Someone getting an Echo cs 590 For X-MAS

[Four Paws]

These echoes have a longer stroke than their competition, and a smallish carburetor. They also have a torturous path through the muffler.

Do you think the restrictive exhaust tract has anything to do with the rather short blowdown?

What do you think the reason is for the extremely low stock exhaust?

 

[Red97]

These echoes have a longer stroke than their competition, and a smallish carburetor. They also have a torturous path through the muffler.

Do you think the restrictive exhaust tract has anything to do with the rather short blowdown?

What do you think the reason is for the extremely low stock exhaust?

Most 60cc have a hda series or equivalent it seems.

Really think the muffler has a lot to do with meeting decibel requirements. Just a mild mod these things are crazy loud.

Think the short blowdown is to keep the powerband low where they want it.

Low exhaust height, longer powerstroke. I believe to give the transfers more pressure to fill at the lower rpm.

Would love to hear your thought process.

 

[Four Paws]

The long power stroke definitely provides the signature echo torque, and in my opinion holds these saws down on rpm. This low exhaust basically requires the transfers to open later, so some of the spent charge can exit.

I think it would be beneficial to stick the piston in the jug and understand what the lower transfers look like at transfer open and at BDC.

It would also be beneficial to install the piston on the crank, understand how things look at BDC.

I like the looks of the intake port.

The case doesn't look overly "tight"...not like a 7900 that has long factory blowdown and only 1mm more stroke.

My approach at this point would be...look less at numbers and more at geometry. How things fit together and feed. I would target a few deliverables like .020" squish with a base gasket. I don't mind sealer, but I prefer a gasket. I would target compression in the 195 psi range...a little more or a little less is OK...but it keeps you from getting fixated on a certain exhaust timing number.

I feel like I am rambling, I will stop for now.

 

[Red97]

The long power stroke definitely provides the signature echo torque, and in my opinion holds these saws down on rpm. This low exhaust basically requires the transfers to open later, so some of the spent charge can exit.

I think it would be beneficial to stick the piston in the jug and understand what the lower transfers look like at transfer open and at BDC.

It would also be beneficial to install the piston on the crank, understand how things look at BDC.

I like the looks of the intake tract.

The case doesn't look overly "tight"...not like a 7900 that has long factory blowdown and only 1mm more stroke.

My approach at this point would be...look less at numbers and more at geometry. How things fit together and feed. I would target a few deliverables like .020" squish with a base gasket. I don't mind sealer, but I prefer a gasket. I would target compression in the 195 psi range...a little more or a little less is OK...but it keeps you from getting fixated on a certain exhaust timing number.

I feel like I am rambling, I will stop for now.

The stroke definitely helps with torque, don't see it as the rpm limiting factor. That is all up to the metallurgy. But lots of people are running longer stroke/heavier piston combos up in the 14k+ range.

I agree It is beneficial to see what the ports look like with the piston in various locations.

As builders we all tend to focus on certain aspects of the build. This is where it is nice to have a fresh set of eyes that may see/suggest something you don't think of.

With the cutouts in the transfers that adds a lot of volume to the case imo. Think that can be helpful with a smaller carb. Along with more intake timing.

This in my mind follows suit for a "as designed " lower rpm engine. Not necessarily a limiting factor.

Not thinking I will have the skirt to cut for a gasket.

I was thinking 200-210psi would be plenty for this saw.

Don't necessarily care about the ex number. I am just trying to base my findings from stock saw, to semi educated guess ported numbers. And find a correlation as to what did what.

Feel free to ramble away, may get me to see something I didn't think of.

 

[Four Paws]

The stroke definitely helps with torque, don't see it as the rpm limiting factor.

You misread...I said long power stroke (low exhaust) not long stroke. 37 mm is a gift!

 

[Red97]

You misread...I said long power stroke (low exhaust) not long stroke. 37 mm is a gift!

That I did.

And I agree..

 

[Four Paws]

Not thinking I will have the skirt to cut for a gasket.

You mentioned somewhere squish was .04x" with a .017 gasket. And, you had .050" of piston skirt until free port. Should have plenty of room by my math, unless you are going to cut base and chamber, which will drop your intake even further.

I would cut just enough to hit .020" with a gasket. You can always take more later. You can also widen the intake port if you feel you need more.

 

[Red97]

You mentioned somewhere squish was .04x" with a .017 gasket. And, you had .050" of piston skirt until free port. Should have plenty of room by my math, unless you are going to cut base and chamber, which will drop your intake even further.

I would cut just enough to hit .020" with a gasket. You can always take more later. You can also widen the intake port if you feel you need more.

The 590 in my video was set at .018 squish no gasket and band uncut. 170 psi.

I am going to cut the chamber in this one to get it in the 200psi range.

I don't think a bit more intake duration will hurt with the stock carb.

I'll get some stock port pictures up tomorrow. Along with measurements.

 

[drf256]

Joe and 4P, loving the tech discussion. Right up my alley.

My opinion my be right or quite wrong.

I'm a relative novice in this game, but I've found that I don't use Blowdown as a basis of where I want transfers. I do look back at it, after my plan, to make sure something doesn't seem really off.

I kinda do it based on case volume, transfer shape and volume and intake closing points. Also port shape and design. I don't think any one rule fits any particular engine.

I find I like lower exhausts. If I can fill the cylinder with more charge, I can take advantage of more of the pressure it builds from combustion.

I believe physically higher (numerically lower) transfers build better high rpm power but sacrifice low end torque. I see the potential for some back stuffing at low rpm when charge inertia can't overcome it.

I do believe many very high factory transfer saws are that was because of a very restictive exhaust. They need more time to fill the cylinder because of the back pressure.

I do like to think of the plume shape exiting the transfers. In my minds eye, I want it to be fat and directional. I think opening the exhaust side first makes the ribbon of flow thicker. Quads give ya the best of both worlds, lots to play with there.

Sorry if I'm rambling a bit. I'm a port flow nerd.

 

[drf256]

On those odd 490 uppers, I'd want both uppers opened simultaneously. My thinking is that the smaller main will help loop scavenging by directing charge upwards towards the intake wall. The shape, placement and size of those intake side uppers make the saw seem like more of a cross scavenged/loop scavenged hybrid.

 

[Red97]

Joe and 4P, loving the tech discussion. Right up my alley.

My opinion my be right or quite wrong.

I'm a relative novice in this game, but I've found that I don't use Blowdown as a basis of where I want transfers. I do look back at it, after my plan, to make sure something doesn't seem really off.

I kinda do it based on case volume, transfer shape and volume and intake closing points. Also port shape and design. I don't think any one rule fits any particular engine.

I find I like lower exhausts. If I can fill the cylinder with more charge, I can take advantage of more of the pressure it builds from combustion.

I believe physically higher (numerically lower) transfers build better high rpm power but sacrifice low end torque. I see the potential for some back stuffing at low rpm when charge inertia can't overcome it.

I do believe many very high factory transfer saws are that was because of a very restictive exhaust. They need more time to fill the cylinder because of the back pressure.

I do like to think of the plume shape exiting the transfers. In my minds eye, I want it to be fat and directional. I think opening the exhaust side first makes the ribbon of flow thicker. Quads give ya the best of both worlds, lots to play with there.

Sorry if I'm rambling a bit. I'm a port flow nerd.

On those odd 490 uppers, I'd want both uppers opened simultaneously. My thinking is that the smaller main will help loop scavenging by directing charge upwards towards the intake wall. The shape, placement and size of those intake side uppers make the saw seem like more of a cross scavenged/loop scavenged hybrid.

Al, I am also very green to saw building.

I tend to agree/follow many of the same thought processes you use.

I really need to get the pictures, and measurement's up to fuel this discussion.

This is what I love to see, a good healthy discussion. Sure to spark plenty of ideas on this particular model, some that surly aplies to others.

You guys are potentially receiving this saw, and it is good to hear the owners thoughts on how the saw should run.

 

[paragonbuilder]

This is a great discussion.
It seems sometimes we get fixated on numbers, but doing so it's easy to lose sight of how flow through the engine makes power.


Sent from my iPhone using Tapatalk

 

[Red97]

TDC

Mid stroke

BDC

Intake shape, I would say intake area is around 20% larger than exhaust.

Intake width 60% 27.3mm Exhaust width 54% 24.2mm Combined transfer open area 63% 16.5mm +11.6mm

 

[Four Paws]

I believe that your second and third picture are the same.

 

[Red97]

I believe that your second and third picture are the same.

Fixed that

 

[Four Paws]

Fixed that

Nice.

Now what does the side of the piston look like when installed on crank at BDC?

 

[Red97]

 

[Woodpecker]

I will say this somebody is going to be pleasantly surprised/very happy with this saw! I got a chance to hang out with Joe and run his ported 590. Very impressive saw!

 

[Red97]

I will say this somebody is going to be pleasantly surprised/very happy with this saw! I got a chance to hang out with Joe and run his ported 590. Very impressive saw!

Thank you sir, it was nice to run some saws and get a hands on opinion.

 

[Mastermind]

This is a excellent discussion.