vacuum line for YICS?

[Brian Moffet]

I forget, what size?  My line to the front cylinder is going to need replacing soon (I can see it splitting.)

Thanks,
Brian

[Re-Vision]

Internal diameter needs to be 8mm or 5/16 inches. Outer dia. is 11mm.     BDC

[YellowJacket!]

I'm using Heavy Duty 1/4" (6.5mm ID) fuel injection line and it seems to be holding up and working quite well.  Its a bit of a tight fit so I guess Re-Vision is correct on the size that should be used.

David

[Re-Vision]

I just measured the YICS outer diameter at 8mm, hose inner diameter needs to be less than 8mm for a snug fit.    BDC

[Brian Moffet]

Thanks.  Because it's a vacuum line, it shouldn't have too much of a problem blowing off that pressure lines have.  I have 1/4 inch fuel line and that really feels too tight.  I think I'm running 8mm vacuum line on one of the lines, and have the stock (prone to splitting) line on the other.  I'll replace both while I'm at it.

Brian

[YellowJacket!]

I thought the YICS was pressurized not a vacuum.   ???  ???

David

[Lucky]

technicly, it's pulse...

[Brian Moffet]

Yes, it's a pulsed vacuum. Running on the original line, you can watch the line collapse and the go back to "normal" in time with the engine at idle. It's too difficult to see at anything higher than idle.  It is definitely not pressurized.  If I recall, it's tapped into the intake portion of the head above the valves. When the valve opens and the piston draws in the mixture, it creates a vacuum in the line/YICS.  When the valve closes, that line and the YICS then fills up with fuel-air mixture.

Because it is in the intake system, there is no time that it is above atmospheric pressure.

Brian

[Re-Vision]

Curiosity made me go and look at a head. You described it well, Brian.     BDC

[supervision]

  The placement of that port is right over the stem of that one valve. Must have been wanting to stir the mixture, or swirl it.  Maybe we ought to try yikes on just the rubber intake boot, and cap off the head port. Should be some affect of yikes.

[Rikugun]

Because it is in the intake system, there is no time that it is above atmospheric pressure.

Does that include the two periods of valve overlap - the shorter duration at TDC and loger period at BDC?

[Re-Vision]

Wonder if the purpose of the YICS is to smooth out the vacuum changes as each cylinder draws air in? Don't see how the vacuum could ever go above atmospheric.    BDC

[YellowJacket!]

ahhhh, your're right Brian and thats why I replaced my YICS lines with a more solid hose.  I remember seeing that early on on YJ.  I thought it WASN"T supposed to collapse but apparently I was wrong.  I've got some vacuum line I may swap out and see if there is a difference.

David

[Brian Moffet]

Does that include the two periods of valve overlap - the shorter duration at TDC and loger period at BDC?

I believe so.  The only time that the valves are both open are at TDC (ish) is when the exhaust upward stroke is finishing and the intake downward stroke is starting.  The only time the valves are open at the bottom is either valve but not both. The reason that the intake valves stay open is to allow the mixture to fully move into the cylinder, which implies a positive pressure from the intake manifold vs the cylinder. Because of that, the intake manifold will always be mostly higher than the cylinder when the valve is open. That means that the intake manifold pressure will be at most atmospheric pressure.

If there is a time when it is is above atmospheric, it is short enough and small enough that it wouldn't pop the line off.

Do you have pressure curves on the intake manifold?  That would be interesting.

Brian

P.S. I'm working out the physics of this in my head as I type, so if you see a problem in my logic or have proof otherwise, I'd love to see it.

[Rikugun]

Agreed, I misspoke re overlap @ the bottom of the stroke  :-[  and no, I had no charts when I asked.
I was just wondering aloud after thinking about the pulsing of the YICS line.

You're right, the incoming mixture is moving rather quickly by the time the piston is at BDC on intake and it would be counterproductive to slam the valve shut there - thus the overlap improves volumetric efficiency at higher RPM's.

I later did some searches and found some interesting articles. I didn't save them but managed to find this one again: http://www.tfxengine.com/software7.html

There's several graphs showing intake and exhaust pressures. Unless I'm reading it incorrectly, intake pressure never approaches atmospheric. Interesting reading albeit dry and technical.