thompsoncustom
ArboristSite Guru
any proof of this?
improved emissions is a great thing as long as it doesn't effect performance which it almost always does.
Stihl 2-mix strato vs Husky/Poulan strato
- Thread starter Old2stroke
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improved emissions is a great thing as long as it doesn't effect performance which it almost always does.
There’s a definite difference in hydrocarbon emissions. Previous generation 2 strokes purged the spent exhaust with 20–30% of the fresh incoming charge. Strato saws purge with fresh air.
KostasVolos
ArboristSite Operative
Doesn't that mean that more charge ( that 20-30% ) is left to cylinder after scavenging ?
And that more charge left to combust equals better performance ?
Isn't that turbochargers "push"
more charge ( through compressing it ) inside the cylinders of an engine ,in order to improve performance ?
What sort of engine does the 30% a case reed with two side transfers and one in the back aiming right at the exhaust?
They end up with similar amounts of charge still in the combustion chamber since the motor can only pump X amount of air in and out.
The 30% number is derived from the efficiency of strato saws over the previous generation. I’m sure that number varies. It could be 15% or it could be 40%.
Using the 372xtorq as an example, because it’s the closest model with strato tech compared to the previous generation 372xp, the xtorq is around 30% more efficient. There’s nothing else magical going on inside that would give it more efficiency. The transfer ports are fed from the same areas and the charge comes out in the same areas.
I would imagine reed saws operate at similar efficiency as any pre-strato saw. Incoming fuel is metered by the reeds rather than the intake skirt on the piston. I’m sure there are simple changes that happened along the way that made them more efficient, but not certain that had anything to do directly with the reeds.
Reed valve induction produced a more complete filling of the crankcase as they opened as soon as vacuum appeared in the crankcase and closed as soon as it was gone. No spit back through the carb. Most apparent at lower rpm (lugging speed) but at high rpm, probably the inertia of the incoming air/fuel charge did just as good a job of filling the crankcase in piston-port induction.
No, that's not what it means.
Most any traditional two strokes pukes that much or more fresh charge out the exhaust. Doesn't matter if it's reed or piston port.
Yea, pick up a 372 XTorque snd a OE372 and run them. It's pretty apparent the XT has more torque.
Torque is a measure of cylinder filling efficiency and strato saws are just more efficient in this regard.
Most likely from most of them being front fed and blowing the charge straight at the intake wall
thompsoncustom
ArboristSite Guru
so it's the difference in the transfer ports not the strato side.
Easy way to find if strato are better or worse for power is to see what the guys that port saws do most on average.
Do they 90% of the time end up running mixed charged through the strato port to make more power or do they try pushing more straight air. as running mixed air/fuel through the strato side is the only way to really test it.
Comparing saws with different ports is like comparing apples and oranges.
Little bit of everything. Transfers pointed hard to the intake helps torque.
The strato piston is inherently heavier by design, so naturally they don’t want to turn as high of rpm. So port timing is different than most to offset that, or make use of it.
If gutting the strato portion in the intake helps performance, the transfer area or timing has room for improvement
The strato piston is inherently heavier by design, so naturally they don’t want to turn as high of rpm. So port timing is different than most to offset that, or make use of it.
If gutting the strato portion in the intake helps performance, the transfer area or timing has room for improvement
I wouldn't assume that those long transfers would not work that well without the strato ports.
thompsoncustom
ArboristSite Guru
It would be interesting to see someone do a side by side comparison of the same model where they gutted the strato side and ported both saws to the exact same numbers, weighted the pistons, checked ignition timing, and everything you could to keep them as close as possible and see how it works out. Would also need a dyno tho to measure the results.
In the early days of strato saws alot of guys did gut the strato ports, but many don't now. What's that tell you?
thompsoncustom
ArboristSite Guru
that gutting the strato is always a improvement and is just emmissions garbage but maybe at this point the gains are just not enough to be worth the work.
I dont believe @huskihl guts them, but I bet he has tried both ways. Maybe he can go into that further.
He didn't gut mine, and I agreed with him that the only increase you would see is in fuel consumption.
Yeah, I don’t gut them. I have played around with it. I don’t want to get rid of the efficiency. But like I said in my post before that, if gutting the strato helps, it means that there is room for improvement in your transfer area or timing. Tree monkey did a thread on here a few years ago, and once he had ported a 462 to his timing numbers, he gutted the strato and it didn’t make any difference in cut times. Which is in line with my findings as well. It’s probably easier in most cases finding gains by gutting the strato which is why some guys do it.
