Might be on to something. Recently watched a Dyno pull on a 440. Haggerty….since you are a mopar guy. They pulled 8 degrees initial timing out incrementally during runs due to mid range knock. Results , slightly less hp, slightly more torque and a better power range for both with a higher overall rpm range for both. They basically moved the entire power curve higher, although hp was less. They were testing other mods as well, but this is pertinent to this discussion.

I believe i know why that makita 6100 runs better with high exhaust roof 96* is because that cylinder has a very small combustion chamber. So at the higher exhaust roof it lets the saw run faster and make higher compression at a higher rpm. Like race saws with a 2 piece head. The spark knock I would try higher octane fuel maybe 94 or colder plug first before the flywheel timing.

Love the theorizing! You're theory about the timing of that saw makes sense to me👍🏻 The last few months I've been questioning timing advances in saws without major port # changes. Making me want to time some cuts of saws I've advanced, then put timing back to stock and compare.

"I'm going to try and leave it alone", said that myself each time I finish modding my Echo CS-490 and I've been into it about 5 more times now (and still considering still digging back into it)

I like your thinking on intake flow on this build 👍😎

I believe the combustion chamber and squish band arrangement in the Makita is an efficient design. That combined with very good mixing due to high velocity and turbulence in the intake/transfer cycle leads to great atomizzation and a extremely fast flame front travel. So basically the pressure peak is short and sharp. That's the reason they respond to a high exhaust roof. On your 560 your peak pressure is now before 10 degrees after tdc. Retarding the ignition is not going backwards, your combustion event has become more efficient, you just need to retard the timing to put your pressure peak back in the proper location.

I enjoy the timing discussion, my own experience has shown me that lowering the cylinder thus increasing compression changes the ignition timing. The cylinder is lower in relation to when the ignition timing is set to make spark based on the flywheel position. On a high revving 2 cycle the dynamic compression does not appear to be linier, so ignition timing required for optimal power or torque varies base on where the power is made in the rpm range. Every make and model saw is it's own animal depending upon the engine mod's that have been performed. My G366 based on the way I built it wanted 3 to 4 degrees less timing than the way it came stock to run without spark knock or popping in the cut. My saw running backwards like dyno Joes G366 did was resolved with this slight timing change.

The squish band is there to push fuel into the center of the combustion chamber.

Great topic. Consider the Echo 8000. Low (115°) stock exhaust opening to provide the large amount of torque that the engine makes on the least amount of fuel. No ping at 25° advance.

Excellent

Like the pulling chain

Higher exhaust roof on 2 strokes gives lower compression due to when the rings seal... I get some of what you are saying about torque tho... especially in the cut 👍😎 hope to see something amazing

Maybe you try the Bpmr8Y Plug which is colder to compensate It. So it runs cooler and has less self ignition.

you can build one for torque and put a big sprocket , will be interesting

Does the 10thousands band at the squish ring, was it put there for flow reasons ? Like having a 3 angle grind job on 4 stroke.

colder plug could help spark knock

I think a taller piston is needed for the 590/620. 2mm taller above the wrist pin and 2mm more skirt. That way you could cut squish, taper or pop-up cut the piston, cut the base for desired squish without worry of Freeport. Then port as desired and trim the skirt as needed for clearance or timing issues. Would open up a lot of possibilities on that platform.

Second time watching this one 😊

Thx i had a light bulb go off in my head

Retarding timing also increases torque since maximum cylinder pressure is at a later crank degree and therefore it has more leverage to push the crank. About the torqy saw I'd guess to start with a long stroke, low ex roof and late timing. But this you already knew already but maybe it helps some viewers. Good vid B keep em coming

👍

Hey

Ресурс двигателя интересно на сколько снизится? После данных доработок

I have a 590/620 that i am working on right now. .020" out of the band, .020" squish, 106° exhaust, no spark knock, and it revs to 14k. 80° intake, 124° transfers

Low roof, short blowdown high torque? Add a reed valve and you got a Homelite or many other vintage saws. 106 with 16-18 degrees of blowdown was common on the vintage saws. Compression was all over the place. Basically the smaller the displacement the higher the compression usually got but not always. There were a lot of factors. Some of the bigger saws would hit 190 pounds but 130 was very common in the 60cc range. Some 40cc models would be closer to 200 pounds so there are a lot of things to consider.

Dollar 6100 is made by Germany engineerings, atmosphere power.

👍🆙BigGuy

To me a high compression and torque don’t belong together!?! Think about a tractor. We want a tractor not to stall and a stall happens when the piston can’t squeeze the squishy air above the piston. So a tractor has heavy flywheel and low compression so u can’t stall it. U can’t get both without losses. Harley guys do it but u see how that goes sort of limited in hp.