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.
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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.