Mastermind Meets The Dolmar PS-6100

[Chris-PA]

There does not appear to be much opening area between the transfers and the case - just a pretty narrow slot?

 

[Chris-PA]

OK, so the strato pathway is controlled exclusively by a shared linkage with the throttle, and the reed valves keep the port closed the rest of the time? The when the strato path is open, the air is sucked into the upper transfers and mixes with the "mix" coming up thru the case via the lower transfers? Is my brain on track with this? Thanks

Pretty much, but the mixing doesn't really happen until later when the fuel/air mix makes it up into the cylinder from the case. So air gets pulled in through the reed valve into the transfer runners on the way down to the case, and then flow reverses and it is pushed back up into the cylinder. Meanwhile, air has been pulled through the carb and into the case, and it gets up to the cylinder later.

 

[HuskStihl]

Pretty much, but the mixing doesn't really happen until later when the fuel/air mix makes it up into the cylinder from the case. So air gets pulled in through the reed valve into the transfer runners on the way down to the case, and then flow reverses and it is pushed back up into the cylinder. Meanwhile, air has been pulled through the carb and into the case, and it gets up to the cylinder later.

So does the "clean air charge" hit the combustion chamber before the mix to push exhaust gasses out, or after to complete the burn on the downstroke?

 

[Chris-PA]

So does the "clean air charge" hit the combustion chamber before the mix to push exhaust gasses out, or after to complete the burn on the downstroke?

The clean air gets there first, pushing the exhaust out. The rich fuel charge gets there late to prevent it from getting out the open exhaust port, but hopefully with enough time to mix thoroughly with the air already there. It's not supposed to be stratified at combustion, only on the way to the cylinder.

That is true for all stratos, but this one uses a reed valve on the air intake rather than a piston port. That means the strato port duration does not need to be symmetrical about TDC - it closes as soon as the pressure in the case rises which will likely be before the regular intake closes.

The case can begin to pressurize as soon as the intake closes, which will be sooner with this setup because it does not have to wait for a long duration strato port to close. So it should develop good transfer velocity. But reed valves have their own limitations, and I'm really curious how this works in practice.

 

[HuskStihl]

Thank you very much for the explanation. I appreciate u'r taking the time!

 

[Treespotter]

now I'm gonna put it back together and run it with just muffler work.

I may play with this one a bit.

I've been playing around with it for a while now. And do you know what? I'm an arborist for thirty years now and this is the first saw that puts a smile on my face every time I get it out of the van. It's a hassle free saw that sometimes stalled when idleing the first 5 tanks of fuel. I hesitated pulling a screwdriver out to retune it but could prevent myself doing it. The stalling stopped and the saw runs great. I love it.


Wolter

 

[7sleeper]

Been waiting a long time for this thread!

7

 

[Mastermind]

I reassembled it today. Videoed it stock, then muffler modded, and then with the timing advanced. Jon and I are gonna top and piece down a large hickory that is in a spot that just dropping it ain't possible. I'll take this saw and put some more fuel thru it.....

 

[bryanr2]

opcorn: just something to do.

 

[Plan-b]

Kawasaki uses reeds on the strato side in the tj27e engine, I think they started doing this around 2010.

Randy, are you finding it cold blooded as other stratos?

 

[SawTroll]

Reed-valved stratos are cool n' stuff, but did you guys check out the awesome stamped chain direction indicator???!!! God how I wish all my saws had that!

It may of course mainly be a way to "work around" someone elses patents?

 

[Trx250r180]

seems like in the old days a thread like this would be on page 9 or 10 by now ........

 

[fordf150]

Its on page 9 elsewhere

 

[HuskStihl]

seems like in the old days a thread like this would be on page 9 or 10 by now ........

If it were a MS290 farm boss, it would be on 15 by now

 

[tallguys]

It may of course mainly be a way to "work around" someone elses patents?

A patent on chain direction? Just kidding.

 

[Como]

I like the look of it, would match my Makita. Next size up.

Probably not many in my situation.

 

[Chris-PA]

So this saw effectively has a hybrid reed valve/piston ported intake system. I'm not really sure what the advantage of that would be. The reed strato intake may open sooner and close sooner, but the ported intake is still symmetrical about TDC and held open. On the other hand with that big angle between the intake closing and the transfers opening, combined with a small case volume, the piston will be fighting against the case pressure for almost 1/3 of the down stroke - the energy going into compressing the case is not going out of the crankshaft.

I dunno, I'm just a noob when it comes to this stuff but I'm not seeing the big advantage. Heck, if you count the reed valve as a moving part then has more moving parts than a piston ported strato.

 

[Axlerod74]

No left over room in the crankcase for anything.............

 

[mtlogdog]

i like the look of the saw not as good lookn as 6400-7900 but still pretty

 

[jimmycrackcorn]

Those stamping on those reeds look like Moto Tassinari. I put them in all my bikes & sleds. Their the best you can get, they definitely increases throttle response over the brittle stock ones. They also compliment intakes & exhausts. If those are them, it's good to see they didn't cheap out on inferior ones.

I know bikes & saws are two different animals but know that I look @the pics again, I'm having a hard time understanding how these reeds are incorporated into the intake. I also don't understand strato engines 100% & that could be the reason. TO ME, it looks like the reeds will only handle the air, unless the unit stacked on top of the carb handles fuel as well. Funny thing is, I tried to Google how this setup works so I wouldn't sound like an a$$ (too late) & this Mastermind thread is the only search result with info.. Nothing from Dolmar, nothing anywhere else.

I'm curious to see how this works out, keep up the good work Randy.