Echo cs 490 porting

[bikemike]

Empty muffler can on the 490.



Do you think that the stright ducts are limiting the rpm tho?

As for the chamber, yeh not quite sure what they were thinking. Other than the offset helps keep the heat down on the ex side a bit. Why a triangle shape?

How big is the exit hole or tube?

 

[drf256]

Anyone here know the max temp an exhaust port reaches? May be a dumb question.

 

[RedFir Down]

chadihman on AS shared this with me in a PM.
"First 1 min idle. 198°f at the muffler and 164 on the cylinder. Then 1 min under load at 9k.. Muffler 720 cylinder 315. After 2 min under load at 9k. Muffler 770 cylinder 330. 3 min muffler 765 cylinder 295. After 4 min muffler 768 cylinder 305 and the same patter for the remainingtime under load. I then idled it for 1 min and the muffler was back to 326 and thecylinder 250°f."

 

[drf256]

OK.

SO Low temp Aluminum braze (700*) may hold up.

 

[Red97]

OK.

SO Low temp Aluminum braze (700*) may hold up.

If I was going to try what you are thinking....

I would lay the jug on one side, build a dam out of tinfoil/ clay and or jam a copper bar in the gap. Use a cast iron skillet and melt down a couple trashed pistons. Then pour in between the roof of the port and the fin... like filling the egr ports in an auto head.

Think that would be less heat shock to the jug, once it cools in that space it can't go anywhere.

Just my .02

 

[Red97]

Easiest muff mod ever..

How big is the exit hole or tube?

That big., hole is bout 3/4 and tube is about 1/2 sticks in 1 1/4 ish.

 

[drf256]

OEM346 vs. Echo 490 Jug




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[drf256]

Sent from my iPad using Tapatalk

 

[Red97]

So whatcha thinking sir?

Bolt on the 346 jug lol

 

[David Young]

Empty muffler can on the 490.



Do you think that the stright ducts are limiting the rpm tho?

As for the chamber, yeh not quite sure what they were thinking. Other than the offset helps keep the heat down on the ex side a bit. Why a triangle shape?

The swoop of the closed port saws like stihls and the pro huskys.
They run better I think scavenging efficiency.

 

[drf256]

If I was going to try what you are thinking....

I would lay the jug on one side, build a dam out of tinfoil/ clay and or jam a copper bar in the gap. Use a cast iron skillet and melt down a couple trashed pistons. Then pour in between the roof of the port and the fin... like filling the egr ports in an auto head.

Think that would be less heat shock to the jug, once it cools in that space it can't go anywhere.

Just my .02

Tig could warp the jug and pop the plate. I'm not sure that 700* will.

 

[drf256]

The swoop of the closed port saws like stihls and the pro huskys.
They run better I think scavenging efficiency.

I'm trying to wrap my head around this one.

Air doesn't like to change direction. I see the husky transfers above helping the charge turn and adding volume. The tunnels look smaller on the 346. The port openings are larger. The intake and ex port are strikingly similar externally to the 490.

The 346 has narrower longer transfers than the 490. So more resistance to flow and more volume, but more velocity.
The 490 has shorter larger transfers, and the charge has to make that sharp turn.

As per @tree monkey , the 346 likes 117* of transfer duration, or a height of 121.5*. So 16.5* blowdown. As the 490 transfers ain't flowing like the 346 ones above, I'd venture to say that the 490 is gonna need even more transfer duration than the 346 likes.

I'm gonna shoot for 108/122-123/80 on my saw.

 

[bikemike]

Keep those pics coming. Good info here I miss the good threads like this

 

[bikemike]

Yeah the husky transfer and intake look to be wider than echo

 

[David Young]

Al,
great post, I honestly don't have any answers just thoughts and guesses.

the ducts on the 490 are huge so lower velocity. maybe the 346 needs the sweep because of higher velocity and the entrance is more violent.

are you going wide on the exhaust?

"As per @tree monkey , the 346 likes 117* of transfer duration, or a height of 121.5*. So 16.5* blowdown. As the 490 transfers ain't flowing like the 346 ones above, I'd venture to say that the 490 is gonna need even more transfer duration than the 346 likes. "

I think you are right on this if you try to increase pressure in the transfers they are going to get sloppy and do a worse job. The transfers need a longer duration but to work the exhaust has to have enough blowdown and I understand you are backed up against a wall there.

maybe the transfer ports need to be opened in width and height to match the duct size? Then you can keep the transfers lower. I can see on a 346 how it would not work unless you opened the whole duct like Randy said.

if you could get a tight fitting piece of aluminum to go over the top of the exhaust manifold. it doesn't have to be welded solid just tacked in a couple spots.

I think your numbers are a good guess on what to do. It may like more intake because of the smallish carb. time will tell

 

[Red97]

Just to play devil's advocate

http://sawhawgz.com/showthread.php/4337-Just-Another-Old-Crappy-Poulan





Yes it is a little larger saw, around 60cc with more carb.

But strictly looking at transfer design, I cannot see why the stright ducts will limit the rpm of this saw.

I think it is strictly a volume thing. The way I am looking at the 490 transfers are the ducts are rather large, holding good volume and have to squeeze through the smaller ports thus increasing velocity.

I am shooting for 106, 125 I think that little extra blow down will help raise the pressure in the transfers before they open.

 

[David Young]

Just to play devil's advocate

http://sawhawgz.com/showthread.php/4337-Just-Another-Old-Crappy-Poulan





Yes it is a little larger saw, around 60cc with more carb.

But strictly looking at transfer design, I cannot see why the stright ducts will limit the rpm of this saw.

I think it is strictly a volume thing. The way I am looking at the 490 transfers are the ducts are rather large, holding good volume and have to squeeze through the smaller ports thus increasing velocity.

I am shooting for 106, 125 I think that little extra blow down will help raise the pressure in the transfers before they open.

I think those are completely different they have a lot of sweep. But I believe you are right there is a volume thing at the root of this.

 

[Red97]

I think those are completely different they have a lot of sweep. But I believe you are right there is a volume thing at the root of this.

Think I'm going to spend some time with the long burr in those transfers to get a little more "swoop" at the top.

I am really enjoying this discussion, thank you all for contributing..

 

[bikemike]

Just to play devil's advocate

http://sawhawgz.com/showthread.php/4337-Just-Another-Old-Crappy-Poulan





Yes it is a little larger saw, around 60cc with more carb.

But strictly looking at transfer design, I cannot see why the stright ducts will limit the rpm of this saw.

I think it is strictly a volume thing. The way I am looking at the 490 transfers are the ducts are rather large, holding good volume and have to squeeze through the smaller ports thus increasing velocity.

I am shooting for 106, 125 I think that little extra blow down will help raise the pressure in the transfers before they open.

I like nice jugs

 

[bikemike]

Any more thoughts into making 2 of those transfer ports wider like the husk