Echo 490 to ported 4910…to cs-5484

[farminkarman]

First cuts with 4910

Massive improvement over stock but just not there yet

youtu.be

Ran better 4000’ lower, but still not great. Couldn’t quite keep up with a stock 261. At current power it feels a lot more like a ported 40cc saw and kind of peaky and irregular. I’m going back in.

Thinking I’ll take the primary to 124 and raise the exhaust to 105. Open to suggestions.

I would leave the exhaust down and try raising the primaries to 124 and secondaries to 127.

 

[Dolkitafreak]

Ported shindaiwa 492

youtube.com

More ex duration

 

[Red97]

Add some more duration to the exhaust and transfers.

102-104 and 124 -126 will probably get it running like you want. I'd still do the full 70% at the cylinder wall too even if you can't get it "straight" out.

 

[Ketchup]

Back apart.


I pulled numbers again, to be sure. 77.5/110.5/126-132. I guess I read the exhaust wrong.

Based on the piston I think it’s not got enough blowdown. I’m worried my case compression is weak too.

I’m going to drop the exhaust to 106 and re-work the secondary flatter to 128. Also going to single ring.

 

[farminkarman]

I would leave the exhaust down and try raising the primaries to 124 and secondaries to 127.

Back apart.
View attachment 364943View attachment 364944

I pulled numbers again, to be sure. 77.5/110.5/126-132. I guess I read the exhaust wrong.

Based on the piston I think it’s not got enough blowdown. I’m worried my case compression is weak too.

I’m going to drop the exhaust to 106 and re-work the secondary flatter to 128.

That should wake it up a bit.

 

[whitesnake]

Back apart.
View attachment 364943View attachment 364944

I pulled numbers again, to be sure. 77.5/110.5/126-132. I guess I read the exhaust wrong.

Based on the piston I think it’s not got enough blowdown. I’m worried my case compression is weak too.

I’m going to drop the exhaust to 106 and re-work the secondary flatter to 128. Also going to single ring.

Hey I found your problem. There’s a hole in your piston.

 

[Ketchup]

Hey I found your problem. There’s a hole in your piston.

Haha! That’s just a beauty mark.

Ran it today with the new timing and transfer shape. Better but still pretty weak. Going back in again. Not sure if I want to raise the transfers more or not. Currently 77.5/106.5/126-128. Tempted to go to 125 flat.

 

[huskihl]

Might try lowering your intake floor some. I can’t remember for certain, but it doesn’t seem like those carburetors are very big. Might need more time to fill

 

[Dolkitafreak]

Might try lowering your intake floor some. I can’t remember for certain, but it doesn’t seem like those carburetors are very big. Might need more time to fill

Dinky little WT’s.

 

[Duane(Pa)]

Begs the question: What carb mods/models can turn up the wick?
Mine seems to wind up pretty well, but the man that built it (Dyno Joe) is on record saying the little carb is a limitation.

 

[Ford3000]

Begs the question: What carb mods/models can turn up the wick?
Mine seems to wind up pretty well, but the man that built it (Dyno Joe) is on record saying the little carb is a limitation.

Well the 4910 Joe had on his dyno ran really strong, using its stock carb, would that carb
fit the OP 's saw, @Red97 may know.

 

[Ford3000]

Might try lowering your intake floor some. I can’t remember for certain, but it doesn’t seem like those carburetors are very big. Might need more time to fill

Could the problem be the intake is already too big, and reducing the velocity,
and, would more velocity also help to push out the exhaust gas up to a point,
and also result in a sucking effect up the transfers or at least lower any opposing
pressure to the new charge coming up the transfers.

 

[huskihl]

Could the problem be the intake is already too big, and reducing the velocity,
and, would more velocity also help to push out the exhaust gas up to a point,
and also result in a sucking effect up the transfers or at least lower any opposing
pressure to the new charge coming up the transfers.

It could be. Hard to say without small incremental changes. And once you go wide, it’s typically not very feasible to get it back narrow. There has been discussion before by some who think you should go wide before you go down with the floor and give up case pressure. If velocity suffers by going wide, it may very well be better to go with stock width and just add some duration.

To the latter part of your question, I don’t think intake velocity directly has much to do with transfer velocity or pushing out spent exhaust.

 

[Dolkitafreak]

I think a dub-ya J makes ‘em run pretty spiffy…

I don’t widen the intakes much on these, just add duration. Did one with max width ports and same durations, no quantifiable gain for me

 

[Red97]

98% of the time I don't mess with the intake. Just transfers and exhaust.

 

[Ketchup]

98% of the time I don't mess with the intake. Just transfers and exhaust.

Same here. Sometimes I get a wild hair though. In this case I wanted to direct intake flow towards the transfer lowers. I got the idea from your winged 395 intake video. Probably not as effective in this smaller bottom fed engine.

Well the 4910 Joe had on his dyno ran really strong, using its stock carb, would that carb
fit the OP 's saw, @Red97 may know.

Same carb, unless I’m mistaken. I pulled down some HDA and EL carbs, but they would be annoying to fit. RWJ seems race only terrain. The 590 carb is also too large and bad layout. There are some WTs out there with the larger Venturi, but simplest solution is just bore the Venturi a tad and drill the jet. Living up here in the ether, more fuel isn’t what I need.

Could the problem be the intake is already too big, and reducing the velocity,
and, would more velocity also help to push out the exhaust gas up to a point,
and also result in a sucking effect up the transfers or at least lower any opposing
pressure to the new charge coming up the transfers.

Sluggish intake is possible but examining the port there is no sign of pooling. Looks really good. I’m not sure a sluggish intake matters that much in a work saw. Operating RPM is low enough. There’s plenty of time to fill.

It could be. Hard to say without small incremental changes. And once you go wide, it’s typically not very feasible to get it back narrow. There has been discussion before by some who think you should go wide before you go down with the floor and give up case pressure. If velocity suffers by going wide, it may very well be better to go with stock width and just add some duration.

To the latter part of your question, I don’t think intake velocity directly has much to do with transfer velocity or pushing out spent exhaust.

I’m in the wider rather than lower camp. I may have gone too low on this one. The plating forced me that way. Low intake and high transfers make lower case pressure and might effect transfer velocity.
But the piston displaces the same volume regardless. I don’t think anything I’ve done on that side made a huge change.

 

[Ketchup]

Right now, I think the problem was an oversight on my part. I came to it a few days ago, but only got to fixing it last night. @Dolkitafreak , you mentioned it, but at the time I didn’t know what you meant. I think this is why Echo went to the windowed piston. The 490 was killing transfer flow too early. A simple mod to the skirt seems more called for than full windowed piston, it would be interesting to run both in the same saw.


Haven’t run this yet, but I’m confident it will be an improvement. I’ve also been running an 8pin. Not sure if this little saw can handle that. More test cuts, then we’ll see about taking the transfers higher.

 

[farminkarman]

Right now, I think the problem was an oversight on my part. I came to it a few days ago, but only got to fixing it last night. @Dolkitafreak , you mentioned it, but at the time I didn’t know what you meant. I think this is why Echo went to the windowed piston. The 490 was killing transfer flow too early. A simple mod to the skirt seems more called for than full windowed piston, it would be interesting to run both in the same saw.
View attachment 365310

Haven’t run this yet, but I’m confident it will be an improvement. I’ve also been running an 8pin. Not sure if this little saw can handle that. More test cuts, then we’ll see about taking the transfers higher.

That is an area that I think most people miss. Good catch!

 

[Dolkitafreak]

Right now, I think the problem was an oversight on my part. I came to it a few days ago, but only got to fixing it last night. @Dolkitafreak , you mentioned it, but at the time I didn’t know what you meant. I think this is why Echo went to the windowed piston. The 490 was killing transfer flow too early. A simple mod to the skirt seems more called for than full windowed piston, it would be interesting to run both in the same saw.
View attachment 365310

Haven’t run this yet, but I’m confident it will be an improvement. I’ve also been running an 8pin. Not sure if this little saw can handle that. More test cuts, then we’ll see about taking the transfers higher.

Good stuff, we’ll see how it does. I think the 8 pin will be okay, about the same diameter as a 7 pin 3/8.

 

[Ford3000]

Will be interesting to see how it runs now with the piston mod,
lighter too.
More mix in, more to push up the transfers, should make a change
for the better.