Bulldog exhaust mod
submitted by Walt, ZRXOA #255.
The "Bulldog" muffler is a modified stock muffler with all baffles removed except for the flat plate diffuser. Also the "can" length is
shortened 7.5" and it's polished to a mirror finish.
- I removed the muffler from the bike, drilled out 3 pop rivets holding the end cap & removed it.
- Remove baffle assembly. Instead of removing all the baffles, retain the first one. Simply cut the baffle assembly into with a
hacksaw just downstream of the 1st baffle (the perforated plate). This is 12" from the exhaust end shoulder.
- To shorten the muffler, measure and make a circumferential mark 7.5" (or whatever seems right to you) from the outlet end of the
muffler can with a lead pencil. Put 2 wraps of duct tape adjacent to the marks on the inlet side to prevent damage to the finish of the
can. TAKE YOUR TIME and CAREFULLY start a cut using a hacksaw all the way around the can on the mark you've made. Complete cutting off
the 7.5". Dress up the raw edge of the cut using a file and sandpaper or whatever you have handy.
- Secure the fiberglass blanket material to keep it from blowing out using one wrap of stainless steel wire at the area of the plate.
- Put the modified baffle assembly back into the outer muffler sleeve, replace the end cap using high temp silicone to prevent leaks
and install new pop rivets. 5 lbs of weight is eliminated.
Since making the above mods I've cut off the header pipe within 1/4" of the gasket flange (See pic below), based on a trick Dale Walker
does on his Vortex slip, which is claimed to be worth 1.5 additional HP. You can run the Bulldog without re-jetting. It runs fine with a
noticeable improvement in throttle response and performance. The sound is like a Kerker slip/bolt on. The neat thing about the Bulldog
Muffler mod is it costs nothing, is simple and low tech (most of the work is done with a hacksaw), and you can try out the muffler
without the baffles before you shorten the can. If you don't like the sound, you can put the baffles back together with a couple of spot
welds. I've also polished up the "Bulldog" to a mirror finish and it looks pretty darn good. Polishing was accomplished by removing the
hard plating CAREFULLY so as not to gouge the soft aluminum, using a fine wire wheel on an electric drill. Then it was sanded using #400
wet & dry, and final polished using "Semichrome" and a lambs wool buffing pad on the drill. This little job will take about 4 to 8
hours. I spread it over several days, as it's boring!
Hotdog, Son of Bulldog exhaust mod: HOTDOG - The new "Stage IV Hotdog" muffler mod is an evolution of the
Bulldog. It is quieter and has less backpressure. Essentially the mod converts the Bulldog, which is a shortened and gutted stock
muffler with only a plate baffle, to a 2 ½" straight through glass packed muffler, similar in design to many commercial slip-ons, with
the exception that the dimensions are optimized to offer minimum backpressure based on the stock header size for maximum HP. Reading the
Hotdog mod procedure, references to the Bulldog mod, above, may be necessary.
- Start with a shortened Bulldog muffler (dimensions are based on the can having been shortened 7 1/2"). Drill out the 3 pop rivets
and remove the end cap.
- Remove whatever baffles you're running from the can and cut off the lower 1" of the baffle assembly holding the 3 mounting bolts. I
used a "whiz wheel", but a hacksaw works fine. To remove the baffles, use a rubber hammer or 2 x 4 and tap the 3 protruding studs to get
things moving, then tap out the rest of the way using a hammer handle or 2 x 2.
- Order a ring of aluminum, 2 5/8" O.D. x 2 ½" I.D. x 1 1/2" long. Align it perpendicular to the inside of the end cap and tig weld
it. I had this done by the friend-of-a-friend for $20. One six-pack may work for you!
- Order a piece of perforated muffler tubing 2 5/8" I.D. x 11 ¼" long and slip it over the aluminum ring.
- Wrap the tube with enough muffler packing (from Aircone) to fit a 51/2" I.D. can and the tube length. Taper the packing with
scissors as required to roughly match the taper of the inside of the can at the header end.
- Put the mounting flange with the 3 bolts into the muffler can and mount the can on the bike. Install the new baffle assembly and end
cap. Pop rivet the end cap in place, and you're done.
Notes for the Hotdog
- Aircone (In the U.S.) supplied the parts for my mod. Cost was $22 and change, including shipping. Contact Gary Williams at
702-566-1077. Tell him Walt C. sent you.
- Note: My header is cut off within ¼" of the flange. If you choose not to cut your header pipe, the perforated tube SHOULD slip over
the outside of it. I think 2 5/8" I.D. will work, but measure just to be sure, as mine is gone!
- OPTIONS - Several options are possible, listed from quietest to loudest.
Stage I - (Stock length and stock header) Offers stock look, quieter - Just order an 18 ¾" long perforated tube and more packing.
Estimate this would add $13 to your bill of materials.
Stage II - (Stock length and shortened header) Offers stock look, quiet and minimum backpressure - Just order an 18 ¾" long perforated
tube and more packing.
Stage III - (Shortened length and stock header) - Better looking than stock, fairly quiet.
Stage IV - Walt's "HOTDOG" (Shortened length and shortened header) Better looks than stock, acceptably quiet, minimum backpressure,
maximum horsepower. "Serious hardware for the aggressive rider." How's that for a sales pitch?
- If you don't get a jet kit, you'll probably want to raise the needles with a couple shims. I make no claims that Hotdog will work
properly without re-jetting.
- QUIETER VARIATIONS - Further variations are possible using smaller diameter perforated tubes, to reduce noise at the expense of
increased backpressure. Re-jetting may not be required. The downside is that adapters would be needed going from header to perf tube and
outlet to perf tube, driving up the cost of the mod by an estimate $14.
- MAINTENANCE - Glass packed mufflers get louder over time as the fiberglass packing gets blown out. When this happens, just order
some more from Aircone.
- This information is offered as "shareware" to those who don't mind trading some sweat for $$$, or just like to tinker. Some may
think this is too difficult. Just my opinion, but a trained monkey could do it! Be aware your warranty will probably go into the toilet
with this mod and you'll be illegal in some states, due to E.P.A. regulations and noise ordinances.