Porting the 361 Big Bore

[blsnelling]

Tonight I began the process of porting the 361BB prototype that I have. The P&C look as good as new upon disassembly. The goal of this saw is to be competetive at a GTG level. It will also be used as a firewood saw. I took measurements on the saw tonight and will post them here. I would appreciate any feedback you guys might have on what numbers I should go with. Here's where it stands right now.

1. Squish = .017, no base gasket. That's how I've been running it.
2. Compression was 185 cold after only a little run time. I forgot to check it tonight.
3. Exhaust 105*
4. Transfers 125*
5. Intake 71*
6. Blowdown 20*
7. Exhaust width 1.00", can go to 1.25".
8. Intake width 1.03", can go to 1.25".

The exhaust seems aweful low, but this saw 4-stroked out to15,800. If I went to 98*, I would have to raise the roof .075"! To get to 95* would require raising it .115"! I can't imagine taking that much out. What numbers would you go with?

The exhaust port shape is pretty nice the way it is. The intake floor is very round. A lot of improvement to be made there. As you can see, I've got room to widen quite a bit, nearly .250" on both sides.

Whatcha think?

Exhaust Port

Intake Port

Crown after running 15,800.

 

[Wortown Mick]

Great pics.

The exhaust port traced onto the piston doesnt look symmetrical but im guessing its just the surface of the piston messing with me.

Keep us updated as you work I like to read and see how you guys do things to make an attempt at learning myself.

 

[blsnelling]

Please do not post in this thread. I'm moving it to the Chainsaw forum. There seems to be no traffic here. Mods, feel free to delete this thread.