What is a "stratos" saw

[Tiewire]

I think I have a basic understanding of a two cycle engine, but what is a stratos engine?

[Saw Dr.]

It stands for stratified scavenging.  In short, the saw will have a two barrel (or split barrel) carburetor, and two distinct intake channels.  One channel carries only clean air while the other carries the fuel/air mix.  Each revolution, the clean air purges the combustion chamber and pushes the exhaust out before the fuel/air mix comes in.  This allows EPA compliance without any catalytic muffler or other emission devices.  As a side effect, they are incredibly efficient also.  They have been much maligned on the internet, as the first few of the type were incrementally heavier than the non strato design.  Most of that is gone now, and the current crop of stratos will HAND IT to pretty much all earlier designs in the performance department.  Stratified scavenging is good technology, and something you will want to have.

[Tiewire]

Thank You for "lifting the fog" on that for me.

[SawTroll]

It stands for stratified scavenging.  In short, the saw will have a two barrel (or split barrel) carburetor, and two distinct intake channels.  One channel carries only clean air while the other carries the fuel/air mix.  Each revolution, the clean air purges the combustion chamber and pushes the exhaust out before the fuel/air mix comes in.  This allows EPA compliance without any catalytic muffler or other emission devices.  As a side effect, they are incredibly efficient also.  They have been much maligned on the internet, as the first few of the type were incrementally heavier than the non strato design.  Most of that is gone now, and the current crop of stratos will HAND IT to pretty much all earlier designs in the performance department.  Stratified scavenging is good technology, and something you will want to have.

It is really only gone from the newer Husqvarna designs, the extra weight of the early strato saws pretty much still is present with the other brands.

[GregGA]

Hi all. I am new to chainsaws, having just purchased a NOS Redmax Gz4000.

It was made in July of 2006, before the acquisition by Husky.  Did not Redmax develop the strato charged 2 stroke?  I have a Redmax blower made in 2002 that is a strato.

When you say the first strato's weighed more, which makes other than Redmax had them before Husky bought the technology? Like I said, I'm new so if this is a well know answer, I apologize.

My GZ4000 weighs 9.1 pounds, while a non-strato Echo CS-400 weighs 10.1 pounds.  I am very happy with this saw, and only bought it because of my experience with the blower, and the help from CTYank on others over on AS.  To me, it seems very light and nimble.

I would be interested in knowing who else besides Husky and Redmax is using this technology.

Best regards,

Greg

[CTYank]

My understanding is that some of the EU powers-that-be arm-twisted Husqvarna to license strato technology to Stihl, so Stihl could remain competitive in the US market.

Reportedly Shindaiwa developed a similar scavenging scheme, thus tempting Echo to merge with them.

Earlier statement on how strato scavenging worked is incomplete/erroneous. Incoming pure air is back-filled into transfer ports while piston is near TDC, to be first-out when the transfers dump into the chamber much later in the cycle.

Funny how many transplants are here from AS. Been here a while myself, quite a while in fact.

Cheers from Yankee-land.

[Andyshine77]

My understanding is Redmax was in fact the first to develop the technology, and one reason Husqvarna bought Redmax.

http://youtu.be/IY7zQKw4qsQ

[Saw Dr.]

My understanding is that some of the EU powers-that-be arm-twisted Husqvarna to license strato technology to Stihl, so Stihl could remain competitive in the US market.

Reportedly Shindaiwa developed a similar scavenging scheme, thus tempting Echo to merge with them.

Earlier statement on how strato scavenging worked is incomplete/erroneous. Incoming pure air is back-filled into transfer ports while piston is near TDC, to be first-out when the transfers dump into the chamber much later in the cycle.

Funny how many transplants are here from AS. Been here a while myself, quite a while in fact.

Cheers from Yankee-land.

I thought the whole backfilling and TDC thing was an unnecessary complication.  He wanted to know how strato worked, and I gave a basic explanation.

[SawTroll]

My understanding is Redmax was in fact the first to develop the technology, and one reason Husqvarna bought Redmax.

Yes, but they bought Zenoah, not Redmax really. Redmax is just the marketing name of Zenoah products in the US (and maybe Canada as well?).

They apparently needed some patents that Zenoah controlled, to improve their own "strato" designs.
Remember that both Husky and Stihl made their own strato designs without access to those patents, and now Dolmar has done that as well - almost a decade later.

[SawTroll]

My understanding is that some of the EU powers-that-be arm-twisted Husqvarna to license strato technology to Stihl, so Stihl could remain competitive in the US market.

....

I believe that mainly was about the AT, but it may have been both.....