Popup vs Flat Top?

[opinion]

Like I said yesterday......I'm gonna try to leave the fussing about this stuff at the door when I check in here.

To be honest (and as everyone already knows) it's got far less to do with saws than it has to do with bad blood from days gone by. I'm bad to dwell on stuff.....and I never, ever let go of a resentment. Cross me today, and you have a enemy from now on. That's not healthy maybe, but it's true. That's likely the biggest issue here. I will try to let this go........I'm even sick of reading this crap.

You should have a boxing match for 3 minutes. Let it all out and maybe you can put it behind and have a beer.

 

[angelo c]

Big Group Hug !!!

C'mon now everybody in close for the family shot !!!!

SMILE !!!!!


poof

 

[angelo c]

Hey, this is cool! I'm a johnny come lately, how long till I start having a fight with one of these other builders?

you need to be a "sponsor" first...with "skin in the game" you have rights to equality !!!!

 

[angelo c]

now those are some BOOBS !!!!


SOOOOO HAWTTTTT !!!!

Rep sent Jeremy !!!

 

[RiverRat2]

cool but he might catch something he didn't want on his hook.

Torque is way more important than, "power."

 

[David Young]

I have not seen a direct mention of a couple of things i think are important and come in play.
one is laminar flow

either a flat or smooth dome will facilitate laminar flow over the crown.

laminar flow is the opposite of the turbulence right? so why would that be good?

you want maximum flow without disruption until the two transfer streams collide and will naturally head up the back of the cylinder wall setting up the loop scavenging.

during this filling of the cylinder with fresh mix any remaining burnt gasses that are not swept out will be trapped and dilute the next charge.

in theory we want 100% fresh charge in the cylinder for compression. we are trying to increase performance in many ways by attempting to increase efficiency by 2 percent here 4 percent there. Throw it out the window if your cylinder only has a 85% charge in it.

when the transfer streams hit the pop up what do you think happens? they go up right, its essentially a little ramp. when that happens the flat portion of the popup will have burnt gases sitting on top of the crown. That will be mixed in the next cylinder charge yes you have increased compression which makes this charge more efficient but it is a smaller charge.

I do think if a popup was gradual enough or small enough it could work but I think the squish cut is the better choice.

I think the real benefit of the cut squish is scavenging efficiency.


a popup has typically shown a performance increase compared to a saw that just has the squish set and not cut.

but what if we put a bigger charge that is more pure in the motor with lower compression?

David

 

[Mastermind]

Nice post David.

Well thought out, and well written.

I don't really have a good education, and I have trouble putting into words what I've seen and studied. I wish I was better able to put it out there.

 

[sunfish]

I have not seen a direct mention of a couple of things i think are important and come in play.
one is laminar flow

either a flat or smooth dome will facilitate laminar flow over the crown.

laminar flow is the opposite of the turbulence right? so why would that be good?

you want maximum flow without disruption until the two transfer streams collide and will naturally head up the back of the cylinder wall setting up the loop scavenging.

during this filling of the cylinder with fresh mix any remaining burnt gasses that are not swept out will be trapped and dilute the next charge.

in theory we want 100% fresh charge in the cylinder for compression. we are trying to increase performance in many ways by attempting to increase efficiency by 2 percent here 4 percent there. Throw it out the window if your cylinder only has a 85% charge in it.

when the transfer streams hit the pop up what do you think happens? they go up right, its essentially a little ramp. when that happens the flat portion of the popup will have burnt gases sitting on top of the crown. That will be mixed in the next cylinder charge yes you have increased compression which makes this charge more efficient but it is a smaller charge.

I do think if a popup was gradual enough or small enough it could work but I think the squish cut is the better choice.

I think the real benefit of the cut squish is scavenging efficiency.


a popup has typically shown a performance increase compared to a saw that just has the squish set and not cut.

but what if we put a bigger charge that is more pure in the motor with lower compression?

David

Almost too long to read, but I did read it and you make some very good points there!

 

[Mastermind]

Yes he does.......that post probably makes more sense than anything I've read on the subject.

 

[David Young]

Thanks guys

now im going back to being a smart a55

 

[sunfish]

Yes he does.......that post probably makes more sense than anything I've read on the subject.

Yes, makes lot of sense and very easy to read!

 

[cuttinties]

I have not seen a direct mention of a couple of things i think are important and come in play.
one is laminar flow

either a flat or smooth dome will facilitate laminar flow over the crown.

laminar flow is the opposite of the turbulence right? so why would that be good?

you want maximum flow without disruption until the two transfer streams collide and will naturally head up the back of the cylinder wall setting up the loop scavenging.

during this filling of the cylinder with fresh mix any remaining burnt gasses that are not swept out will be trapped and dilute the next charge.

in theory we want 100% fresh charge in the cylinder for compression. we are trying to increase performance in many ways by attempting to increase efficiency by 2 percent here 4 percent there. Throw it out the window if your cylinder only has a 85% charge in it.

when the transfer streams hit the pop up what do you think happens? they go up right, its essentially a little ramp. when that happens the flat portion of the popup will have burnt gases sitting on top of the crown. That will be mixed in the next cylinder charge yes you have increased compression which makes this charge more efficient but it is a smaller charge.

I do think if a popup was gradual enough or small enough it could work but I think the squish cut is the better choice.

I think the real benefit of the cut squish is scavenging efficiency.


a popup has typically shown a performance increase compared to a saw that just has the squish set and not cut.

but what if we put a bigger charge that is more pure in the motor with lower compression?

David

Laminar in a saw will result in a couple of things in my mind that aren't going to make power. Fresh charge is more apt to mix with the burnt charge thus killing scavenging. Also resulting in fresh charge getting blow through the exhaust. Scavenging= efficient power in a 2 stroke regardless of its intended purpose (saws,bikes,boats and rc cars). The better it scavenged the cleaner the emissions as well which is why manufacturers are heading towards strato and delayed scavenging. We like to think saws are simple and power is great, but there's so many ways to make it folks tend to argue over it. There's scavenging diagrams and books galore but they don't fit the mold of a saw.

So what everyone ends up with is a few guys who are well versed with saws and are looking at different things, looking for the same end result which is more power. These are just my opinions and I'm not trying to ruffle feathers. A person shouldn't be ostracized for having an opinion after all its one of the freedoms we have.

 

[Mastermind]

One thing I have to keep in mind when I start getting carried away.........I'm not even really trying to get everything I possibly can from these engines. The first thing on my mind needs to reliability......

I had a guy send be a pic of a MS460 jug I did a few years ago that had the flange busted off. I offered to find a jug and fix it, but he said he was just gonna part it out........it had served him well.

Makes a guy wonder though........how much is too much?

 

[thomas1]

40%

 

[Trx250r180]

One thing I have to keep in mind when I start getting carried away.........I'm not even really trying to get everything I possibly can from these engines. The first thing on my mind needs to reliability......

I had a guy send be a pic of a MS460 jug I did a few years ago that had the flange busted off. I offered to find a jug and fix it, but he said he was just gonna part it out........it had served him well.

Makes a guy wonder though........how much is too much?

I have seen that in a few 460 jugs now ,seems the higher compression ,cracks them above the base on a few ,I have not had the problem myself though . Just because a few failed does not mean all will fail .

 

[walexa07]

One thing I have to keep in mind when I start getting carried away.........I'm not even really trying to get everything I possibly can from these engines. The first thing on my mind needs to reliability......

I had a guy send be a pic of a MS460 jug I did a few years ago that had the flange busted off. I offered to find a jug and fix it, but he said he was just gonna part it out........it had served him well.

Makes a guy wonder though........how much is too much?

Sounds like a casting flaw to me - that may or may not have broken just the same in stock form. Otherwise you'd expect a rash of your ported 460s to exhibit the same behavior after a good bit of use.

 

[cuttinties]

One thing I have to keep in mind when I start getting carried away.........I'm not even really trying to get everything I possibly can from these engines. The first thing on my mind needs to reliability......

I had a guy send be a pic of a MS460 jug I did a few years ago that had the flange busted off. I offered to find a jug and fix it, but he said he was just gonna part it out........it had served him well.

Makes a guy wonder though........how much is too much?

I have seen that in a few 460 jugs now ,seems the higher compression ,cracks them above the base on a few ,I have not had the problem myself though . Just because a few failed does not mean all will fail .

I'd rather take some reaming for only grabbing 25% and take my pride in a long lasting saw. 044/046 have weak cylinder bases and the 372xp doesn't have the strongest crank in the world. But some guy's are cool with a mail hauler and less durability. But some guys also wear tube socks with flip flops.

 

[Mastermind]

I'd rather take some reaming for only grabbing 25% and take my pride in a long lasting saw. 044/046 have weak cylinder bases and the 372xp doesn't have the strongest crank in the world. But some guy's are cool with a mail hauler and less durability. But some guys also wear tube socks with flip flops.

Well.........I have been that guy before.

 

[Hedgerow]

One thing I have to keep in mind when I start getting carried away.........I'm not even really trying to get everything I possibly can from these engines. The first thing on my mind needs to reliability......

I had a guy send be a pic of a MS460 jug I did a few years ago that had the flange busted off. I offered to find a jug and fix it, but he said he was just gonna part it out........it had served him well.

Makes a guy wonder though........how much is too much?

That is the model, not the mods.. Or so I have been told by a "Stihl guy"..
But good question none the less...

 

[Hedgerow]

Well.........I have been that guy before.

What do you mean "Have been"?

You ARE "that guy"...