Go to www.arboristsite.com and do a search for muffler mods. That topic has been discussed in detail there on various saws.

If you can stand the flaming. I don't go there anymore.
The 455 is a new emission compliant stratocharged design and may not respond to the standard muffler mods.It will be interesting to see what Walker, EHP and others can do with them.

Hi blueseatx,

I don`t know anything specifically about the 455 but I can offer you the advice that opening the outlet of your muffler to around 80% of the exhaust port area of the cylinder and then enrichening the air/fuel mixture will make your saw run stronger, cooler, and longer. When opening the muffler make sure that no internal baffles obstruct the exhaust flow.

How do I know that muffler mods will work on your saw? Because they work on all modern saws because the manufacturers are intentionally backing up the unburnt gases in the exhaust in an effort to burn them and lower emissions. According to the US EPA, up to 30% of the fuel charge drawn into a two stroke engine is expelled through the exhaust without being burned. There is also a high likelyhood that your saw is adjusted on the lean side which not only reduces it's emissions but also it's ultimate power and will make your saw run hot. This is how a lean sieze happens in an extreme case and in less extreme cases you just have accelerated internal wear to the engine.

Enriching the fuel/air mixture will involve opening the hi speed needle on the carb. This may require that you remove the screw travel limiters, make the adjustments, and then re-install the limiters or you may do as many others have done and trim the limiter ears off the screws for complete adjustability. Trimming the ears is also considered tampering with emissions controls so be forewarned that if you do this and then need to bring your saw to a dealer for a repair and he notices the altered ears, he will be required to place new limiters on the saw.

Canguy, isn`t the 455 built similar to the 340/345/350 in that it has a horizontally split crankcase? Unless it has a seperate cylinder it will not be a good candidate for engine modification. I have a modified 575 that was improved dramatically but it still is not as powerful as a good 372. Maybe if I do some intake work it will improve.

EHP can be found at his own site now, ehp.com. There is a link on his page to chainsawperformance.com where you won't find any fighting or nonsensical suggestions on how to modify your saw with a nail file, just guys who are building, racing, and working with true hi performance saws and chain. You will also find that many of the Timbersports and G.O. Games guys are posting there. Check it out.

The 455 does have a horizontally split crankcase similar to the others but the cylinder design and carbretion are completely different. There are two intake ports and an extra transfer port. The second ports draw air only into the combustion chamber to allow a complete burn of that 30 percent you mention.I believe the muffler is also equipped with a cat which limits mods.The carb may also be fixed jet, I have not looked closely at it.

Hi Canguy
I understand about the various ports and such but I'm not completely convinced that the extra 30% is burned because the power is not there as if it were and these new saws will run longer on a similar volume of gas indicating to me that they are making use of a smaller initial volume of gas in the engine and possibly oxygenating the exhaust gas to help it more completely combust before exiting the muffler.

The catalyst in the muffler is not an issue when the muffler is modified if done right. What is a severly limiting factor in regard to modification is that the squish cannot be closed to a more optimal width and the compression is not easily raised on a horizontally split case. Compression is horsepower and a wide squish is detonation. None of this however makes the 455 anything less than a very good saw.

Thank you for the suggestions everybody. I drilled a 1/2" hole next to each of the existing exaust outlets and two more at the top and bottom of the exaust manifold. The saw is running much cooler then it did before, and it does not bog down as easily when cutting through a large tree. It is 2x's as loud now, but that does not bother me. Thanks again for the help!!!

Dremel & hand drill , socket set , job done !