Part Four: Compression

[Simondo]

I think you're right on the money with that line of thinking. My 372 at 180psi doesn't try to stretch my fingers as bad as my stock 288 did at 150psi. The volume of air being compressed must be the difference in this example.

Thinking,(I know, never stops) is there another way to look at compression? Case in point; the 266 and 281 were/are notorious for being hard to pull over just as they came from Husqvarna. Is this the result from a larger amount of trapped swept gasses vs just being squashed a lot more, because the latter doesn't seem possible to me. So in other words does the exhaust port roof play an important part of the final outcome as much as the squish band tolerance?

Are the starter cord reels different diameters when full of cord ? or the connection to the starter palls bigger /smaller diameter . Im thinking ..Leverage .

 

[XP_Slinger]

Are the starter cord reels different diameters when full of cord ? or the connection to the starter palls bigger /smaller diameter . Im thinking ..Leverage .

The 288 pulley looks bigger to my eye. Because of its starting manners I expected to see 180psi on the gage before I tore it down for rebuild. Nope, it was 150psi on the nose.

 

[Simondo]

The 288 pulley looks bigger to my eye. Because of its starting manners I expected to see 180psi on the gage before I tore it down for rebuild. Nope, it was 150psi on the nose.

You would have thought it should be ...just thought i would throw the idea out there

 

[Stump Shot]

Are the starter cord reels different diameters when full of cord ? or the connection to the starter palls bigger /smaller diameter . Im thinking ..Leverage .

I think that can be debunked by the fact that the 266 has the same starter as the 272, and a 272 won't vapor lock at half pull like it's smaller cousin.

 

[XP_Slinger]

Maybe it's just a difference in ignition timing. The old dogs may be advanced a little more, not as nudered by EPA guidelines.

 

[XP_Slinger]

You would have thought it should be ...just thought i would throw the idea out there

And it was a good one. I was and still am honestly baffled as to why it was literally breaking my balls at that pressure. Had the tank handle between muh legs while pulling it over the first time . Even checked my gage to verify it was at least close to being accurate and it was.
Now I have a decomp on it, no mo problems

 

[Mastermind]

Some saws just gotta be drop started.

 

[XP_Slinger]

Some saws just gotta be drop started.

You sir have a point. That 288 likes to try and show me who's boss. Lol

 

[Mastermind]

I had to make a video to show a customer how to start his high compression 064 once.

 

[rattler]

I had to make a video to show a customer how to start his high compression 064 once.

I love it. Dang 288 can be a handfull.

Sent from my SM-G935V using Tapatalk

 

[Mastermind]

I love it. Dang 288 can be a handfull.

Sent from my SM-G935V using Tapatalk

He sent the saw back.....thought it was screwed up. It fired up on the second pull. No decomp....

So, I figured he might need to see how to safely drop start it.

First......set the chain brake....

 

[rattler]

I have started drop starting everything it's Easy on me and the saws

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[Stihlbro]

I will agree with earlier post of a balance between performance and a well behaved saw. Once you have experienced it, it really hard to explain.

I think you can have too much compression. It generates heat, puts extreme load on the rotating assembly. Can it shorten the life of a saw, yes? Is there a magical number, I dont have a solid way to answer other that.

I've ran many good performing saws with pop up, and have dabbled with cutting squishband. If one is superior, it is too many variables and gets down to saw specifics.

I've seen speckles of what I think is detonation but reading up on it mostly related back to quality of fuel or ignition.

Most Stihl manuals state 89 octane or higher. I've tried all, even the true fuel, motomix, vp and regular pump gas. Hard to beat 87 octane properly mixed.


Alcohol needs more compression to get the same btu output as gas. It take roughly 3 times more volume to compare to gas. It does have more of a cooling feature than gas. This could be a plus.

Nitro methane does not take as much compression depending on the nitro content. Things get real using it!!! But my only experiment is with trying to go fast for short periods of time. Ambient temperature plays a huge factor.

E85 was mentioned and it is one I've never tried but the small gains made with alcohol, it is worth exploring. Not for a daily user but for gtg's.

If we could tap into Dennis Cahoons mind, the knowledge and experience he has would be phenomenal to this site. I don't think he will put much on the internet though based on past experiences. If he is saying match fuel to the compression, my thoughts follow the concept of the more compression the higher the octane needed. Higher meaning slower burning but adding oil slows that down and the cost of the higher octane does not seem feasible to a daily user or seasonal firewood cutter. Certainly too expensive for the logger.


I've tried to measure combustion chambers with blue windshield washer fluid and a graduated syringe. I quit because I was hard to get accurate readings.

 

[Brewz]

My 181 has a wide squish band and a small chamber.
Its a *b-word to start. Not checked compression but I figure its up there.

I like my saws with 170 to 200 psi
I find they wind up faster, make good wide range power and start easy even with well advanced timing.

 

[rattler]

I will agree with earlier post of a balance between performance and a well behaved saw. Once you have experienced it, it really hard to explain.

I think you can have too much compression. It generates heat, puts extreme load on the rotating assembly. Can it shorten the life of a saw, yes? Is there a magical number, I dont have a solid way to answer other that.

I've ran many good performing saws with pop up, and have dabbled with cutting squishband. If one is superior, it is too many variables and gets down to saw specifics.

I've seen speckles of what I think is detonation but reading up on it mostly related back to quality of fuel or ignition.

Most Stihl manuals state 89 octane or higher. I've tried all, even the true fuel, motomix, vp and regular pump gas. Hard to beat 87 octane properly mixed.


Alcohol needs more compression to get the same btu output as gas. It take roughly 3 times more volume to compare to gas. It does have more of a cooling feature than gas. This could be a plus.

Nitro methane does not take as much compression depending on the nitro content. Things get real using it!!! But my only experiment is with trying to go fast for short periods of time. Ambient temperature plays a huge factor.

E85 was mentioned and it is one I've never tried but the small gains made with alcohol, it is worth exploring. Not for a daily user but for gtg's.

If we could tap into Dennis Cahoons mind, the knowledge and experience he has would be phenomenal to this site. I don't think he will put much on the internet though based on past experiences. If he is saying match fuel to the compression, my thoughts follow the concept of the more compression the higher the octane needed. Higher meaning slower burning but adding oil slows that down and the cost of the higher octane does not seem feasible to a daily user or seasonal firewood cutter. Certainly too expensive for the logger.


I've tried to measure combustion chambers with blue windshield washer fluid and a graduated syringe. I quit because I was hard to get accurate readings.

Well said...

Sent from my SM-G935V using Tapatalk

 

[Stihlbro]

I wondered once, why manufacturers choose what they did for compression. After several discussions with family and friends, we came to a conclusion that the saw is built to run all over the world. Differemt altitudes/elevations, species of wood, different fuels and climates. At least compression it one thing the manufactures allow us to manipulate to suite our needs.

Although, some of the newer saws come with more, dolmars and solo's come to mind, I would say on an average most saws stock are in the 135 to 150 psi perform well with a 20 to 30 psi bump.

 

[Mastermind]

I will agree with earlier post of a balance between performance and a well behaved saw. Once you have experienced it, it really hard to explain.

I think you can have too much compression. It generates heat, puts extreme load on the rotating assembly. Can it shorten the life of a saw, yes? Is there a magical number, I dont have a solid way to answer other that.

I've ran many good performing saws with pop up, and have dabbled with cutting squishband. If one is superior, it is too many variables and gets down to saw specifics.

I've seen speckles of what I think is detonation but reading up on it mostly related back to quality of fuel or ignition.

Most Stihl manuals state 89 octane or higher. I've tried all, even the true fuel, motomix, vp and regular pump gas. Hard to beat 87 octane properly mixed.


Alcohol needs more compression to get the same btu output as gas. It take roughly 3 times more volume to compare to gas. It does have more of a cooling feature than gas. This could be a plus.

Nitro methane does not take as much compression depending on the nitro content. Things get real using it!!! But my only experiment is with trying to go fast for short periods of time. Ambient temperature plays a huge factor.

E85 was mentioned and it is one I've never tried but the small gains made with alcohol, it is worth exploring. Not for a daily user but for gtg's.

If we could tap into Dennis Cahoons mind, the knowledge and experience he has would be phenomenal to this site. I don't think he will put much on the internet though based on past experiences. If he is saying match fuel to the compression, my thoughts follow the concept of the more compression the higher the octane needed. Higher meaning slower burning but adding oil slows that down and the cost of the higher octane does not seem feasible to a daily user or seasonal firewood cutter. Certainly too expensive for the logger.


I've tried to measure combustion chambers with blue windshield washer fluid and a graduated syringe. I quit because I was hard to get accurate readings.

I wondered once, why manufacturers choose what they did for compression. After several discussions with family and friends, we came to a conclusion that the saw is built to run all over the world. Differemt altitudes/elevations, species of wood, different fuels and climates. At least compression it one thing the manufactures allow us to manipulate to suite our needs.

Although, some of the newer saws come with more, dolmars and solo's come to mind, I would say on an average most saws stock are in the 135 to 150 psi perform well with a 20 to 30 psi bump.

Thank you Joey for these excellent posts.

 

[rattler]

Couple chamber pix one k&s one Mahle

 

[Termitebuffet]

Compression is good ,extreme compression is extremely good ....imho [emoji200]

 

[Mastermind]

You can use the word "gooder" here Randy.