361 Shootout

[timberwolf]

Cylinder base turned down 0.018 and piston poped up 0.025 with 40 deg shoulder.

Cleaned up casting flash on piston as well.

 

[Terry Syd]

Wow, that is pretty. You removed some of the cylinder at the transfers, was that to assist in porting or to unshroud the piston (or both).

Nice work on the piston to get it to flow. You might even want to trim some of the extra metal off the outside of the wristpin hole, I doubt that the circlip needs that much metal to hold it in.

That looks fast just sitting there!

 

[timberwolf]

It's not quite right yet, RPM is a little lower than it should be and compression a little lower than is should be.

Running not bad though about .1 seconds faster than the other 361, but it should be a little quicker.

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Was really pushing on the second cut.

A few pics, muffler inlet before opening it up to match the flange, piston and cly.

 

[Terry Syd]

What about bumping up the crankcase compression a tad to push the powerband higher?

 

[timberwolf]

I think there is something else going on. I did find 10 pounds of compression, the decomp button was leaking a little.

A couple of changes in mind.

1 redrill a smaller and slightly relocated passage in the intake. there is a slight fuel pooling problem and tilting the saw front to back after ideling can make it stall.

2 increase exhaust durration about 4 degrees.

3 increase compression about 5-10 psi as raising the exhaust a little further will lower it some.

 

[mtngun]

redrill a smaller and slightly relocated passage in the intake. there is a slight fuel pooling problem and tilting the saw front to back after ideling can make it stall.

Thanks for experimenting with that little hole, TW. Now we know what it is for.

 

[ronT2]

Great thread timberwolf!

What kind of rpms is it turning in and out of the cut?

I like how you lengthened the upper rear transfers. I’ve tried it on a couple of my saws but not to that degree, I always worry about losing port velocity.

 

[timberwolf]

Only 14,200 or a little more out of the cut, I would have expected closed to 15,000.

For keeping it as a good usable worksaw this is a better approach to the intake than plugging the vent, rock stable idle no matter how much shaking or tilting. Just roughed it, still a little finnishing to do.

 

[Zombiechopper]

that's weird. I've got 15000+ with tons of four stroke on mine and not near as much tweaking done to it. Mine is max width ports, upper transfers similar to yours and lower transfer windows opened a bit. I've got mine at .018 squish without a popup. all stock timing. Is something with the timing hurting your RPM?
Just wondering why the revs are topping out on that saw

 

[timberwolf]

Yeh, it is strange, I'm going to swap another stock carb on and check that, maybe swap on another coil just to be sure. Power is there, just unloaded RPM seems a bit low and I would like to know why as the porting should be letting it rev up more.

 

[Terry Syd]

That transfer work took a lot of meat out of the crankcase and increased the volume. I'm still wondering if an increase in the crankcase compression might be warranted.

With the increased transfer area you provided, I don't think you have to worry about narrowing the powerband with some more CC compression, the existing powerband would likely just shift up higher in the RPMs.

Stuffing the crank pin is easy enough, and if you can get a couple of sealed bearings for the crank, it might be worth the experiment. You could always pull one or both bearings out later.

 

[timberwolf]

I tried it with a cylinder with much less removed on the transfers, about same RPM which is making me suspect either coil or carb.

There is not alot of volume inside the pin to stuff, 1mm tapered pin. Also I would worry about lack of cooling from the inside of the pin, These pins get enough heat to turn them interesting collors as it is.

 

[timberwolf]

A little tweaking on carb and a little cutting time and it has picked up some.

RPM still in the mid 14K range but it is cutting smooth and strong so not going to complain.

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[Trigger-Time]

That makes me smile

What wood is that?.......and has it been cold enough up there for the wood to be frozen?





TT