Mastermind Meets The Dolmar PS-6100

[Mastermind]

Thanks for that info Wolter. That is very interesting.

Neal it was blowing 195psi before porting. I cut the step out of the squish to get the squish clearance down, and therefore increase velocity. I also wanted to raise the exhaust a little without losing any compression.

Compression = volumetric efficiency. Dolmar's engineers evidently know that, their engines almost always test at 200psi or so stock.

 

[RedneckChainsawRepair]

Randy after watching all the videos here is what I took from them.

The 3 stock videos, 6100 run stock with no muffler mod or timing adjustments needed on stock saw. Seems like nothing really gained on just MM and timing adv in videos.

So either go stock or all the way with ported and other mods done. Is this how you see it?

 

[Mastermind]

That's the way I see it too K.

 

[Treespotter]

I have done a comparison on the test results of the KWF. This is the German test facility that tests forestry equipment.
Even without techno electronics the Dolly tech people found a way to make it more powerful and still use less fuel than competitors Stihl and Husqy.


Wolter

 

[Terry Syd]

Dolmar was very clever using the reeds in the strato function and created a strong work saw. The reeds allow the engine to breathe for a longer duration without a problem with blowback. The strong torque at lower revs appears to show two things, first the superior crankcase filling, and secondly, the reeds allow the crankcase to inhale through the reeds below peak delivery ratio so that there is less mixture drawn back down through the transfer ports.

If someone wanted to raise the point of peak power of the Dolmar, it appears that extra transfer time/area may be the ticket. The reeds would help prevent a serious drop in power below peak torque.

With 25 degrees of blowdown, it is not surprising that a MM mod would have less effect on the power. However, with a muffler mod there is less backpressure to worry about and raising the transfers begins to look like an option. Leave the exhaust stock and see how much extra transfer timing the engine can take before things start going backward. The old trick of nipping the edge off the side of the piston next to the transfers to increase the transfer timing could be a good way to find the 'sweet spot'. When a person has gone too far, then go back to the timing that worked, cut that in the jug and put in a new piston.

 

[bryanr2]

these saws for sure are getting my attention now. who is the resident dolmar dealer here?

 

[fastLeo151]

There hard to get I think were waiting on 6

 

[RedneckChainsawRepair]

these saws for sure are getting my attention now. who is the resident dolmar dealer here?

Couple dolmar dealers are sponsor here. I like cutting edge username 166. If choosing from NY. Ohio local is around $549 then tax. Can buy online $580 shipped to your door.

 

[fordf150]

I don't know what luck other dealers are having at getting them but it took me till first of January to get the last of four i ordered at the beginning of October. I ordered 4 more from other warehouses till couldn't find a warehouse with them in stock anymore. Now I am waiting on 6 more that were ordered in first part of January with 2 of those six already paid for and none on the shelf. Same with heated handle 5105's.

 

[sugarbush]

I don't know what luck other dealers are having at getting them but it took me till first of January to get the last of four i ordered at the beginning of October. I ordered 4 more from other warehouses till couldn't find a warehouse with them in stock anymore. Now I am waiting on 6 more that were ordered in first part of January with 2 of those six already paid for and none on the shelf. Same with heated handle 5105's.

you can get 5105 w/heated handles? no problem getting 6100's here in mn.

 

[fordf150]

Last I checked inventory central power, Atlantic power, and preferred power had zero 5105H, 6400H, 6100 in stock. I have all 3 if them ordered just waiting on them. I just started stocking heated handle 5105H and 6400H but underestimated the demand for them. MN is Magneto power? I am not able to see their inventory

 

[Chris-PA]

Dolmar was very clever using the reeds in the strato function and created a strong work saw. The reeds allow the engine to breathe for a longer duration without a problem with blowback. The strong torque at lower revs appears to show two things, first the superior crankcase filling, and secondly, the reeds allow the crankcase to inhale through the reeds below peak delivery ratio so that there is less mixture drawn back down through the transfer ports.

Reeds essentially make a variable duration intake port - but that has always been true of reed valve intake systems, yet the industry moved away from them due to other limitations. Here the reeds are on the strato intake, so the air-only inlet has variable timing - the duration of the air-only intake goes up with higher rpm, so the arrival of the fuel mixture will be delayed further at higher rpm (because the air volume in the transfers goes up). The mixture may well be leaned out some too. That is OK to some extent, as it counteracts the normal characteristic of the carb to get richer at higher rpm, but only in small amounts. Hence the small strato air valve and runners, and the conventionally sized carb.

That means this strato system is unable to provide much additional intake volume, unlike a piston-ported strato where the strato intake ports are often larger than the carb - the strato ports become the primary intake to the engine. So this design is just a conventional engine with a short duration intake and a small strato system tacked on. That it makes good torque is no surprise.

I believe Randy ported it by ignoring the strato system, which seems like the only choice. Having done that well the intake porting now flows better, the saws make more power and the strato function is further reduced. But I don't see anything very special in the reed ported strato system.

 

[SawTroll]

The reason I'm wondering is I believe the 562 had a 12.5mm carb. ........

As far as I know, there are two venturies there?

 

[Chris-PA]

As far as I know, there are two venturies there?

Two throttle plates, but only on carb & one venturi. The strato throttle plate controls just air, no fuel.

 

[SawTroll]

Two throttle plates, but only on carb & one venturi. The strato throttle plate controls just air, no fuel.

Obviously, but that air is part of the total resulting fuel to air mix in the cylinder, as far as I know.

 

[Chris-PA]

Obviously, but that air is part of the total resulting fuel to air mix in the cylinder, as far as I know.

Yes, which is what I was discussing in comment #212 above.

I think we just hit a language thing - you stated "As far as I know, there are two venturies there?", but the venturi is in the carb, so there is only one venturi but two throttle plates. I know what you meant.

 

[sugarbush]

Last I checked inventory central power, Atlantic power, and preferred power had zero 5105H, 6400H, 6100 in stock. I have all 3 if them ordered just waiting on them. I just started stocking heated handle 5105H and 6400H but underestimated the demand for them. MN is Magneto power? I am not able to see their inventory

surprised 5105h and 6400h would come up as able to order, show discontinued here for quite awhile---- yes magneto power here. there is some old stock 6400h saws in the Wisconsin warehouse.

 

[fordf150]

surprised 5105h and 6400h would come up as able to order, show discontinued here for quite awhile---- yes magneto power here. there is some old stock 6400h saws in the Wisconsin warehouse.

I can get them.. didn't say it was easy or quick. I can order from magneto but cant check stock and ordering anything from them is expensive. 6100 from them to my shop was $550. Magneto isn't a team player.

 

[Terry Syd]

Chris, there is too much to address in your post. I think this is a case where the proof will be in the pudding. There was one statement "and the conventionally sized carb" which may need to be clarified. I don't remember the size of the carb being stated. A conventional saw of this size would commonly be using a 17mm venturi, but I don't know if that is true in this case.

Randy said it is much bigger than the 562 carb, but didn't quantify it. Perhaps someone with a 6100 could tell us what kind of carb (C3M?) it is running and what size venturi. There is a possibility that a smaller carb (less flow) was used on the saw to bias the system towards more strato air at high rpm. If so, that may open up the possibility of more top end by having a larger carb.

 

[Chris-PA]

A conventional saw of this size would commonly be using a 17mm venturi, but I don't know if that is true in this case.

Yeah, I'd like to know the carb size too.