Mastermind Meets The Dolmar PS-6100

[Mastermind]

The chain is a new loop of Oregon LGX

 

[mweba]

The chain is a new loop of Oregon LGX

Oregon sells chain dull these days? Lotta dust out da back.

Maybe it's rotten? Ya, that's it...rotten wood.

On the other hand. It could be seasoned hard wood...

Hell if I know.

 

[jimmycrackcorn]

So the reeds don't handle fuel..? Anyone?

 

[Mastermind]

Just air Jimmy.

 

[fordf150]

So the reeds don't handle fuel..? Anyone?

Reeds are just on the strato so no fuel through them

 

[jimmycrackcorn]

Just air Jimmy.

Reeds are just on the strato so no fuel through them

Thanks my dudes.. I understand it now, at least the intake aspect that is.. Y'all ever seen them used like that? I haven't.. But I've also been out of the power sports loop for a bit.

 

[Mastermind]

This is a new animal for me.

That oak is some two year old stuff that's pretty damn gnarly. I'll get a better piece before round two.....

 

[CTYank]

Reportedly RedMax Stage 1 stratified scavenging used reed valves similarly. They did invent "strato" 2-strokes. So, this approach is certainly pretty main-stream stuff, with some history. Who knows how much was shared/licensed?
I was already interested in this saw some time back. Sorry, Troll.

 

[procarbine2k1]

Watching closely! I am happy to see Dolmar pumping out new saws. I would love to see more Dolmar dealers popping up, I figured more mom and pop shops would be looking into Dolmar that weren't happy with the whole Jonsered/Tilton thing, or ones that wanted to add to the OPE brands they already offered.

 

[HuskStihl]

The imbedded youtube videos blur the fast stuff so much the discharge always tends to look dusty to me. On my phone I can see a stream of big chips, on YouTube looks like a cloud of dust

 

[mweba]

The imbedded youtube videos blur the fast stuff so much the discharge always tends to look dusty to me. On my phone I can see a stream of big chips, on YouTube looks like a cloud of dust

This man gets it.

 

[Terry Syd]

Its been a while since I looked at the patents, but I recall the first strato design was a reed valve to the upper transfers. That design did not have a control valve to bring in the strato later, it operated all the time, even at idle.

Some of the Dolmar design may be an attempt to get around other patents.

The first thing I noticed when I saw the two intakes was how small the strato butterfly was in comparison to the carb. Perhaps the reeds allow the strato port to remain open much longer and the extra area of the ports isn't needed. Reeds tend to stay open much longer than you would think they should.

This is an interesting design, it kinda reminds me of the motorcycle engines that used a piston port design that had a 'floor' to the port that fed a reed valve. That design gave the engine more mid-range torque.

EDIT: I also noticed the transfer duration, from your figures it would be just 100 degrees. Also from the pictures it looks like the transfer ports may have emphasised a wider port to bring the time/area back up.

 

[Chris-PA]

EDIT: I also noticed the transfer duration, from your figures it would be just 100 degrees. Also from the pictures it looks like the transfer ports may have emphasised a wider port to bring the time/area back up.

Also interesting is that the "blowdown" is fairly large, whereas with other stratos I've seen that angle is smaller than typical. Definitely some different stuff going on here.

 

[mweba]

Its been a while since I looked at the patents, but I recall the first strato design was a reed valve to the upper transfers. That design did not have a control valve to bring in the strato later, it operated all the time, even at idle.

Some of the Dolmar design may be an attempt to get around other patents.

The first thing I noticed when I saw the two intakes was how small the strato butterfly was in comparison to the carb. Perhaps the reeds allow the strato port to remain open much longer and the extra area of the ports isn't needed. Reeds tend to stay open much longer than you would think they should.

This is an interesting design, it kinda reminds me of the motorcycle engines that used a piston port design that had a 'floor' to the port that fed a reed valve. That design gave the engine more mid-range torque.

EDIT: I also noticed the transfer duration, from your figures it would be just 100 degrees. Also from the pictures it looks like the transfer ports may have emphasised a wider port to bring the time/area back up.

I'm lazy sooo. I'll quote my thoughts on the port/reed timing design.

"I would assume the same applies for muffler and scavenge as any saw. Seams to me, the strato is drawn from bdc until the upper trans are closed off by the piston. Once that occurs, a fresh charge is on top when the intake opens at 71°. If my assumption is correct, the only real difference is the path of the strato charge. Doesn't travel through the piston as we are use to."

"The only time I can logically see a pressure below atmospheric in the upper trans is described in my previous post. . Now the standard strato uses a side piston port that open the same time of the intake. This draws low pressure through both at the same time but strato has less time open."

Digging this design as it makes changes to the flow pattern easier to manage than the typical Strato design.

 

[mweba]

Also interesting is that the "blowdown" is fairly large, whereas with other stratos I've seen that angle is smaller than typical. Definitely some different stuff going on here.

I would assume the blow down is greater on this saw as the duration allowed for fresh air in the upper trans is much less than the typical design that opens starto and case volume at the same time.


Meaning less "clean" air needs to scavenge out.

 

[Chris-PA]

I would assume the blow down is greater on this saw as the duration allowed for fresh air in the upper trans is much less than the typical design that opens starto and case volume at the same time.


Meaning less "clean" air needs to scavenge out.

Well, increasing that angle is one of the techniques used on a non-strato engine to reduce scavenging losses (reducing the time both ports are open). Everything tells me that the strato function on this saw is just less effective than piston ported strato systems - the little air valve and small looking strato runners, the bigger carb, the larger blowdown angle - at least from the point of view of reduced scavenging losses. The question is whether it has other advantages? If the strato system works well enough to meet the limits and it makes more power, well then good. But does it?

Also, the GZ4000 has a longer duration on the strato intake than on the regular intake, while numbers from others I've seen have the strato duration shorter. I have one with a strato duration of 163 and an intake of 144, and that runs quite nicely.

 

[Terry Syd]

Seams to me, the strato is drawn from bdc until the upper trans are closed off by the piston. Once that occurs, a fresh charge is on top when the intake opens at 71°.
.

At BDC the transfers will still be flowing because of crankcase compression. However, once the transfers are closed, the crankcase can begin to create a low pressure to draw in the next charge. In the case of a straight piston port engine, there is a lag time between the transfers closing and the intake opening (say at 80 degrees BTDC). With the reeds, there will be no lag in induction, the reeds will begin to flow as soon as the pressure drops. There is also less pumping loss when the engine can actually breathe rather that fighting against an increasing low pressure below the piston.

The elimination of that lag time in the induction cycle is what gives a rotary valve engine such an advantage. A reed valve engine also has that advantage, unfortunately it also has the reeds obstructing the flow.

I do like this design, it appears to have some potential.

 

[Chris-PA]

There is also less pumping loss when the engine can actually breathe rather that fighting against an increasing low pressure below the piston.

But doesn't it have to fight high pressure the way back down for a longer time, due to the reed closing sooner? The piston ported intake is still open, but that is a short duration.

 

[mweba]

At BDC the transfers will still be flowing because of crankcase compression. However, once the transfers are closed, the crankcase can begin to create a low pressure to draw in the next charge. In the case of a straight piston port engine, there is a lag time between the transfers closing and the intake opening (say at 80 degrees BTDC). With the reeds, there will be no lag in induction, the reeds will begin to flow as soon as the pressure drops. There is also less pumping loss when the engine can actually breathe rather that fighting against an increasing low pressure below the piston.

The elimination of that lag time in the induction cycle is what gives a rotary valve engine such an advantage. A reed valve engine also has that advantage, unfortunately it also has the reeds obstructing the flow.

I do like this design, it appears to have some potential.

Did you read what I wrote?

At bdc the pressure is atmospheric and not flowing. The strato draws from bdc until trans close. At which point the case is filled.

 

[Mastermind]

You fellers think too much.

I'm gonna go play some chess....