Is compression king?

[Red97]

Amen Brother Randy.

Let's all remember:

Chainsaw Specific Output Formula:

TORQUE x RPM/5250 X 100/saw builders calf +thigh diameter

Yep, I'm screwed...
Entered the Calc, got back a negative number...

#noskinnylegshere

 

[drf256]

And the word for the day is...

I learned the word from Obama.

The kinda word you know when you've never had a real job and your schooling stopped at 30th grade.

 

[Mastermind]

Our world is full of thin skinned people that can't handle being wrong. Luckily we have gathered together a group of guys that can handle having their ideas scrutinized. That's why we are not only doing well here, we are thriving.

 

[Stump Shot]

Friction, plays a significant role in the ability to make RPM. Played around with a 340Rotax engine put .020" under sized piston and rings in it. If you could ignore the piston slap it made over 11,000 RPM on the tach. Good for racing but not so good for general use. Piston could not transfer heat to the cylinder and would overheat till it blew a hole in one of them during extended use.
A cousin of mine built a half Sachs, half Rotax single with a hand fitted piston and no rings at all. Before every race it had to be taken apart and the piston greased allowing it to start with enough compression, being good for one drag race, then repeat process.
So it kinda depends on what you're doing as to what you can get away with. To try and translate to the power saw world, I would think a racing saw should be able to take less friction than a work saw would because of the different usage/run times. Surely though this would throw a giant wrench into the compression tester readings, as they would seem really low.

 

[Deets066]

Friction, plays a significant role in the ability to make RPM. Played around with a 340Rotax engine put .020" under sized piston and rings in it. If you could ignore the piston slap it made over 11,000 RPM on the tach. Good for racing but not so good for general use. Piston could not transfer heat to the cylinder and would overheat till it blew a hole in one of them during extended use.
A cousin of mine built a half Sachs, half Rotax single with a hand fitted piston and no rings at all. Before every race it had to be taken apart and the piston greased allowing it to start with enough compression, being good for one drag race, then repeat process.
So it kinda depends on what you're doing as to what you can get away with. To try and translate to the power saw world, I would think a racing saw should be able to take less friction than a work saw would because of the different usage/run times. Surely though this would throw a giant wrench into the compression tester readings, as they would seem really low.

I would put a used ring in if I wanted less friction, but you go too far undersized and transfer is coming around on the upstroke and exhaust gas on the down stroke. Mixing em is what you want to stay away from

 

[drf256]

I would put a used ring in if I wanted less friction, but you go too far undersized and transfer is coming around on the upstroke and exhaust gas on the down stroke. Mixing em is what you want to stay away from

Or only a used ring on the lower groove.

Best of both worlds

 

[Stump Shot]

I would put a used ring in if I wanted less friction, but you go too far undersized and transfer is coming around on the upstroke and exhaust gas on the down stroke. Mixing em is what you want to stay away from

Not to say you should throw away your piston rings LOL, the examples I gave were just goofy stuff we tried to go fast back in the day. Just trying to point out that a racer should be able to get away with a bit more than an actual user, in the topic of friction. Also that while you may have a high compression ratio, might not translate to a high compression reading if trying to reduce friction. That's all. Experimentation obviously required.

 

[Stump Shot]

Maybe more guys can post like Deets066 did as to what they did to their saws to reduce friction and maybe some kind of semblance can be made of it.

 

[Stihlbro]

So it kinda depends on what you're doing as to what you can get away with.

Truth!!

 

[Terry Syd]

Carbs are my new obsession.

Now that you've got your head around carbs, let's see what you can do with the reed block on that 6100.

By the way, as long as we are discussing compression ratios, I got a 'ding!' about the offset combustion chamber on the 6100. I went back to Blair and found where he discussed various combustion chamber designs and squish velocity. Sure enough, the offset combustion chamber had around twice the squish velocity of a central chamber. He specifically mentioned it in regards to 'stratos' for mixing in order to get a more homogeneous mixture.

I'll be REAL impressed if you can get a boost port in that saw! When you do, I'll send you a check for a saw - you'll have saved me a heap of work!

 

[jmssaws]

I post most everything I try and I try something new everyday, what I'm doing today that's working i may not use tomorrow.

I bought a new 460 in 2007 and ported it and it was the first 460 I ever did,no telling how many I've done since and I've yet to build one stronger,got close yesterday with one that's ported the complete opposite of mine but close is all.

Makes me wonderif somewhere in the last 10+ years if you loose your way but eventually find your way back.
Strange and confusing business this is.

 

[Red97]

It's a miracle if I do the same thing twice.

Even if I try.

We are trying to simplify a very elaborate engine. Way too many variables to "mesure" to get just one aspect dialed in.

If something works for your personal preference don't stray too far from it without good reason.

Feel free to try new thing as post the findings. That is what helps everyone get a better idea.

Just don't build echos, they be mostly uncharted territory

 

[RI Chevy]

With all the talk about compression, has anyone ever tried to do any work on the crank? Maybe a little more or a little less counterweight? Maybe balance it? Microfinishing the bearing locations? I can go on, but just posing the question.

 

[Deets066]

With all the talk about compression, has anyone ever tried to do any work on the crank? Maybe a little more or a little less counterweight? Maybe balance it? Microfinishing the bearing locations? I can go on, but just posing the question.

Full. Circle

 

[RI Chevy]

Lol.

 

[jmssaws]

It's a miracle if I do the same thing twice.

Even if I try.

We are trying to simplify a very elaborate engine. Way too many variables to "mesure" to get just one aspect dialed in.

If something works for your personal preference don't stray too far from it without good reason.

Feel free to try new thing as post the findings. That is what helps everyone get a better idea.

Just don't build echos, they be mostly uncharted territory

I've never built to a set of numbers but I build saws that the cylinders vary a lot,don't think I've ever built 2 alike.

I change shape and angle and size more than height and everyday I'm looking for just a little more.

The more I mess with shape and size and angle the more I see that the height is not the most important thing.

 

[Stump Shot]

Our world is full of thin skinned people that can't handle being wrong. Luckily we have gathered together a group of guys that can handle having their ideas scrutinized. That's why we are not only doing well here, we are thriving.

Also if you think about it, there really is no right or wrong to building something to "race" so to speak, only what wins. One fella will have success trying something and the other will fail doing the same but in a different application. I like to think the best rewards are to those unafraid to try new things, weed out what fails and move forward. This is why the sharing of ideas works so well here, most aren't skeered to put parts on the line to see what happens. This is when the best things happen.

 

[jmssaws]

Also if you think about it, there really is no right or wrong to building something to "race" so to speak, only what wins. One fella will have success trying something and the other will fail doing the same but in a different application. I like to think the best rewards are to those unafraid to try new things, weed out what fails and move forward. This is why the sharing of ideas works so well here, most aren't skeered to put parts on the line to see what happens. This is when the best things happen.

I've said it before that if your worried about ruining a cylinder or can't afford to replace it then you shouldn't be grinding on it.

I've got a big shelf of fails.
Most are mine but I have had to buy 3 cylinders for a customer's saw,*s-word happens.

 

[Nitehawk55]

Muffler mod is all I will do with my saws if I feel it's under performing , I can't be bothered with anything beyond that .

 

[Mastermind]

Now that you've got your head around carbs, let's see what you can do with the reed block on that 6100.

By the way, as long as we are discussing compression ratios, I got a 'ding' about the offset combustion chamber on the 6100. I went back to Blair and found where he discussed various combustion chamber designs and squish velocity. Sure enough, the offset combustion chamber had around twice the squish velocity of a central chamber. He specifically mentioned it in regards to 'stratos' for mixing in order to get a more homogeneous mixture.

I'll be REAL impressed if you can get a boost port in that saw! When you do, I'll send you a check for a saw - you'll have saved me a heap of work!

In a few weeks I'll have a 6100 of my own to play with Terry. Then we will try new and different stuff. I promise.

Makes me wonder if somewhere in the last 10+ years if you loose your way but eventually find your way back

And this ^^^^^^ is why I started digging back thru my old notes.

With all the talk about compression, has anyone ever tried to do any work on the crank? Maybe a little more or a little less counterweight? Maybe balance it? Microfinishing the bearing locations? I can go on, but just posing the question.

I had a 046 with a highly polished crank once. It was by far the strongest 046 I've ever owned. Related? I'm really not sure.