I agree! I've been using the MACS muffler on my Evo 10cc since about February without issue. I have 3+ gallons thru it and it is running strong. The max RPMs I have gotten with a 13x4 APC is ~14900. (DX-8 w/Tlm). I am a sport flyer, so I am not interested in worrying about every detail to squeeze out the last bit of HP, etc. In other words, YMMV, but for me the MACS is just fine on this engine.

Dave