Popup vs Flat Top?
- Thread starter Mastermind
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it's to late man. old-cats already here. this is just gonna get all serious and such. wait til mudstain mike shows up. all the fun will be sucked right out of this. may as well lock it now
c'mon buddy, we can let the adults talk after dinner and have the kids play in the next room.
we used to do it all the time during the Holidays...the problem starts when the alcohol gets flowin...then the beer muscles kick in
Its NOT 5 o'clock ANYWHERE now !!!!
Hedgerow
HACK
I got an idea as to why you can get away with a pop up in certain instances vs a cut band..
Not that it would be my preferred method, but there is a trend developing here..
Not that it would be my preferred method, but there is a trend developing here..
Big_Wood
westcoast dweller
Wiggs gave me some education on the phone last night.
it's to late man. old-cats already here. this is just gonna get all serious and such. wait til mudstain mike shows up. all the fun will be sucked right out of this. may as well lock it now
Oh and if the fireworks start going all you have to do is drop a few "gratuitous" Boob pics...Boobs always STOP arguing...you cannot argue with boobs....
everybody loves boobs....and the resulting "pop-ups"
Big_Wood
westcoast dweller
doesn't boobs get a guy banned here? we should just bribe SS to post a boobs pic under harleyT's username so he can permaban him.
Hedgerow
HACK
And you understood what he was saying?
I dont wanna see any of your pop-up's
Big_Wood
westcoast dweller
man it would suck if 08 found this thread right now.
brilliant !!!
SS is chasing him around like the Coyote chasing the RoadRunner !!! ( you might be too young to remember them days)
i don't think it's a fair/accurate comparison, because the 261 is the only m-tronic saw ........
a damn good m-tronic non the less...
i think a standard 261 would most likely show the some power curve as the others in the 1st graph...
i really hope you guys can stay civil in this discussion, cuz i kinda like both of you ..
a damn good m-tronic non the less...
i think a standard 261 would most likely show the some power curve as the others in the 1st graph...
i really hope you guys can stay civil in this discussion, cuz i kinda like both of you ..
Moparmyway
Its just a saw
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it's to late man. old-cats already here. this is just gonna get all serious and such. wait til mudstain mike shows up. all the fun will be sucked right out of this. may as well lock it now
You are gunna have to stop making me spit my drink on my computer ............... if you keep this up, it might get expensive for me, I am already on my second screen
Mastermind
Work Saw Specialist
Picture this in your mind......
Think about what happens to the air/fuel mixture as the piston closes the squish area, and that popup starts going up into the combustion chamber.....
Think about what happens to the air/fuel mixture as the piston closes the squish area, and that popup starts going up into the combustion chamber.....
Theory is all good and fine, but real world difference is what matters to me.
Those cases where the exhaust needs to be lowered is an entirely different discussion. I'm speaking directly about flattop vs popup. All port timing and compression the same.
Those cases where the exhaust needs to be lowered is an entirely different discussion. I'm speaking directly about flattop vs popup. All port timing and compression the same.
Moparmyway
Its just a saw
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Well said ............. I agree 100%
Chris-PA
Where the Wild Things Are
I'm not convinced, but I think it is an interesting question. It seems to me there are two times when an obstruction on the piston top might change important flow.
The first would be when the transfers open - here the piston in moving downward, significant cylinder volume has opened up, and the exhaust port has just opened (with lots of turbulence from the flow from pressurized exhaust gas blowing out the exhaust port). The transfers will open up to several times the height of any reasonable pop-up or dome.
In this picture of a (tall) pop-up you posted the other day I can see the wash patterns at the transfer outlets. They look a lot like what I've seen on flat top pistons, but then I don't have much experience. You can see wash on the edge of the pop-up though, so that would say it's being deflected some:
On this domed piston there is no edge to hit, but the other wash pattern is similar:
Anyone have a good picture of a flat piston with wash?
What happens without the obstruction? Those gas flows will meet each other in the middle and be deflected (assuming they are not exactly cancelling), probably upward.
The second would be near TDC as the air is forced out of the squish band and flows across the top of the piston. The velocity of moving gases will be much higher under this condition, and the pop-up is of similar height as the squish clearance. The gases will be deflected upward anyway - do they get deflected sooner because of the pop-up edge, or do they turn up at the edge of the combustion chamber anyway?
Doesn't the mix need to go up into the combustion chamber anyway? If the popup is going to deflect anything, it's going to deflect it upwards.
