Discussion Starter

[Wonkydonkey]

My question is……What does the 2stroke tuners hand book say about it

 

[redline4]

Might be the curve of the port at the cylinder wall. Hard to see in 2D.

That must be it.

 

[jacob j.]

There was a local builder here who was angling his upper transfers in a similar fashion, and there's one for sure in Idaho currently doing it.

Are any of the OPE builders dressing their upper transfers in this way?

 

[Mastermind]

Thanks for sharing Randy....a couple things stand out when looking at this cylinder.

1) Staggered opening of the transfers with the intake side opening first. - would tend to help lift the charge upward
2) Upper transfer roof angle seems to point upward quite a bit - also would would push the charge upward
3) upper transfer height relative to the exhaust seems kinda low suggesting a good amount of blowdown...maybe it isn't as I'm not used to looking at a cylinder like this.
4) tapered squish band most likely employed to help push the charge upward toward the spark plug in the chamber

All this seems to point toward trying to make the engine produce power at a higher RPM vs. being a torque monster....at least that is how I would interpret what I am seeing.

I'm kinda surprised at the cross section of the intake port....near the boot it looks huge!

Kinda cool seeing it this way huh?

 

[srcarr52]

There was a local builder here who was angling his upper transfers in a similar fashion, and there's one for sure in Idaho currently doing it.

Are any of the OPE builders dressing their upper transfers in this way?

No, I've had the best luck with the exact opposite.

 

[farminkarman]

There was a local builder here who was angling his upper transfers in a similar fashion, and there's one for sure in Idaho currently doing it.

Are any of the OPE builders dressing their upper transfers in this way?

Opening the intake side of the upper transfers first doesn’t make sense to me. On the other hand, making the transfer roof blow upward can certainly help pick up some rpm, but at the expense of some low end grunt.

 

[sawmikaze]

I thought maybe the angle of the transfer made it cut downhill better.

Got me.

 

[Mastermind]

I thought maybe the angle of the transfer made it cut downhill better.

Got me.

Seems logical Kenny.

 

[Ketchup]

Aren’t 500i and 661 transfers sloped upward toward the intake?

 

[Mastermind]

Aren’t 500i and 661 transfers sloped upward toward the intake?

No. 661 is high on each end, and lower in the middle. 500i is highest on the exhaust side.

 

[Moparmyway]

500i

 

[HYPERSAWS]

Looks like they are trying for good scavenging and a little more rpm

 

[CR888]

Well the duration of the transfer opening gets extended with an angled port, perhaps also controls the charge entering chamber in a more orderly fashion. Nice job of slicing the cylinder, so this is quite a way into the 066/660 series being an early MS660. I imagine many designs and changes were made in this series.

 

[huskihl]

Every 2 port stihl I’ve seen opened intake side first. I figured they were giving the exhaust more time to get out before opening that side of the transfer port

 

[farminkarman]

Every 2 port stihl I’ve seen opened intake side first. I figured they were giving the exhaust more time to get out before opening that side of the transfer port

Perhaps an emissions or fuel economy thing?

 

[Funky sawman]

There was a local builder here who was angling his upper transfers in a similar fashion, and there's one for sure in Idaho currently doing it.

Are any of the OPE builders dressing their upper transfers in this way?

I know Dean at Washington hot saws did that style of transfer ports on my 372xpg. I think Jason Egan is doing it too if I recall

 

[huskihl]

Perhaps an emissions or fuel economy thing?

Yeah, my thoughts were along those lines. Emissions

 

[huskihl]

Perhaps an emissions or fuel economy thing?

It could also be because doing it that way tends to make them a little bit higher strung in my experience. Maybe that’s what they were after

 

[Duane(Pa)]

I really envy you guys that “get” this sh!t. @drf256

 

[pbillyi69]

I really envy you guys that “get” this sh!t. @drf256

i know what you mean. i look at the picture and think the intake is on the right. right? lol