CASE VOLUME DISPLACEMENT ? / Introduction

[SHOVELHEAD]

I joined OPE a couple weeks ago after seeing Chainsaw Jim's 357XP Hybrid Build, & thought WOW I need to follow up on this Build.

It stared last Fall when I'd Purchased a J-red 2159 with a new OEM Top for my midsize saw.
When I got it back to the shop to investigate it further I'd realized the new top wasn't the 2159 but a 2156.

Still A great runner though, & Really like the handling characteristics of it.

So I stared looking in to see if this was a good thing or not?
&
That's when I found Jim's Build.
And decided (I HAVE) to add one to my J-red collection. (THANKS JIM) LOL

So I placed a Wanted add here looking for a non running saw, with no Luck.

Soon I was @ a saw shop & carried home ( 2 ) 2159's & (1) 2156 for my project,
A week later I returned back to the shop looking for used mufflers to fit a 272XP Cylinder.
That was interesting to say the least, seeing as I didn't even own a Cylinder as of yet
(Thank you lwhaples) (Found using the wanted adds)
and the only thing I new to look for was a 9-3 bolt pattern.
Just before leaving the shop with my newest collection of misfit muffles,
Ipicked up a 2nd nice 2156 runner for $75.00 that I purchased from a customer.
Wright time Wright Place !

So back to the ? @ hand ?
This is going to be a 72.2 cc Build.
I would like to know if I should go with More case volume or Less? 2159 / 2156
&
Why

Pros & Cons

Thanks

Great Forum here
I've spoke Several times by Phone in the distant past to Randy & Scott
AKA
MASTERMIND & TREE MONKEY
Both great knowledgeable guys, Thank you

 

[SHOVELHEAD]

@Mastermind

 

[Mastermind]

Moved to Chainsaw forum.

Welcome to OPE sir.

 

[Chainsaw Jim]

I'd rather build another with the non stuffer 359 to compare before I try giving any pros or cons about this particular subject of case volume.

 

[Marshy]

So, do I understand this right... You are putting a 272 piston and cylinder on a 2159 or 2156 case and you want to know which case would be the best (more or less case volume)?

 

[Adirondackstihl]

I’d go with the larger case in this scenario

 

[Heffalump]

Having run Jim's 272/357 Mutant, the power to weight is what really makes it righteous. I ran more than one 6 cube machine, and more than one ported machine that day, but the nuts on that light little monster blew me away.

So, what is the weight difference between the cases?

 

[SHOVELHEAD]

Moved to Chainsaw forum.

Welcome to OPE sir.

Thanks

 

[SHOVELHEAD]

So, do I understand this right... You are putting a 272 piston and cylinder on a 2159 or 2156 case and you want to know which case would be the best (more or less case volume)?

That's correct,
I'm wondering if it would be beneficial to have more case volume (2159)
Being that it's going to be 72cc saw.
I have both 2156 & 2159 @ my disposal
Just looking for the best outcome.
Which to use and what are the benefits?

 

[SHOVELHEAD]

Having run Jim's 272/357 Mutant, the power to weight is what really makes it righteous. I ran more than one 6 cube machine, and more than one ported machine that day, but the nuts on that light little monster blew me away.

So, what is the weight difference between the cases?

There's little to know difference between 2156 & 2159,
Same chassis just tops are differed cc
& port styles .

 

[Heffalump]

So then, where does the increased crankcase volume come from?

 

[Marshy]

So then, where does the increased crankcase volume come from?

Crank stuffers in the 2156/357 saws.

 

[SHOVELHEAD]

The above is correct.
No stuffers on the 2159 / 359
So this series saw will have the most case volume

 

[Mastermind]

Installing a larger top end will increase case volume.........right?

 

[Marshy]

Yes but.... to stuff, or not to stuff. That is thy question.

 

[Heffalump]

(About to put my lack of knowledge out for the whole world to see......)

WTF is a crank stuffer? I thought we were talkin' chainsaws....?!?!

 

[SHOVELHEAD]

They in this case (no pun intended )
A compost disc that's attached to each of the crankshaft to give it a full round effect instead of a lobe.
In making the crank into a full round you displace the surface area (case volume) and therefor make it smaller.

 

[Adirondackstihl]

Installing a larger top end will increase case volume.........right?

Theoretically.....I think so.
You’re adding volume below the intake floor.
Am I correct?

 

[jackjcc]

I wonder if the 576 has crank stuffers? If I remember right the 562 and 550 have them and the purpose was to reduce case volume so that the stroke of the piston was more directly moving air. If that makes sense, less case volume meant there was less space for fuel charge to sit about. Low volume meant that movement in the piston created more flow of fuel charge up the transfers.

If that’s all true then you would want case stuffers, but the 550 and 562 have less low end end grunt and that may be a result of the stuffers.

I did some light research and this scientific paper seemed to find very little difference for flow rates between large and small crankcase volume http://www.bridgestonemotorcycle.com/documents/crankcase_volume6.pdf

The paper identified inlet pipe length as a serious contributing factor to flow rates of fuel charge into and through the engine. I wonder if anybody has changed the distance between cylinder and carb on race chainsaws or maybe little thought has been put into it.

So many variables at play too, I really think without building the hole system specific to one of those cases then crank volume shouldn’t play a big role.


Sent from my iPhone using Tapatalk

 

[Mastermind]

Theoretically.....I think so.
You’re adding volume below the intake floor.
Am I correct?

Well if the bore is bigger......then the piston will displace more volume above, and below. Right?