The Sportster and Buell Motorcycle Forum - The XLFORUM®

The Sportster and Buell Motorcycle Forum - The XLFORUM® (http://xlforum.net/forums/index.php)
-   Sportster Motorcycle - Bottom End (http://xlforum.net/forums/forumdisplay.php?f=205)
-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (http://xlforum.net/forums/showthread.php?t=2073932)

Hippysmack 5th August 2019 18:52

Quote:

Originally Posted by needspeed (Post 5767859)
For what you're trying to find out, wouldn't that work just as well as a manometer?

Possibly, but what fun is that? :laugh

I held off even trying since Aaron once posted he tried one with no real result.
But we don't know exactly what his criteria was.

I'm wondering if the slack tube would react slower and more constant than a vacuum gauge.
But looking at the testing so far, the biggest variants would be at idle and upwards of 5000.
(unless there is a problem that needs addressing)
Would the vacuum gauge work too fast to be usable?

needspeed 5th August 2019 19:18

I can only relate what happened on the one bike I used it on. At idle the gauge needle fluctuated rapidly from negative to positive readings. I wonder what a manometer would show in that circumstance?

Just above idle (1500 rpm) the needle showed a rock steady vacuum. Small, but a vacuum. Remember though that my system is a bit different than the one you're working on.

Quote:

Originally Posted by Hippysmack (Post 5767861)
...Would the vacuum gauge work too fast to be usable?...

Why would that matter?

Tomcatt 5th August 2019 19:53

Quote:

Originally Posted by needspeed (Post 5767859)
I've used an automotive vacuum gauge, usually used to measure intake manifold vacuum, to measure crankcase vacuum on my old ironhead. It will read negative and positive pressure.

For what you're trying to find out, wouldn't that work just as well as a manometer?

Yes it will, it's just that they usually read in in/HG and aren't as sensitive as a gauge (or manometer) reading in in/H2O. It's just a matter of what range is needed.

Tomcatt 5th August 2019 19:56

Quote:

Originally Posted by needspeed (Post 5767873)
I can only relate what happened on the one bike I used it on. At idle the gauge needle fluctuated rapidly from negative to positive readings. I wonder what a manometer would show in that circumstance?

Same thing. This is where easily adjustable damping (think needle valve) is nice to have.

You also have to keep in mind that longer and/or smaller ID hose running to your gauge or manometer will also damp your reading.

Hippysmack 5th August 2019 20:17

Quote:

Originally Posted by needspeed (Post 5767873)

Why would that matter?

I just pictured it working as it did on the carb and if so, it bounced so much I could get a reading.
It's good to record above idle readings but as in my idle to throttle deal with the cap off,
It'd also be good to be able to see what's happening at idle.
Dammit, the bowl seal had to break now....

60Gunner 5th August 2019 20:32

I think what was discovered was during braking and acceleration with the at the full mark, oil ran into to line at times and I stead of draining into the cam check, followed there instead. At least that's what they figured was happening.
There, now ya read that on the internet too.

Tomcatt 5th August 2019 20:42

Quote:

Originally Posted by 60Gunner (Post 5767894)
I think what was discovered was during braking and acceleration with the at the full mark, oil ran into to line at times and I stead of draining into the cam check, followed there instead.

So what?

That has nothing to do with what is being talking about here which is reading pressure/vacuum by tapping into the vent line.

Tomcatt 5th August 2019 20:45

Quote:

Originally Posted by Hippysmack (Post 5767892)
I just pictured it working as it did on the carb and if so, it bounced so much I could get a reading.

That's why you damp the gauge. Some gauges have adjustable damping built in.

dieselvette 5th August 2019 21:07

Quote:

Originally Posted by needspeed (Post 5767873)
At idle the gauge needle fluctuated rapidly from negative to positive readings. I wonder what a manometer would show in that circumstance?

I think the fluid's resistance to movement (mass) would cause it to move a lot less than a gauge. On the other hand, without an orifice or needle valve to dampen the reading I suspect the fluid could blow clear out of the tube or be sucked in. All depends on your setup. If that happened then suddenly you've compromised your breather system by adding a vent - start over.

Which is why I would start with oil in the tube and use a needle valve, and after playing around with it until comfortable then maybe switch to water for a more standardized measurement.

I don't mean to be presumptuous, but my take on Aaron's testing is essentially that direct measurements don't matter - dyno results is what matters. There are only so many ways to modify the breather setup, and certainly all options have been tried in the racing world. So if you're experienced with these motors then trying to measure is probably an unnecessary step in the diagnostics. And I think we're really going off on a tangent playing with this, but it's educational I guess.

bustert 5th August 2019 21:25

does all of this really matter???
my grin factor says no.
a dyno run is just a tool, nothing else and to be honest, a good dyno run and real world is two diff animals.
you can have two identical engines and one dyno's out with more of everything and then have one that produces more after-peak power, which one would i take, sure, the long winded one.


All times are GMT +1. The time now is 07:01.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, vBulletin Solutions Inc.
XL Forum® - Linson Media LLC