Question about Crank Stuffers Case Volume and Primary Compression

[edisto]

Strato's blow fresh air, so they are the most efficient at fuel to power, ie not wasting fuel, not total power, ie fuel used for combustion.

Even in a 4-stroke the amount of residual exhaust gas is a component of total power.

A traditional two stroke does this well over a pretty narrow band compared to a strato charged engine. And torque is a measure of cylinder filling efficiency of fresh charge.

Thanks for that! I couldn't get my head around why the strato designs do a better overall job of scavenging, but having an efficiency that is less sensitive to rpm makes perfect sense.

 

[srcarr52]

I've watched a lot of dyno video's. Has anybody made more power with 70cc's without a pipe than the oe 372xp at this time? Please correct me if I'm wrong(with links to video's, not opinions). I would think the definition of the most effecient scavenging would equal the most air fuel in the cylinder and then the most power. If so I would argue that it has the most efficient scavenging without stuffers of any saw. Strato's blow fresh air, so they are the most efficient at fuel to power, ie not wasting fuel, not total power, ie fuel used for combustion. I accept that a lot more development has gone into that platform over the years than any other and could skew results.

I've made more from a 572 than most get from a 372. That was with a gutted muffler but breathing through the stock spart screen.

 

[Outback]

Nice, I stand corrected.

 

[bwalker]

I've made more from a 572 than most get from a 372. That was with a gutted muffler but breathing through the stock spart screen.

I believe Ed Heard has said he gets more out of a 372XT than a 372 OE.

 

[Mastermind]

I believe Ed Heard has said he gets more out of a 372XT than a 372 OE.

More torque for sure.

 

[bwalker]

More torque for sure.

You know it's like anything else. When something new comes out there is a learning curve associated with it. I think enough guys have ported strato saws now that they have a good handle on making them perk.

 

[Mastermind]

You know it's like anything else. When something new comes out there is a learning curve associated with it. I think enough guys have ported strato saws now that they have a good handle on making them perk.

It's all about port timing. Like all other saws....but different.

 

[sawmikaze]

I believe Ed Heard has said he gets more out of a 372XT than a 372 OE.

I always said the XT had more ass than the OE.

The CCC never wanted to hear it.

 

[sawmikaze]

I've made more from a 572 than most get from a 372. That was with a gutted muffler but breathing through the stock spart screen.

I'd love to see the difference with and without a screen...

 

[bwalker]

I always said the XT had more ass than the OE.

The CCC never wanted to hear it.

CCC?

 

[sawmikaze]

CCC?

Cookie Cutters Club

 

[edisto]

It's all about port timing. Like all other saws....but different.

I'm not looking for national secrets, but would you be willing to share any generalities? A long while back I followed an early attempt to port a strato that wound up with giving up and hogging out the entire intake. It seemed to me at the time that there should be a way to take advantage of the strato design instead of tossing it away, but I couldn't get my head around how one would go about it.

 

[Mastermind]

I'm not looking for national secrets, but would you be willing to share any generalities? A long while back I followed an early attempt to port a strato that wound up with giving up and hogging out the entire intake. It seemed to me at the time that there should be a way to take advantage of the strato design instead of tossing it away, but I couldn't get my head around how one would go about it.

By shortening the blowdown you can make good gains on a lot of these strato engines. The 562 was an eye opener. About 11 degrees. When looking at many others, you begin to see that they have much longer blowdown time, and much less power.

 

[srcarr52]

I'd love to see the difference with and without a screen...

I would pick up some. My 550 gained .3hp with a larger muffler mod.

 

[sawmikaze]

I would pick up some. My 550 gained .3hp with a larger muffler mod.

Did you test it with and without a screen ?

 

[bwalker]

I'm not looking for national secrets, but would you be willing to share any generalities? A long while back I followed an early attempt to port a strato that wound up with giving up and hogging out the entire intake. It seemed to me at the time that there should be a way to take advantage of the strato design instead of tossing it away, but I couldn't get my head around how one would go about it.

It's funny. Anytime something new in the chainsaw world comes out you have half assed porters saying things like "doesn't take to porting". You seen this with the Dolmar 7900,550xp, strato charged saws and many others.
What's really going on is these morons never understood a two stroke in the first place and only made a semi acceptable saw was either by trial and error or stealing others numbers. There are a couple guys that were on AS I am thinking off..
In addition hogging out the intake on a piston ported 2 stroke almost never goes well...

 

[edisto]

By shortening the blowdown you can make good gains on a lot of these strato engines. The 562 was an eye opener. About 11 degrees. When looking at many others, you begin to see that they have much longer blowdown time, and much less power.

I appreciate it! Now I just have to spend some time wrapping my head around the "why" part.

It seems like the additional inlet for air would allow for better filling of the lower transfers/crankcase. Does that result in overall higher crankcase pressure on the down stroke that can be taken advantage of?

It's funny. Anytime something new in the chainsaw world comes out you have half assed porters saying things like "doesn't take to porting". You seen this with the Dolmar 7900,550xp, strato charged saws and many others.

That never made sense to me either...engineering is always about balancing performance with cost, and now balancing both with emissions regulations. "Doesn't take to porting" would mean a design that couldn't be improved upon in terms of performance, which just can't exist in a mass-produced saw.

 

[Mastermind]

It seems like the additional inlet for air would allow for better filling of the lower transfers/crankcase. Does that result in overall higher crankcase pressure on the down stroke that can be taken advantage of?

It sorta speeds up the purge process. More fuel rich mixture ends up in the muffler, but it allows a longer fill time...assuming the exhaust ain't too high.

 

[srcarr52]

Did you test it with and without a screen ?

No. It was a different muffler.