Tommarow, I'm going to try to derestrict the silencer, and internally polish the stock headpipe. With the silencer, I don't just mean taking the endcap off, I'm going to mess with the internals of the silencer. I'll report the results I get, if any.

 

its going to sound terrible unless you do something pretty amazing. I would change the baffle on the end of the pipe that the S/A bolts to. i think that is what makes the weird sound.

 

my friend cut the spark arrestor out of the endcap and put the endcap back on. it sounds a lot better than most aftermarket exausts. but its loud!!!!! it definately sound better than the yoshimura.

 

My plans are to keep the endcap S/A unit in tact, but actually try to improve flow by modifiying the internal baffle.

 

Update!: We (My dad and I) just finished polishing the headpipe on, and are currently working on the silencer. Things are looking good...

 

Don't bother with the endcap, all you'll do is end up with more noise.

There are more significant restrictions within the silencer itself.

There are 3 chambers. Exhaust travels into the center one first, then makes a 180 deg turn and flows into the forward most chamber. Then it makes another 180 degree turn and travels thru a pipe to the rear chamber, where it finally exits.

I have some pics & diagrams on my website. After you check out the pics, then click on the illustrations link for a detailed diagram of exhaust flow and what I did on mine.

By freeing up these restrictions you will gain a good amount of bottom end throttle response as well as some mid. It won't sound noticibly louder than stock if you do it correctly. It's a great sleeper mod and yeilds good gains for no money spent & without the noise of an aftermarket pipe.

e-mail me if you have any further questions....

 

The pipe is finished, and the results are in!

First, we took off the entire exhaust system and examined what could be done to the headpipe. The two pipes where the header meets the engine had a lip inside, with some rough welds, so we took out a die-grinder and ground the lip down, then we polished up the surface with the dremel.

Then we moved on the the silencer. Upon removal of the endcap, you could see where the major restriction, a large baffle plate with a tube of about 1 inch diameter going through it. To eliminate this restriction, we drilled out 7 3/8 inch circles in a circular pattern, then a 3/5 inch hole in the center of the baffle plate.

After putting the endcap back on, and getting the pipe reinstalled with new copper crush gaskets, we fired it up. Off Idle, it was a bit louder, but not too much louder. The tone sure was different though (sounded much like the supertrapp I used to have on my highly modded xr185). Running through the rev range, the volume wasn't much louder than stock, but had a much throatier sound to it.

Now to see if it was anybetter in a performance aspect! The first thing I noticed was it felt to have a boost in low-mid range power. Upon my accelaration test down the road, I noticed that it reved out quicker, and that I could shift through the gears much quicker than previously possible.

This mod was well worth the time my dad and I put into it, and in my opinion is a good, cheap mod. I will try to get some pics of my setup soon, so It's easier to understand what I'm saying.

 

Also, I would like to thank 86atc250r for his knowledge on how to complete this project. I think that I will buy a uni filter (I've had a bad experience with K&N) and play with the jetting to see what kind of gains find, and report what, if any, I get.

 

I did basicly the same mod. I drilled three 3/4" holes in the plate where the 1" stock hole comes out. I think I may drill more, and grind the stock edges of the headpipe. I also noticed a bit more low-mid power, and could pop wheelies easier. Sounds good too. quiet, yet a little sharper, and "snappier". I plan on getting a stock pipe and doing internal mods. does anyone know if bronzing works to weld it back together? I also have access to an electric welder.

 

drilling holes are good.... but the major restriction IS the endcap...

the quiet-core (pipe with holes) that is inserted into the endcap, and of which the spark-arrestor is connected to; is the smallest pipe size diameter in the entire exhaust system...

just take a hacksaw and cut off the quiet-core / spark-arrestor combo from the endcap...
make sure to take a pair of channel-lock pliars and bend the remaining lip out as much as you can for greater exhaust flow thru the endcap, and put it back on.....

then you can go ahead and drill out the first baffle if you want....

I'd even get a super long drill bit that reaches thru to the font baffle also