Welcome to My Exhaust Upgrade Page

This page will show you what I had to do to upgrade the exhaust on my SYM HD200. It is a MRP free-flow exhaust designed for the HD200 as a direct fit and is designated as usage for a type-2 GY6 motor of 170cc's. This is a direct fit replacement for a normal air cooled GY6 motor and should be as easy as a 15 minute bolt on job, but like everything else on this scooter, there were a few problems. Here I'll show you what I had to do to modify this to fir on the water-cooled SYM HD200 scooter even though it is designed particularly for the HD200.


Click on any of the below pictures for a larger one


This is the MRP and what came with the kit. Included is the muffler, the exhaust pipe, two straps, the mounting bracket and the screws to hold the mounts onto the muffler itself. It did not come with a exhaust pipe to muffler clamp or a new exhaust manifold gasket. You would figure that paying over $400.00 for it, they would give you the extra needed hardware---Nope. It weighs in at only a few pounds compared to the over 12 pounds that the OEM muffler/cat weighed. The pipe diameter is a bit bigger than the OEM assembly too so none of the original clamps would work and I had to use the original bolts too.




Here's a picture of the muffler mounted with only one strap being used. As you can see in this and the next few photos, I had to install the mount backwards. The mount is supposed to work with the two holes on the bracket going to the straps and not the swing arm as I did. It just didn't look right and it actually wouldn't fit right either so I had no choice.


By mounting it this way only one strap was used and I didn't like it. Although it was mounted on tightly, I wanted to figure out a way to utilize the second one and found a way.




Here's a close up of the bracket mounted upside down and backwards.


Since the original muffler has three welded on mounts on it, I decided to utilize the third hole for the second strap. The chrome spacer is a 7/16" deep socket for a 3/8" ratchet. I cut it to the size I needed and bought a  coated long bolt. I then sealed the inside of the socket with axle grease to prevent water from collecting inside. This mount isn't insulated with the rubber bushings that the main mount have but it's not really needed anyway.




Here's a picture of the second strap and the spacer/mount completed. I did it only for aesthetics originally, but later found out that I actually need it. The muffler is on very strong with the one strap and even stronger now with both.



Another view complete and ready to run




Less than 10 miles later the pipe has already "tempered."  I did adjust the A/F screw to richen it up before I added the new carb. The discoloration hasn't gotten worse and it doesn't clean up too well.


BIG PROBLEM!!!! The pipe touches the water pump--BIG problem. If this were a GY6 motor then it wouldn't be touching because it wouldn't be there. This means that I have to bend the pipe and fabricate a spacer.



Problem solved. I made a " steel spacer for the pipe. Sure it may look goofy and crooked, but there's a few reasons First off, I don't have access to a torch, bench drill or other machining tools other than air powered to "perfectify" it.  Second is that the SYM exhaust pipe mount is slightly crooked to begin with. Third is that it's the biggest piece I could get for free. Fourth is that " steel isn't exactly easy to work with on a small piece. And last is that it is mounted exactly in the orientation that you see above, "crooked" and all.

The only thing that matters to me is that all the holes line up and everything seals nicely. Speaking of seals, not shown are basic GM EGR bi-metal gaskets, one on each side of the spacer.




You had better think twice before trying to use this again. This is the exhaust gasket and is a clock spring design. Once you break the seal, it's done and you have to replace it with a new one. I didn't need a new one for the upgrade, but be warned if you have to take off your exhaust, you better have a new one handy.



This is the OEM exhaust and it goes into the block with the gasket outside and seated into a recess. The new pipe is a flush mount of a larger diameter and it effectively covers the recesses perfectly. Along with the gaskets and spacer, it is nicely sealed.

In summary it was a pain in the arse. Even though this was the first upgrade I did and didn't have a freakin' clue at the difficulties I was getting into for the future ones, it's been very "enlightening." cough cough :) Power was gained for sure and no less than 10 pounds in differences were shaved off. Below are some sound clips that I did with before, during and after the swap. I'll be adding a clip with the current free flow filter soon.

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Webmaster and Designer Jeff Byrd
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Revised: July 06, 2010