I'll try to get all the info in here that I can remember. Matt wanted a saw a little better than a normal woods port. So we set out to do it. After talking with some race guys I had a better idea of what to change to get results. We used a stihl 046 piston turned backwards. The ring ends are in the wrong place to run it correctly. If you did the ends would be right in the transfers. You have to make a spacer. We did no machine work to any parts on this. That's the kind of nice part of it. You can take it all out and put a stock piston back in and be in business if you don't like this. I can't see any one not liking it unless you want to run the Dolmar HD filter kit. We swapped a carb from a 372xtorq into it along with a carb boot. It tilts the filter and doesn't let the intake elbow go back into the little rubber to hold it down like oem. The linkage needs a little trimming and you have to pull the plastic piece off the zama and put it on the other carb after drilling another hole to orient it correctly to get full throttle travel and not hold the butterfly open too much. The impulse hose has to be lengthened about an inch. The fuel line will be a little long and I trimmed a 1/4" off it to keep it from kinking. There's a lot of trial and error on clocking the carb to get all of it to line up at the same time.
Here's the muffler mod I did. I uncrimped the muffler to pull the cage out. I cut it off the base where it bolts on to keep that as a spacer. I opened it up to match the cylinder. The straight out the front is the quickest way to get exhaust out so that's what we did. On a true work saw I wouldn't make the opening as big there and I'd fab up a deflector to direct it to the side somewhere. I threw one picture in of the degree wheel setup I use.
I ended up opening it up even more. It made it louder but it's cutting strong so I guess it needed it.
Very nice Mike. I sort of specialize in what some call 'FrankenSaws'. Some here don't get the idea that 'you can put it back to stock' value. They just don't get the value of what you did over porting. Nothing wrong with porting but it is an irreversable process. Yes you can revert back but not without spending a lot more $ than just a new piston, or better yet removing the spacer and putting back the original piston. With a little time pouring over specs you can come up with lots of these types of things. Stihl 028S piston in a Husqvarna CP 55, a 52mm BBK using a Stihl 064 piston on a 372XP. Great job, I take my hat off to you! KRL
Yep. That's the spot that gets the hottest part of the exhaust hitting first. Stihl was on to something with the dual port front covers.
Yep... Seen a Solo with the same cut out!! This is a thread I have been waiting for and never thought would be released! ! Thank you Mike and Matt! My hat is off to both of you! That is one bad 7900!!!
Thanks. It was several more hours involved in it over a woods port. It was a fun project and I may do it again soon.
Just trying to get a higher rpm band for cutting small stuff. He was wanting more towards a race/play saw than work.
Taller and a little bigger windows. You would think there's a ton of material removed to get it to run great. On most it's not necessary. I think Matt said in the other thread it's pulling over 12k in the cut with an 8 pin.
The shim was most probably to avoid turning a popup. Shim would have also changed the port-timing slightly, since he mentions above that squish was 0.035, it was obviously not to achieve 0.020 squish.
