Stock Strato Port Timing Numbers

[Chris-PA]

I was curious if others had measured the stock port timing on various strato engines. I measured a GZ4000 and got:

E = 132
I = 137
I(S) = 165
T = 103

So it looks like they used a short exhaust duration short to keep combustion pressure up, run a very small angle between exhaust opening and transfers opening ("blowdown" = 15deg) because it's mostly just air lost to scavenging, and a long combined intake duration. The strato intake ports open quite a bit before the main intake, but it is pulling air down through them and into the case, so it would seem they should count as intake duration.

The strategy seems to work very well, producing quite a lot of power for a 40cc saw. I'm wondering if other strato saws use the same approach?

 

[one.man.band]

576xp
durations

exh.: 154
int.: 128
trans.: 120
bd: 17
air: weird one here, not symmetrical opens 310, closes 75 = 125
measured from top of piston pocket on up direction, bottom of piston pocket on down stroke. for this motor anyway, the air and trans ports dont line up. maybe we measured in different ways, donno.

was thinking it had more of a transfer effect.

-omb

 

[Chris-PA]

Here is what I measured (had a hard time getting a good picture) - the strato piston slot has just opened in the front (left) transfer port (piston moving up), allowing air to move from the air valve, across the piston and down through the transfers into the case.

I can't see how a port opening could be asymmetrical (with respect to TDC or BDC) in a piston ported engine, but I have not looked at one of those.

 

[one.man.band]

the piston pockets on the 576 looks similar to this 562:

don't have a photo.

moodys build on the 562 has some good pics of the piston.
http://www.arboristsite.com/community/threads/a-look-at-how-i-do-a-562xp.247543/

on the upstroke, the top edge of the piston pocket recess controls where it opens. same as yours. i added 25 degrees (height of the piston pocket recess) on the downstroke, because, (the way i see it anyway), the bottom of the piston pocket recess controls where its opening. hope that makes sense.

the other recess above the "air piston pocket" is (are lightening holes) to reduce weight of piston. on this piston anyway.

-joe

EDIT: worth mentioning that on the 576.....the flow of the "air" goes into the bottom "air pocket".....then through the wrist pin....out to the other side of the piston...and into that air pocket......where its exposed to air. vice versa for that matter.

interesting to say the least.


-joe

 

[Chris-PA]

The GZ4000 is different and simpler (this thing ate a small end bearing so there are some added "features" in there!):

 

[one.man.band]

on the husq, wonder if the fresh air has a cooling effect on the small end bearings? on it the pocket extends closer to the wrist pin.

its design is different from the pocket in gz4000, which has some meat between the pocket and the pin. maybe the husq technology is licensed, ST would have a handle on those matters.

-joe

 

[Chris-PA]

I have to believe the design is evolving too. The picture I showed is actually from a GZ4000 clone made by Jenn Feng in Taiwan, and the oldest one of these I have is from 2004. The Zenoah parts look exactly the same. So it is a bit earlier than these Husky designs.

The other side of it is that it looks like quite the puzzle trying to fit all the ports and transfer slots in so they don't interfere with each other, and they may have just decided to go through the wrist pin area because they needed the space. That makes the pin shorter though - but not that different than other pistons with cutouts.

 

[one.man.band]

chris...

got thinking about the "air" through the wrist pin thing, (this time, without a beer in hand), did not think of the fact that the "air" port on the other side of the motor, would push some air in the opposite direction, through the pin. in effect, the two "air" ports on opposite sides of the motor would cancel eachother out. so really, the air would just collide from both sides within the pin. does that make sense?

way better than cats!

regards,
-joe

 

[Chris-PA]

I don't believe any of the pins I've played with have been drilled all the way through? Are these hollow?