262XP Day
- Thread starter Mastermind
- Start date
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Mastermind
Work Saw Specialist
I'm gonna get to take part of April off.
I don't think it will quite do it either. Close I bet.
Lightening......
What?
Yeah, that's how we do it.
Eccentric
Mister Wizard
You leave out the FW side bearing? PROOF that DuH1984 contributed something to the MasterMoobs shop afterall....
Mastermind
Work Saw Specialist
Eccentric
Mister Wizard
http://www.arboristsite.com/community/threads/262xp-day.277547/page-5#post-5305652
Reread yer post carefully. Follow the steps and the pichurs....
Reread yer post carefully. Follow the steps and the pichurs....
Eccentric
Mister Wizard
262XP Unibearing Edition.
Mastermind
Work Saw Specialist
Spare parts.......
Meh
Meh
Mastermind
Work Saw Specialist
cuttinties
ArboristSite Guru
Less friction=more pizz revving?
Eccentric
Mister Wizard
Optimum blend.
drf255
BAD CAD
I'm still trying to wrap my head around this.
So by what I'm seeing and what you're saying here Randy, piston speed is the fastest at mid stroke, then slows from top to bottom. This would make sense, because at TDC, dwell time is present. So zero piston movement despite crank rotation.
So piston speed must be represented as a sine wave.
So in essence, when you lower a jug, even when you cut an equal popup, you're changing the timing of the jug, period. Whenever you move the port away or towards the centerline of the crank, the degrees of rotation that cause a fixed amount of movement will change.
Removing a fixed amount of material, anywhere, is going to affect the timing numbers as it's a non linear relationship.
So in theory, if I cut the jugs that I've already ported with the numbers you've shared, the BD will change even though the ports aren't moved in relation to each other.
So by what I'm seeing and what you're saying here Randy, piston speed is the fastest at mid stroke, then slows from top to bottom. This would make sense, because at TDC, dwell time is present. So zero piston movement despite crank rotation.
So piston speed must be represented as a sine wave.
So in essence, when you lower a jug, even when you cut an equal popup, you're changing the timing of the jug, period. Whenever you move the port away or towards the centerline of the crank, the degrees of rotation that cause a fixed amount of movement will change.
Removing a fixed amount of material, anywhere, is going to affect the timing numbers as it's a non linear relationship.
So in theory, if I cut the jugs that I've already ported with the numbers you've shared, the BD will change even though the ports aren't moved in relation to each other.
drf255
BAD CAD
Also wondering how piston speed at opening and closing points affects port function and placement. Dolmar's have weird numbers, small cases, and long looking jugs.
You gained 5.5* of blowdown just by moving the jug down without touching a port.
You gained 5.5* of blowdown just by moving the jug down without touching a port.
Paragon Builder
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Great post!
drf255
BAD CAD
S0 an intake port should be open for the most amount of TIME because of where it's placed in the chamber. Piston speed would be the slowest of all the ports.
Sorry if I'm giving anyone a headache here, but does the top of the transfer port need to be covered by the rings before the intake opens to I sure no intake back through the transfers?
I'm sorry if I'm hijacking this into a porting theory thread. I'm just trying to make it all click.
Sorry if I'm giving anyone a headache here, but does the top of the transfer port need to be covered by the rings before the intake opens to I sure no intake back through the transfers?
I'm sorry if I'm hijacking this into a porting theory thread. I'm just trying to make it all click.
Slacker. I thought you'd have these done by now. After all, I can do this many saws in 5-10 weeks.
cuttinties
ArboristSite Guru
Piston speed is the same. The only way to change piston speed is by affecting stroke. The length of time in which the port is open is relative to the Dwell time at top dead center. That's affected by the rod length/stroke. But considering that saws are very short stroke I don't believe that the Dwell time isn't affected quite like you're thinking. Going by chordal width and duration the exhaust is usually open longer, and has more time area than the intake.
cuttinties
ArboristSite Guru
My phone likes to capitalize the word Dwell.
drf255
BAD CAD
How could it be the same?
Look at Randy's numbers. How did his intake only move 2.5*, the exhaust 3* and the transfers move 7* if piston speed was constant.
The piston is moving a different distance per degree of crank rotation at different points.
cuttinties
ArboristSite Guru
Unless you change the stroke piston speed is not changed. What you're seeing is affected more by crank angle than piston speed. The longer the stroke the higher the piston speed. This is why Randy's exhaust height guidelines work so well for him. Higher piston speed allows for higher durations. What appears to make the piston slow or dwell isn't slowing the crank down. For the time you're considering the port open the opposite is closed. So the intake isn't open longer than the exhaust. The durations of the transfers are affected because of the fact the location on the cylinder.
Look at the intake or exhaust ports and you'll notice that they reset (repeat their cycle) very much sooner before the transfers. Another thing to remember is that a smaller port is covered faster than a larger port. Which means that the durations will be affected quicker.
old-cat
Fir Man
You guys are just TOTALLY over thinking! Trial and error is the only way you can make engines run better.
