[UPDATE 9/25/15:]

Stock Z8 Muffler End Mod

Still baffled as to why the exhaust connections moved even though we now know some of the springs were not doing what they should have. I had it stuck in my mind that excessive pressures must be at play here. So, while it was still apart waiting on another part for another modification I decided to test the exhaust pressure at idle and at 6K just sitting in the shop thinking this would give me some idea what was going on. I removed the rear cylinder's O2 sensor and adapted in one of two low pressure gauges I have. Although this probably isn't the best way it did give me an idea of what was going on. I used both types of gauges and although the pressures were not steady by any means, it showed at idle at that location it averaged 1.5 lbs and at 6K it averaged 3.5 lbs. In my day we talked about ounces of back pressure not pounds so I did a little research. Seems it is not uncommon for V-twins to have pulses of pressures that exceed 2 lbs. But 3-4 lbs was generally viewed as unacceptable.
I then removed the muffler's end pipe and spark arrester and ran the tests again. This act cut the numbers in half. So there was still some restriction in the piping and through the muffler.  Because throttle response was quicker I decided to modify the end with a new design to remove that restriction.  I made a new one piece from 2" mandrel-bent pipe and some ¼" plate steel. 1/8" would have been fine but I just didn't have any on hand.
Had to make the flange first and with the aid of my drill press and a 3.5" and a 2" bi-metal hole saws and a template I made from the OE pipe, I make this flange.





I ordered the pipe from amazon already bent and cut off where I needed to:





Mounted the flange on the muffler and positioned the pipe so it would have a ½ bubble downward slope to keep water out and welded it together. I'll tell you why I didn't go more downward later:





Here you can see the pipe size difference between the stock 1.25"(about) and the new 2":



And here is a before photo of the stock pipe:



And after with the new unit:







And looking down on it:



If this works out, I'll sandwich a dish-style HMF spark arrester between two gaskets at the muffler. If not, no harm- I'll just put the stock end back on. The reason I wanted it simi-straight is because the plan is to buy this Benz silencer -

http://www.ebay.com/itm/BENZ-SILENT-RIDER-EXHAUST-SILENCER-JOHN-DEERE-GATOR-825i-2015/201513477422?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D36188%26meid%3D9d5f3080417b4df3ac2ae041b6b4bf4b%26pid%3D100011%26rk%3D1%26rkt%3D5%26mehot%3Dlo%26sd%3D191669904430

- that will slide on that pipe, clamp and hook on a bracket across the back to make the wife happy when she's along. Right now.. like this it's a hair louder..not much  but deeper then it was. A little meaner one might say. I'll do a sound clip soon. I have one more mod to do to the intake and I'll take her out for some tests. I'll post the results here.
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UPDATE 9/25/15:

OK, did a little sound clip. Just in and out of the shop a little. Need to get it out in the wide-open next.

https://www.youtube.com/watch?v=cJqv6LAnArI
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UPDATE 10/5/15:

Gasket came today so I decided to install the HMF Spark arrester. Got some stainless M6x1-30 bolts and lock washers. They only needed to be 20m long though. Worked fine though.



When the spark arrester came I realized that there could be a problem with a seal sealing on the side that has the screen and I was right, it didn't want to seal completely





So off it came. I decided it needed either a solid surface to seal against, which would be best, or a surface that the soft gasket could press into and seal. I didn't have anything around that shop that I could fill the screen surface side with that wouldn't either burn away or melt out so I decided to sand about 1/2 way through the screen in hopes the gasket could then deal with it.

Here it is sanded with 100G w/d paper on a block .



That and a little patience and letting it heat up while slowly tightening the bolts did the trick. Now I'm legal again. I am hoping this will put a few ounces of back pressure back as I think it was dangerously close to needing a programmer.

You keep it up, you might get the nickname MoMod. I will have to look into this for myself.

Looks good. Probably sounds good too.

Man that is pretty cool can't wait to hear the sound!! 

[2015 Z Force 800 53/Trail EPS]

Man that is pretty cool can't wait to hear the sound!! 

LOL..Its not too loud, just a little throatier. I'm still waiting on that mushroom filter. Tracking says it in CA somewhere. I need to get this thing out and test some of these mods...bad!.. hehe 

We started using Polaris snowmobile exhaust springs on the mufflers. They are twice the thickness as the stock springs & short, which gives the connection a nice solid tight fit.

I did a similar thing to my X8

Sounds pretty good. Nice work.

I think I'm going to do this too, and then put a little chrome tip on it for some bling! Lol
Seriously though good job! I've sent you messages on YouTube a few times asking you questions I'm glad I found you on here!

[2015 Z Force 800 53/Trail EPS]

I think I'm going to do this too, and then put a little chrome tip on it for some bling! Lol
Seriously though good job! I've sent you messages on YouTube a few times asking you questions I'm glad I found you on here!

I think I'll be doing the same but one thing I think I found is it may be at the edge of the injection system to not run lean. The plugs are running a little whiter and the exhaust is running a little hotter. The water temp isn't up though so it isn't much. I think I need a couple of ounces of back pressure back and I am hoping the installation of the spark arrester will give that back. You guys might wait for my update before doing it. It does run better though...

Good work. I made a complete exhaust system for my Grizzly, from the header all the way back to a snorkel. I tried twice to make a spark arrester my self. I used what appeared to be stainless steel both time, but both times it burned out. You should have better luck with this.

[2015 Z Force 800 53/Trail EPS]

Good work. I made a complete exhaust system for my Grizzly, from the header all the way back to a snorkel. I tried twice to make a spark arrester my self. I used what appeared to be stainless steel both time, but both times it burned out. You should have better luck with this.

I hope so. It's an actual HMF Spark arrester but it does her pretty hot..so hot it already blued the new tip as you can see. Hopefully it has given back enough backpressure so it's not as lean. It has changed it's running characteristics so it has done something.   

Watch "CF Moto Z8 testing upgraded pipe and engine chip" on YouTube
https://youtu.be/tM9Q8mYg26w
This pipe sounds pretty badass! I saw one other video from this guy and he says it is a race pipe from somewhere in Australia. I'll try to find a link. It's such an open design though,  I'm afraid you would have to have some type of chip to alter your air fuel ratio.

[2015 Z Force 800 53/Trail EPS]

The added slight restriction of the spark arrester put mine back in the range of the control system..but just. Any less restriction and a chip will be required.

The added slight restriction of the spark arrester put mine back in the range of the control system..but just. Any less restriction and a chip will be required.

The two brothers exhaust needs a good flowing air filter to go with it and absolutely MUST have a chip. Check your plugs even stock and youll see they are too white. They runs these things with a EPA forced 14.7 AFR to pass emissions. I've got mine running at 12.7 right now and love it. I still have some tuning to do, but it smells good now too ;-)