Crank Case Pressure/Vacuum Theory

[Termitebuffet]

I might have missed , but what difference in +/- pressure do we think we need to pulse the carb ?

Sawhawgz, ruining the internet since 2012...

 

[XP_Slinger]

I might have missed , but what difference in +/- pressure do we think we need to pulse the carb ?

Sawhawgz, ruining the internet since 2012...

I don’t think that was discussed and I have no clue...lol!

 

[Termitebuffet]

I don’t think that was discussed and I have no clue...lol!

If we think about the tiny pulse area , it won't be much in my eyes ...

Sawhawgz, ruining the internet since 2012...

 

[XP_Slinger]

If we think about the tiny pulse area , it won't be much in my eyes ...

Sawhawgz, ruining the internet since 2012...

I agree. I wonder how much it matters so long as it’s pressure and depression?

 

[Termitebuffet]

I agree. I wonder how much it matters so long as it’s pressure and depression?

I will see if I can check a pulse , while powering a saw with a drill ...

Sawhawgz, ruining the internet since 2012...

 

[Termitebuffet]

Rpm shouldn't change the pressure in my tiny mind

Sawhawgz, ruining the internet since 2012...

 

[Marshy]

I might have missed , but what difference in +/- pressure do we think we need to pulse the carb ?

Sawhawgz, ruining the internet since 2012...

More or less than atmosphere.

 

[Termitebuffet]

More or less than atmosphere.

So just flutter above and below ...I don't see it being huge

Sawhawgz, ruining the internet since 2012...

 

[wcorey]

Just because, I fired up a 2171 and clamped off the impulse.
Would stay running continuously, idle through about 3/4 throttle, including quick piss revs but cuts out pretty abruptly near wot.
The idle bumps up a bit almost immediately when clamped.

Fairly straightforward, didn't see the need to set up video.

No conclusions, just data...

 

[Marshy]

I agree. I wonder how much it matters so long as it’s pressure and depression?

That's a whole other topic of discussion.

 

[Chainsaw Jim]

WOT under load is when the real magic happens.

 

[XP_Slinger]

That's a whole other topic of discussion.

I’m deeply depressed now that’s for sure...lol

 

[XP_Slinger]

Rpm shouldn't change the pressure in my tiny mind

Sawhawgz, ruining the internet since 2012...

My tiny mind agrees. The piston is displacing the same volume regardless of speed.

 

[redline4]

Watching @Stump Shot video of the saw running, the guage shows a vacuum at idle and goes to a pressure at wot.

So lets say the diaphragm is going up and down.
At the point where the pulse goes from vacuum to pressure, does the diaphragm momentarily stop, then say reverse direction (going down/up) for lack of better words? Or does it just carry on doing what it was doing?
To me, if its going from vacuum to pressure, not only is the frequency of the pulse changing but also the amplitude.
To use @Fruecrue sine wave, wouldnt there come a point where the wave "twisted" on itself?

 

[Fruecrue]

Watching @Stump Shot video of the saw running, the guage shows a vacuum at idle and goes to a pressure at wot.

So lets say the diaphragm is going up and down.
At the point where the pulse goes from vacuum to pressure, does the diaphragm momentarily stop, then say reverse direction (going down/up) for lack of better words? Or does it just carry on doing what it was doing?
To me, if its going from vacuum to pressure, not only is the frequency of the pulse changing but also the amplitude.
To use @Fruecrue sine wave, wouldnt there come a point where the wave "twisted" on itself?

Looked to me in @chy_farm tests that pulse and piston are 1 to 1.
I think the gauge reading is misleading. The sine wave so to speak isn’t equal above and below the zero point so we see the needle seem to settle high.
Impulse tapping in the crankcase must play a role as does intake port timing.

I mostly made all that up on the fly.
How’d I do?

Since I’m making chit up, I’d also like to challenge the theory of @Termitebuffet that pulse strength is constant regardless of engine speed.
My minds eye sees a change due to mass air flow. If the throttle plate restricts intake, wouldn’t there be less primary compression, thus a change in impulse strength?

 

[Termitebuffet]

Looked to me in @chy_farm tests that pulse and piston are 1 to 1.
I think the gauge reading is misleading. The sine wave so to speak isn’t equal above and below the zero point so we see the needle seem to settle high.
Impulse tapping in the crankcase must play a role as does intake port timing.

I mostly made all that up on the fly.
How’d I do?

Since I’m making chit up, I’d also like to challenge the theory of @Termitebuffet that pulse strength is constant regardless of engine speed.
My minds eye sees a change due to mass air flow. If the throttle plate restricts intake, wouldn’t there be less primary compression, thus a change in impulse strength?

I'm loading the video now should be done by next Tuesday. ...lmao

Sawhawgz, ruining the internet since 2012...

 

[Termitebuffet]

Sawhawgz, ruining the internet since 2012...

 

[redline4]

Was that with the throttle plate closed?
Just wondering if the needle would move differently if the throttle was held open.

For many years I was always told to do car engine compression tests at w.o.t.
I've done back to back on same engine open and closed, my compression tester read the same.

 

[Fruecrue]

That’s come up a few times. I remember the subject, but not the details.

Was that with the throttle plate closed?
Just wondering if the needle would move differently if the throttle was held open.

For many years I was always told to do car engine compression tests at w.o.t.
I've done back to back on same engine open and closed, my compression tester read the same.

 

[Termitebuffet]

Was that with the throttle plate closed?
Just wondering if the needle would move differently if the throttle was held open.

For many years I was always told to do car engine compression tests at w.o.t.
I've done back to back on same engine open and closed, my compression tester read the same.

That was no carb at all

Sawhawgz, ruining the internet since 2012...