Is compression king?

[RI Chevy]

These

Awesome Jason! The Stihl stayed right with that 346! LOL

 

[Genius]

Make sure you have a good grip on the starter handle, I wouldn't want you to lose any f-i-n-g........uh, nevermind........

Peace to you too cuzin hippie

 

[CR888]

My strongest running saws are 175-190psi comp. Not sure there is a magic number but I don't feel bigger is always better. I think some focus too much on what's only a part of the puzzle in the tuning process. We some what naturally think 'bigger is better' in other aspects of tuning like timing, port size, carb size etc. No one wants to 'retard' their timing they want to 'advance' it no matter what it really needs.

 

[Redfin]

Nope. Not king. Two 262 XP's,same compression,same squish ,same carb,same muffler,same builder(me),different jug. One runs good. But the other one runs better .

And there is your proofff.

Must be something "just right" with the 064,066 series with that compression..

The variables just come together in that range.

I do agree 170-215 is a good range for most work saws.

I have done quite a few 60cc and less they noticeably like comp in the 200-215 range.

200 psi on 50cc is a lot less heat than 200psi on 80cc plus..

I would like to know the "why" smaller bores dont mind the higher comps.

Follow my thinking, the larger bores compress more volume to a certain psi that a smaller bore would but...

The larger bore also has a larger centripital mass to carry the piston around back up to tdc to repeat the process.

 

[sawmikaze]

My strongest running saws are 175-190psi comp. Not sure there is a magic number but I don't feel bigger is always better. I think some focus too much on what's only a part of the puzzle in the tuning process. We some what naturally think 'bigger is better' in other aspects of tuning like timing, port size, carb size etc. No one wants to 'retard' their timing they want to 'advance' it no matter what it really needs.

All the high comp saws ive ran sound like they just fight themselves and not a single one impressed me..they dont have the zing i like , "personal" opinion.

 

[jmssaws]

Loop scavenging is key
Make it want to suck and blow more and you make power

Smaller saws don't have to be high compression but the small bore and stroke allow it to tolerate it more.

It gives a tourqe feel to a tourqeless motor.

 

[jmssaws]

185lbs

 

[sawmikaze]

These

Thems are good runners buddy.

 

[Red97]

And there is your proofff.

I would like to know the "why" smaller bores dont mind the higher comps.

Follow my thinking, the larger bores compress more volume to a certain psi that a smaller bore would but...

The larger bore also has a larger centripital mass to carry the piston around back up to tdc to repeat the process.

The real explination is way above my pay grade.

The way I see it is real similar to the doc,

Smaller bores seem to handle the heat better, and fight the pumping losses better than larger bores.

May be way off. I will say 240 is no gain in a standard woods ported saw. That I know for sure...

 

[Stihlbro]

I'm not very good with words on the internet, my post don't always come out right , but I know thru experience cranking compression can be misleading. The internet tell you you more is better. I'm a believer there is more of a formula to determine what you need.

1.) What is your elevation?
2.) What are you cutting?
3.) What kind of chain you using? Bar length?
4.) How you operate a saw?
5.) What are your physical limitations?

Most saws that are factory hot rods are harder to get gains out of versus the typical pro rated saw. They generally have more cranking compression. In other words, if you tell me you got 200 plus compression and are four stroking at 15k plus, then bring the saw to Mastermind in December and let me run it.

I often relate saw experiences to automotive scenarios. I remember the day of the 5.0 mustangs and lingo and how it changed thru that era. I've been thru the truck scenes too. The moral of this as we all want a truck that pulls like a Mack, rides like a Cadillac but run like a Super charged mustang. We saw enthusiast what a small saw that pull like ole home lite, speed of a race saw but yet handle like limbing saw.

Ok, I may have ranted for a bit but to answer the question of cranking compression, in all my experiences the more compression is not always most powerful.

 

[Termitebuffet]

185lbs

Looks good [emoji2]

Zoo City Sawz

 

[RI Chevy]

Is it possible to have high compression, low RPMs for a chain saw?

 

[redtractor]

Higher compression generally needs higher octane fuel to get the detonation to fire.

You usually need high octane race fuel to get detonation.

You've got you're thinking backwards. Higher octane fuel is harder to ignite. Low octane fuel would ignite too early as high compression would heat it up and fire it off like a diesel engine.

 

[RI Chevy]

Then why do race cars use race fuel?

 

[RI Chevy]

Lower octane fuel will not allow a 14 to 1 motor to run.

 

[jmssaws]

Jchin couldn't start his 064 anymore so I built him a 150lb beast.
The saw had 175lb stock

 

[RI Chevy]

Nice job! Still pulls really well.

 

[Magic_Man]

Then why do race cars use race fuel?

I fought the same battle as you having grown up around big v8 engines my whole life. You have to throw all that out the window, 2 stroke engines and saws in particular are a completely different animal.

 

[RI Chevy]

Ok. Thanks. I was thinking it was me.

 

[redtractor]

Lower octane fuel will not allow a 14 to 1 motor to run.

Low octane fuel will fire at the wrong moment causing detonation (not the good kind), poor performance to the point of not running at all, and even damaging the engine. Higher octane will wait until the the time is right.