Hard to believe 9 years has past since I started running the 550 xp. It has been and still is one heck of a 50cc saw and has been stone reliable typically cutting 6 to 20 cord of firewood per year. I thought I'd share some things I have learned over the years of running her and the chains I trend towards.
Saw:
The Muffer Mod that is well documented is the only modification to the 550xp. The muffler has a bone stock appearance - including the spark arrestor screen, so nothing crazy. This is a great mod when done properly and nothing slows the saw down running an 18" bar.
Bar and Chain
I started out running the Woodland Pro NK bar and their 20NK chain. It is a solid combination for the money and I think I bought 10 boxes back when I made the switch to NK chain.
I ran and still have some Oregon 95TXL (NK) and that stuff runs nice, holds up well and held an edge much better than the 20NK - BUT - it was a bugger to file. Steel is very hard. I ran this on the Woodland NK bar.
Then I played with running some standard kerf chain on the Woodland NK bar. The Husqvarna H22 seemed to work well, but I fell in love with the Husqvarna H23 Full Chisel even though the only bar I had was the Woodland NK bar. When the Woodland NK bar finally gave up the ghost, I went with the 582075372 Husqvarna X-Force Pro Laminate bar and absolutely loved this bar. (I don't think it's availiable in the US anymore)
I stayed with the stock pin and never tried the 8 even though I had thought about it several times. With the muffer mod - I suspect it could pull it with no problem.
The Husqvarna H23 Chisel chain running on the Husqvarna X-Force Pro Laminate bar has been a great setup for me. The NK bar in some way seems to be a good option even though the H23 is a non-NK chain as it allows me to toss on a worn down NK chain when I get to the logs on the bottom laying in the dirt. (If I don't have the little Stihl MS230 with carbide chain with me)
I typically run 3 tanks and then touch up the H23 using the Stihl 2 in 1 tool (makes for lazy filing) and then drop the rakers a touch more. (5 more swipes with the flat file if the flat file touches). The steel is semi-hard but files ok. It cuts quick and holds an edge well, yet never bogs the saw in full 18" cuts in Oak. (It would prior to the muffler mod). I wouldn't recommend lowering the rakers like I do as the saw is agressive and feeds itself into the wood.
I do plan to try out the SP33G and would really like to get my hands on some Stihl 23RS Pro, but the Shihl chain just confuses me to no end. I have seen comments on the 23RS Pro being the best, yet try and find a loop. As far as a bar, I will probally go with a Husqvarna X-Force Bar 597649672 or Oregon Speedcut TXLB when the 582075372 Husqvarna X-Force Pro Laminate bar wears out. It's no longer listed or I would get it again. I still may try an 8 pin someday.
Of my current 3 saws - Stihl 064 - Husky 550XP - Stihl MS230, The 550XP with H23 is my go-to for bucking firewood.
Been trolling this forum a long time learing from all of you - I thought I should share where I am at with my setup with what I do.
If anyone has anything to add... I welcome anything you wish to share.
Thanks all for the great advice and discussions over the years