Chainsaw Porting Theory

[mdavlee]

Those numbers are pretty close to the old school race saws with pipes.

 

[Barneyrb]

Now Randy, to a left handed batter a big ole hangin curve ball looks like a flying ribeye steak floating in

 

[Mastermind]

I think it's important to see how different timing numbers are for applications other than saws. I've read Blair, Bell, and Jennings, and studied motorcycle designs. Nothing that I have found yet in any of those resources crosses over well to the mufflered work saw.

 

[Miller Mod Saws]

I think it's important to see how different timing numbers are for applications other than saws. I've read Blair, Bell, and Jennings, and studied motorcycle designs. Nothing that I have found yet in any of those resources crosses over well to the mufflered work saw.

There's your next calling buddy! Mastermind work saws. The book!

 

[Mastermind]

There's your next calling buddy! Mastermind work saws. The book!

You give me way too much credit Carl. I don't have any clear answers on the WHY.

I've just done a lot of saws......

 

[awol]

I think it's important to see how different timing numbers are for applications other than saws. I've read Blair, Bell, and Jennings, and studied motorcycle designs. Nothing that I have found yet in any of those resources crosses over well to the mufflered work saw.

This is very true, and I think the reason being is the difference in bore to stroke ratio, and lack of tuned pipe.

For chainsaw performance, I'll take a mm of stroke increase over a mm of bore increase every time.

 

[Miller Mod Saws]

You give me way too much credit Carl. I don't have any clear answers on the WHY.

I've just done a lot of saws......

Just add the world theroy and wing it. All will be good!

Mastermind Work Saws Theroy!

Fixed it!

 

[jmssaws]

This is very true, and I think the reason being is the difference in bore to stroke ratio, and lack of tuned pipe.

For chainsaw performance, I'll take a mm of stroke increase over a mm of bore increase every time.

You and me both.

 

[Simondo]

You give me way too much credit Carl. I don't have any clear answers on the WHY.

I've just done a lot of saws......

A lot of saws = learning =experience= knowledge = confidents= more saws = more knowledge.

 

[shorthunter]

I've never seen carbon in the transfers but perhaps on a shot p&r you could get some.

If the P&C were "shot" we would see carbon staining on the cylinder walls.

I can get you a few pictures of carbon staining below the exhaust port if you would like?

 

[shorthunter]

I mostly work on one particular model but am very interested in the quad port design.

All I've done is a few 372 390 and 395's
So I'm listening.

Beats me

The last two posts are why there's carbon in transfers.

I really wish that you would approach this discussion with an open mind. You indicate that you have only done a few saws and that you don't know about squish velocity, yet you won't accept the fact that transfers backflow.

If everyone would listen instead of rejecting ideas that aren't their own, there would be a lot more information sharing on these forums. There are several great saw builders who refuse to do build threads for the simple fact that they get tired of people telling them that they are doing it wrong.

To answer your "beats me", saw builders cut the squish band to increase squish velocity.

 

[beaglebriar]

 

[jmssaws]

I don't know exactly what you mean,when did I say I've only done a few saws?

I've ported 100's of saws,mostly 660's.

I cut the squish band to increase compression and if that increases squish velocity then kool.

 

[jmssaws]

If the P&C were "shot" we would see carbon staining on the cylinder walls.

I can get you a few pictures of carbon staining below the exhaust port if you would like?

P&r not p&c

 

[RIDE-RED 350r]

I think it's important to see how different timing numbers are for applications other than saws. I've read Blair, Bell, and Jennings, and studied motorcycle designs. Nothing that I have found yet in any of those resources crosses over well to the mufflered work saw.

This is very true, and I think the reason being is the difference in bore to stroke ratio, and lack of tuned pipe.

For chainsaw performance, I'll take a mm of stroke increase over a mm of bore increase every time.

Late to the party, and I fully admit that my experience based knowledge on porting theory and design for a desired power curve and RPM range is in it's infancy at best...

I would agree with you both on these points when comparing chainsaws to motorcycles/ATV's.. But I would also add that while your 2-stroke bikes and race ATV's have porting layouts that are designed to try and deliver as wide a usable power curve as possible while still being able to spool up well for the longer pulls. Expert builders like ESR, LED Performance, CT Racing and many others also do custom porting for different applications that focus on low-mid (MX) mid-top (dune/overall) and all out top end drag porting for drag racing and hill shooting. Since I have been starting to learn some tricks on these saws and as I am getting ready to start making small changes in port timing for my first time this weekend, I took one of my Honda 250r cylinders I have on stand-by down off the shelf and looked up it's skirt... After being so immersed in saw world in regard to porting theory these last several months, the layout of that 250r cylinder seems incredibly sophisticated! And when I stop to think about what it is built to do, it makes sense...

All of that said, I think it's fair to say that compared to bikes and wheelers a chainsaw is more of a 1-trick-pony. It needs to spool up quick, and have a power curve more focused on the top end of the RPM range. I would say it's probably comparable to a drag ported bike/ATV cylinder.

Alot of the same rules of porting surely still apply, but I think the methods are different and what might work well with a bike engine may not work with a saw and vice-versa.

For information's sake, stock 250r bore and stroke is 66x72 My ESR 350r is 78x72

 

[Al Smith]

With a chainsaw it really only has one power curve ,WOT .A MC has several depending what it's designed for plus it has gears .

Now of course if you want a torquer you long port ,rever raise it up .Good torquer ,more R's ,mid range .It just all depends on what you want it to do,cookie cutter or work saw .

 

[drf256]

I really wish that you would approach this discussion with an open mind. You indicate that you have only done a few saws and that you don't know about squish velocity, yet you won't accept the fact that transfers backflow.

If everyone would listen instead of rejecting ideas that aren't their own, there would be a lot more information sharing on these forums. There are several great saw builders who refuse to do build threads for the simple fact that they get tired of people telling them that they are doing it wrong.

To answer your "beats me", saw builders cut the squish band to increase squish velocity.

Who's rejecting any ideas?

It's a discussion. Everyone's entitled to their opinion.

It goes both ways.

Post a build thread of yours. We won't tell you why you're wrong.

I'm not a pro. I posted a build thread on an 024S. 14 pages and I only got constructive comments.

 

[MustangMike]

Size matters, but I'm not sure it matters much if it is from bore or stroke. A ported 460 will produce a lot more torque than a ported 440, and it is all bore and only about 8% larger.

 

[Four Paws]

Size matters, but I'm not sure it matters much if it is from bore or stroke. A ported 460 will produce a lot more torque than a ported 440, and it is all bore and only about 8% larger.

Not just bore...case volume.

 

[Mastermind]

Not just bore...case volume.

It's about balance....

And I've still got so much to learn.