MZ/MuZ Riders

I know there's a huge group of you 1000S/SF/ST owners here that have been wondering if there's anything to gain by removing the catalysts from the pipes. I too have been thinking about removing them myself, but figured that the bike ran fine with them in, and worried about loosing bottom end torque, at the least, so decided against it. Seeing how I've had the bike for 6 years, the mileage is up there, and I've run out of things to do to it to increase power, besides gutting things or head/engine work, and that I wanted to increase the exhaust note somewhat, I did as much research on other forums to see what others have found on some other bikes. Nothing out there about these bikes obviously, but the majority of people stated that they felt some power increases, as well as a slightly louder exhaust. I'm running Sebring Twisters (with the baffles in for now, more on that later) There are some who say you would lose low end torque due to the lack of the back pressure if the catalysts were removed, with out rejetting/mapping, but I imagine with remapping that would possibly be offset?? All seat of the pants for now, and maybe some wishful thinking?

Anyhow, saturday I spent removing the headpipes, and used a 1/4" X 12" long drill bit and a 3/4" flat wood boring type drill bit with an extension. I first drilled a bunch of holes with the 1/4" bit, then followed with the flat wood bit and drilled the center of the catalysts and then used a long handled flat screwdriver to chisel/chop/pry/scrape the rest of it out of the cores. It actually went pretty easy. The wood drill bit actually grabbed hold of the corrugated core and quickly twisted it up and ripped right through, and broke apart into chunks and I was able to shake it out. Then I used the long screwdriver to chop out the rest that was still attatched to the inside of the pipe walls. Again, it was'nt as time consuming and difficult as I thought it would be, the left pipe is a piece of cake as the core is close to the end of the pipe, the right side was the one I figured would be a chore due to the length and angle of the pipe past the core. Not so, the drill bit ripped it up and apart quickly.

Took it out for a good ride today, and the engine seems to pull stronger than before from 5000rpm up where as before it was around 6000rpm and up. Did'nt notice any decrease on the low end, or up top. No popping on deceleration, no flat spots or surging etc. The biggest thing I've noticed is that there is a very noticable change in the speed in which the engine revs out. It revs noticably quicker, without a doubt. (43,000+ miles of ownership...one knows when theres a change!!)

I'm running a Power Commander (with the factory upgrade map) with my custom K&N air filter with modified airbox, with the Sebrings w/baffles in. I'll be taking apart the silencers so I can remove the discs welded inside the core (the baffles are centered within these discs, and when you run without the baffles, the exhaust flows through the small hole in the disc....and it affects the sound, kind of a hollow poofy slightly puffy sound at idle and lower rpm's that I don't care for. I want to run them truely open like other aftermarket silencers, and put the bike on a dyno and get the mapping spot on for everything. As soon as I pull the head and do som pocket porting, and serious work on the short side radius, then it's off to the DucShop in Atlanta, GA for mapping.

Glad I finally yanked them things out!

Lorin
Did you read my post on the subject?
George

George, I know I read about it here a few years back, did'nt you cut the things off and have sections re-welded in or something? I must have not looked back through the previous posts very well

Lorin
Yes I did cut them off and remove the innards (as you did) and I re-welded the cat cans back in. My reasons for doing so were more concerned with safety rather than performance as I have always considered cats as a "shut the barn door after the horse has bolted" type remedy for a poorly designed engine, apart from which I do not consider a white hot cat can under the engine to be a good idea!!. With hindsight I should have replaced the cans with a straight section of pipe as the empty cans are now acting as a (Kaden type) resonance chamber and affecting the fuelling slightly causing the exhaust to "over scavenge", in effect drawing some of the incoming fuel charge out with the waste gasess. This was suspected when my wife riding behind me on her duke complained of a faint smell of Gasoline/petrol, and when I hooked the bike up to a friend's gas analyser it was confirmed. Physically the only effects that I have noted are an increase in engine flexibility, the engine seems to rev-out at an increased rate and the fuel consumption has gone up a little. When I get time I will see if I can re-map using the Tuneboy sofwear that I have. As you are going to re-map your engine anyway it should be easy to compensate for this problem at the same time. As to modifying the porting on your engine this may be difficult because from what I have seen of the head internals this would appear to be a "de-tuned" racing engine rather than a tuned production motor. I had the same feeling a few years ago when looking at a Yamaha TRX motor (the dry sump was the first indicator) my feelings were confirmed when I discovered that the engine was derived from the purpose built XTZ Paris-Dakar motor. (I now own one).
Good luck with any of your modifications.
George

George, It will be interesting to see what effect it has on mpg, I"m averaging between 41-46mpg with al that I've done. As far as porting, I'm talking more smoothing of all sharp edges, smoothing the short side radiuses, and bowl work just below the valve seat and possible unshrouding of the valves. Definately no enlarging of the runners, as then we get into velocity issues. Looking for smooth unobstructed flow. I had the head off of my Benelli TNT last year to fix a leaking valve guide, and did all the above. The bowls were rough finished, they were choked just below the valve seats last angle cut. I was quite surprised that they were as bad as they were, rough and sharp edges, very abrupt and sharp edged short side radiuses ,not a trace of cleaning up of anything. But something tells me I won't find the same with the MZ......

This is on the to do list when winter arrives...Thanks for the input from you guys that already did this and a little inspiration from posts like this one.They refer to the Aprilia Dorsoduro 1200 as a major choke point.It has great pictures too.

http://www.apriliaforum.com/forums/show ... 299&page=4


" I love the air chisel for gutting cats, nothing has quite the destructive force of a proper air-hammer with nice new/sharp cutting bits! To do the final clean up on the inside of the pipes I used a die grinder and a combination of fine stone and flap wheel, as you can see not quite all the junk came off the inner walls of the pipes but at least 99.9% did!

As soon as this bike comes back in for the 600 mile service we shall see on the dyno exactly what the difference is between catalyzed pipes and non catalyzed Arrow link pipes!"