrap on your mids, which has aesthetic and scientific merit, some believe. Others believe it merely makes everything rust quicker.

NOTE: You may want to mock up your system on the bike now, before you paint.

Now you're going to do your assembly, assuming that you have unbolted your stock system. Remember to swap your midpipes left for right, and install your mids onto the headers with the clamps over the leading edge of the mids. Swapping the mids will allow you to bring both cans into close symmetry. They should fit snugly. Do not tighten.

Carefully measure the length of your Supertrapp inlets; you should have about two inches of overlap on the rearward end of the mids. Mark your "depth" with masking tape; you don't want to slide the cans up too far and then have to pull them back, marking your paint.

Place the small t-bolt clamps on the cans' inlets, then slide the cans onto the mids up to the tape. It's better to mock up both sides and check for symmetry and clearance from adjacent surfaces like the stands and swingarms before tightening any clamps.

Take your rubber hangers and, if they are the 1" thick kind used here, use a small hack/holesaw to make a 1/8" cut ACROSS the hanger (perpendicular to its length) one third up from one end. Then cut up from the bottom so you remove a 1/8" "slab" of material. Clean up your surfaces with a file. You are doing this so that your t-bolts, washers, and nuts will fit through/on the hangers with thread to spare.

Place your large t-bolt clamps and rubber insulators on your Supertrapps, with the threaded end of the bolts facing the bike. Mount the tops of the rubber hangers to the INSIDE of the rear footpeg brackets. You may need bolts longer than 2" if you want to keep your rear pegs. The bolts will be tight going through the rubber mounts. Thread them through with a socket wrench. Secure them loosely with a flat washer and nut.

Place small flat washers on the bolts of your t-bolt clamps, pass the bolts through the lower hole of the rubber mounts, place another flat washer on the inside of each mount, and loosely secure the supplied locknuts.

Now is the time to snug up all joints just enough so that you can align everything for symmetry and clearance. Check to see that your stands and swingarms are not contacting the exhaust, except where the stop on your centerstand rests on your left can inlet. Also, check to see that your cans are rotated so that the logos are laterally level, as seen from the rear of the bike. When you are pleased, snug everything up. DO NOT OVERTIGHTEN FASTENERS. Put little rubber vacuum hose caps on the exposed threads of your clamps at the muffler inlets; it's clean and neat.

At this juncture, you may install your discs. The minimum recommended number for each can is four. On a stock motor, five discs seem to work to good effect upon dialing the system in. If you have re-jetted, you may need more or less. Install the end caps. Use the supplied anti-seize on each bolt before final installation.

When you are pleased, fire up the bike as you normally would. In addition to the improved (and louder, but not obnoxiously so) tone, you will likely notice a perceptible improvement in off-idle throttle response, as well as an improvement to throttle input up on the cam. The motor seems to pull more, with less apparent restriction. Your motor may also run a few degrees cooler because the stainless steel 'trapps have a larger diameter, are shorter, and may dissipate heat more effectively than longer, chromed or painted stock cans. Many favor stock exhaust (and that's fine), citing the math and physics behind it, but this motor seems very pleased about this whole notion of tunable, usable, performance-oriented exhaust.

After you have logged 100 miles or so, check your fittings.

The sound is a lot like the Two Brothers system, except it's a "rounder" sound with no "sharp edges", so to speak.

Sound clip

Hopefully, this will provide a viable option for aftermarket performance exhaust for the EX250. By being tunable (by adding or removing discs) this exhaust provides adjustability that other aftermarket systems lack.

Owner reaction

After several rides: With five discs in each can, a properly tuned stock motor idles steadily at about 1300 rpm, has crisp throttle response off idle, and no flat spots. This seems to be a very happy bike.

Thanks to the hard rubber mounting fixtures to the rear peg brackets, there is virtually no vibration, and the stainless cans dissipate heat very effectively. Moreover, though the bike is louder than stock, it's not annoyingly so - one could still easily have an Ipod bud in one ear - and there are no unpleasant or jarring tones at any rpm. The bike's sound is reminiscent of a 90-degree V-twin... like a small-displacement Ducati Monster.