Thread: Does the "strato" design reduce lifespan..?

When the strato first hit the market (Husky 455), it was predicted to have a short engine life due the lean running characteristic of that design. However, several other models & brands have this design. I haven't read or heard about lean running failures, scorched pistons, etc. So is the strato really leaner or does this scavenging affect the combustion temp/pressure significantly?

The 'Strato' or 'X Torq' design is a stratified charge into the cylinder. Take a look at a cut away diagram of the cylinder and you will see how fresh air (no fuel) is fed into the top part of the transfers. It is this part of the charge that is 'lean' (like real lean).

That part of the charge is the first part of the charge into the cylinder. As it loops around scavenging the cylinder it begins to exit out the exhaust port, pushing the exhaust gases with it. The charge behind it contains the fuel mixture for the cylinder. When the exhaust port closes that fuel mixture gets trapped in the cylinder.

I am still running in my 450 and the plug is showing a 'rich' mixture. After another couple of tanks of fuel through it, I will lean it out a bit. The fuel mixture screw controls the mixture just like a conventional two-stroke.

The fact that the Strato design uses less fuel is not because the mixture is lean, it is because there is no (or less) fuel mixture that escapes out the exhaust port.

do the top part of the transfer get the air from someplace other than the carb?

I doubt if it would. There has been plenty of testing and the strato engines have been out in the field for a while now. If I understand the process correctly, it isn't really designed to lean the fuel-air mix out, but to have a puff of air (with no fuel mix) as the last little gasp that follows the spent charge out the exhaust port.

Older two stroke designs allowed an alarming portion of the fresh charge to slide right on out. This wasn't too cool for the air, but even more importantly, it was pretty hard to get any work out of it. I would suggest the strato charge thing is a huge gain for a few applications where a little more work from the gas is a great thing. Imagine where we might be with two-stoke bikes if we'd had smokeless oils and strato engines 30 years ago.

A close friend had a Suzuki 750 water-cooled two-stroke he called the water buffalo. Sucked on gas mileage, smoked like a chimney, and wasn't all that great a performer.

Evan, here's a thread with an explanation and diagram -

what is "strato charged"

In my opinion the only thing that is going to reduce lifespan is that you have a few more points of failure on a strato saw then a conventional, the air burps in the charge stream shouldn't have any siginifcant effect on jug or piston longevity.

the strato engine is a solid design, only draw back is the weight. I work on both the husky and stihl saws and both have proven track records.

It's generally the lean carb settings and constricted exhaust coupled with heavy use that contributes to strato burning up. The fresh air charge is actually brilliant. IMO

Originally Posted by kevlar

the strato engine is a solid design, only draw back is the weight. I work on both the husky and stihl saws and both have proven track records.

Nice power too! The strato is not the DOOM of the chainsaw world IMO!

i was always amazed how much wood i could cut on one take with the 455.

The only strato saw I worked on was a 455 and it looked like it had two carbs stacked the top one was just a butterfly that fed air to the upper transfers and opened as the throttle opened the lower one was just like a normal carb.

Originally Posted by ironman_gq

The only strato saw I worked on was a 455 and it looked like it had two carbs stacked the top one was just a butterfly that fed air to the upper transfers and opened as the throttle opened the lower one was just like a normal carb.

What was your general impression of the saw? Did it seem more time consuming to repair? I've seen a few pistons on Ebay and they look strange!

Originally Posted by outdoortype

What was your general impression of the saw? Did it seem more time consuming to repair? I've seen a few pistons on Ebay and they look strange!

At first glance, they look like something you don't want to mess with. In reality, after you do a few there isn't much difference. Two extra carb screws is not a big deal.

Okay strato saw users - are the strato's really much better on fuel consumption???
Can you notice the difference?

They are way better. My buddies 455 uses a lot less gas than even my 361 which I didnt think was too hard on fuel