Big CC Chainsaws a thing of the past or will new models come out soon?

[Robin Wood]

Does anyone watch Iron horse on youtube? I think he's aiming for lighter pistons, not sure about the crank though. A lighter piston would probably improve acceleration but would it change the torque figures? 

Lighter piston will give more rpms and tq, weight on top vs bottom difference is important. The greater the difference the more tq and rpm it will have, 268 piston in 372xp oe is a common mod in canada. Those guys love that setup, 268 is 12g lighter than 372 oem piston. With pop up it loses even more weight. Here's a pic

[Robin Wood]

 

Another interesting thing about the mac kart engine was someone found a way to increase power by welding extra weights on the crank. It became common at some point and i think uncle lee had that done in one of his mac 101b cart motor, it pulls hard. Untill the weld came off and halted the motor, no damage i think. He managed to fix it back, the video of it running and seizing is somewhere in youtube

[Robin Wood]

Nearly Stubby, been here before havent we....
 
Inertia is what something heavy has - its the resistance of the heavy thing to change speed. You have to put energy into or take out energy from the heavy thing to change its speed. A flywheel is a special case because it's a rotating thing,  the flywheel effect that we understand is called "moment of inertia". The same rules apply though, to make it spin faster you put energy into the flywheel, and take energy out to make it go slower.
Through a single engine cycle, energy is put into the flywheel (combustion) and taken out (over coming compression, powering the power take off etc). Importantly, a flywheel can not produce power on its own. It can give up some of its energy over several engine cycles but the result is that the engine slows down. "Big" flywheel with high moment of inertia has lots of energy so slows down less if you take out same energy per cycle.
Moment of inertia is calculated as mass multiplied by radius squared, easy to work out for the pendulum, not so easy for flywheel, crank, rod and piston. But there are bits of kit to meaure moment of inertia and a CAD systm will have at calculating it. As mentioned above you can have a big diameter, light flywheel having same moment of inertia as a small diameter, heavy flywheel.
 
 

Precisely inertia, hard to gain and hard to lose. Majority of tq from a motor will come from the heavy reciprocating weight, tq x rpm is hp. If you can spin heavy stuffs fast enough that motor will generate lotsa power. But manufacturers tend to put governor and rev limit to prevent the motor going way up and getting jolted or stopped suddenly. That'll cause damage, crank can get snapped. Thats why almost all new big saws have rev limit of some sort.

Ms880 walbro wg12 is limited carb, ignition is limited at 10.5k
3120xp is even worse no H jet on carb limited at 9k and ignition is limited as well
Cs1201 is carb limited at 10k

[shavey]

1 hour ago, Robin Wood said:

Uncle Lee is the guy to talk when it comes to dolmar 166, i think it could have lower bore size like 52mm maybe. But stroke is 48mm i remember that, uncle lee has a hybrid 166 with 090 top end. They got a video of it running 72" bar in upstate gtg couple years back.

Uncle and I go way back, i sent him 3 units of 1201 and took me few years to find a good used 1200 to complete his big echo collection. Half of the 166 exist on the planet could belong to him, he had like 30 over 166s! At some point

He loves muscle saws, sent him a NOS Jonsered 920 last month. Last i heard his collection was close to 500 saws

Yes he loves his big saws that 166 was liked by everyone and so was the 1201 

He received that 920 about the the same time I received the 7300

[Robin Wood]

Yes he loves his big saws that 166 was liked by everyone and so was the 1201 
He received that 920 about the the same time I received the 7300

Lol its a small crowd eh mate?
You're andrew?

[Rough Hewn]

Precisely inertia, hard to gain and hard to lose. Majority of tq from a motor will come from the heavy reciprocating weight, tq x rpm is hp. If you can spin heavy stuffs fast enough that motor will generate lotsa power. But manufacturers tend to put governor and rev limit to prevent the motor going way up and getting jolted or stopped suddenly. That'll cause damage, crank can get snapped. Thats why almost all new big saws have rev limit of some sort.

Ms880 walbro wg12 is limited carb, ignition is limited at 10.5k
3120xp is even worse no H jet on carb limited at 9k and ignition is limited as well
Cs1201 is carb limited at 10k

What are these figures Robin?
Rpm is higher than 10.5krpm on 880.
[emoji106]

[Robin Wood]

What are these figures Robin?
Rpm is higher than 10.5krpm on 880.
[emoji106]

Rpm
Yes i stand corrected, should be 11.5k on the 880 i believe? Too many variants on the literature among the 1124 series. Ms880 with ms361 coil swap gains good deal of power, ignition advance built in 361 coil feels alot better than stock 880 limited coil. Albeit it trying to bite when pulling over

[Rough Hewn]

Rpm
Yes i stand corrected, should be 11.5k on the 880 i believe? Too many variants on the literature among the 1124 series. Ms880 with ms361 coil swap gains good deal of power, ignition advance built in 361 coil feels alot better than stock 880 limited coil. Albeit it trying to bite when pulling over

It’s 12.5krpm I think?
Yes, common mod for the 880 is the unlimited 361 coil. Heard lots of good things about it[emoji106]

[bmp01]

23 hours ago, Mrblue5000 said:

Does anyone watch Iron horse on youtube? I think he's aiming for lighter pistons, not sure about the crank though. A lighter piston would probably improve acceleration but would it change the torque figures? 

No.

Not by itself.

If there's a change in compression, change to combustion chamber shape,  swap to single ring or some other thing then maybe but weight change by itself will not give more power.

Plus it might screw up the balance of the engine and you'll feel it as extra vibration - those counter weights on the crank didn't get to be the size they are by accident.

 

Edit: Meteor pistons seem to work well, often tighter squish by a few thou over oe piston. Piston skirt length isnt always same as oe piston. Small changes but sometimes these little bits add up in the right direction.

Edited November 27, 2020 by bmp01

[Robin Wood]

It’s 12.5krpm I think?
Yes, common mod for the 880 is the unlimited 361 coil. Heard lots of good things about it[emoji106]

Im not even sure mate, carb and coil seems to be limited at different rpms? Too many carb variants, tilly and walbro. The one im working on with 361 coil turns 13k with slight burble at top, thats as far is I'd like to go on a big saw like this