ORIGINAL: FlatSpin
ORIGINAL: Ernie Misner
I would like to see how it responds with the mac's black muffler, one piece unit. We are talking the extra volume version for the 55AX and 60NX. My 55AX's really come alive with this extra volume version muffler since it is larger than the .46 version.
If a certain pipe is tuned for glow, I don't know if that tuning is necessarily optimal for the same engine in gas.
You read my mind! I was thinking the same thing and will see if my OS 55AX MACs muffler will fit. If so, I might have some stats for you on Sunday (wx permitting).
Dave
I couldn’t wait for the weekend and decided to see what the MACs muffler would do. I switched to an APC 12x6 and got 10900 RPMs out of the stock muffler on the ground. At this altitude, I guess that is about right as we typically get an approx 15-20% performance decrease over sea level. I then put my OS 55AX MACs muffler on the Evolution. It fit the mounting bolt pattern OK, but I saw at least 1700-1800 RPM decrease over the stock muffler. The most I got out of it was barely 9000-9100 RPMs, but after about 2 minutes, the RPMs suddenly decreased to a “surging” 7600-7800. No amount of needle adjustments brought it back up and I even took off the muffler and remounted it two times just to be sure it was on correctly. Same results each time of upper 7K RPMs. So, in reality, I saw about 2800 RPM decrease from the stock muffler. This was just a gee whiz experiment with a muffler I had on hand. I hope another after market muffler designed for this engine will do better. You got to give the R&D guys credit, they designed the stock muffler for optimum performance.
Interestingly enough, I gained about 900 RPMs on the stock muffler by disconnecting the muffler pressure line. When the pressure line was on the muffler nib, the RPMs dropped to about 10000 but removing it caused an immediate increase to 10900-ish. Has anyone else seen this?
Dave