the fact remains that a 42cc saw will beat it in stock form which is what 95% of saws are.echo 490(this would also apply to the CS500P) 2.8hp
With a simple muff modd and tuned right they run like a 3.8 to 3.9 hp saw plus have a wide power band. Plus they are light Steve
just adding a little to the whole muffler mod idea. I own a cs-400, 4300, 5105, 6100, 7910, 6800, 111, 115, and a JD 66SV plus soon to add a 5600 to my fleet of personal saws. the only one of those that isnt completely stock is the 4300 and it is just a simple cat delete. I also think your being pretty optimistic on a simple muffler mod getting them to 3.9hp. 3.2 maybe but not 3.9.