Exhaust crankcase sucker?

I know the basics - stick a tube in flow at 90' flat topped or
cut out like a carb spray tube.
But some I've seen weld tube at 45' angle to flow and
slice tube end to face squarely down stream.

I think I want to evacuate cases enough that any air the
scavenge gears inject into frame tank is below atmosphere.
Frame has low pressure relief valve but not yet over pressure.

Any advice or examples welcomed.
How far to stick into flow?
How big a tube for 920 size blow by?
Check valve needed?

hobot

That conversation happened a couple of months ago. try an advanced search.

I'm sorry grandpaul, can't seem to find terms to pull up this subject.

I pretty much found online how its done in various engines.
Mystery remains - will it prevent OIF from over pressurizing or
sucking air into oil pump.

hobot

hobot said:

I'm sorry grandpaul, can't seem to find terms to pull up this subject.

I pretty much found online how its done in various engines.
Mystery remains - will it prevent OIF from over pressurizing or
sucking air into oil pump.

hobot

Click to expand...

A reed valve might be more effective.

Reed valve recently display is a wonder to behold,
but I don't think by itself i'd pull pressure as long as Peel requires.
But it may just be the ticket for its check valve function hmm.
Will have to throw down bones and bits to decide.

hobot

hobot said:

Reed valve recently display is a wonder to behold,
but I don't think by itself i'd pull pressure as long as Peel requires.
But it may just be the ticket for its check valve function hmm.
Will have to throw down bones and bits to decide.

hobot

Click to expand...

I'm quite sure a reed valve would be more than up to whatever shenanigans you have in store. If I understand the philosophy correctly, once the reed valve has allowed the crankcase to reach near equilibrium it no longer has to sit there and flap like a epileptic seizure.

As I said I don't quite believe a reed valve will quite do it >
But I just don't know and I'm piqued to try it now and meter
the effects.

The wired issue is no venting to outside in her OIF set up,
* I hope*.

hobot

hobot said:

As I said I don't quite believe a reed valve will quite do it >
But I just don't know and I'm piqued to try it now and meter
the effects.

The wired issue is no venting to outside in her OIF set up,
* I hope*.

hobot

Click to expand...

Is there any reason not to vent the OIF?

hobot said:

I know the basics - stick a tube in flow at 90' flat topped or
cut out like a carb spray tube.
But some I've seen weld tube at 45' angle to flow and
slice tube end to face squarely down stream.

I think I want to evacuate cases enough that any air the
scavenge gears inject into frame tank is below atmosphere.
Frame has low pressure relief valve but not yet over pressure.

Any advice or examples welcomed.
How far to stick into flow?
How big a tube for 920 size blow by?
Check valve needed?

hobot

Click to expand...

The difference between the air intake and the exhaust is that the intake is all below atmospheric pressure already, the exhaust is above. As far as I can see, just sticking a tube in at 90deg to the flow will blow exhaust gases out, the pipe just uses the gas static pressure and that is positive all the way along the pipe until they come out of the silencer. Playing with the form and direction of your pipe end may produce a bit more depression by throwing up some vortexes. In order to get some real suck I think you'll have to add a venturi section and put it at the far end of the pipe.


I should say this is all a bit theoretical, not done it myself.

I saw in a book on the Norton rotarys that they used a rather large ventury setup on the exhaust to suck cold air through the rotors instead of running the inlet charge (before the carb) through rotor, apparently it gave a lot of free HP. The pressure drop may not be as high as you are looking for though.

Appreciate the various thoughts on this - gets me more data to ponder.

Swooheroo, oil scavenge pump has twice the out put of the pressure
side, my concern is that it may pump enough gas/air with the oil back
into the frame tank to over pressurize it to interfere with pumping out
engine sump.

Rick the back pressure in the exhaust system does exist more or less and must
be over come by the Bernoulli's Principle lowering pressure on a suction
tube enough to also evacuate the crankcase as low as it'll go.
If the velocity of exhaust pulse is enough, then it should work.
I've some headers to sacrifice and play with angle and ends and
size of tube on stock Trixie. If works on here with just one
header, it'll work on Peel's 2 into 1. Maybe hope so cross fingers.

College labs made use of Bernoulli's Principles and its a robust effect
if arranged right for the conditions. Robust enough that I plan on
making an air intake vent in the intake rocker cover to help
pull oil out of head and flush more moisture and corrosive
gases out the megaphone.

Cheezy, encouraging report of Norton rotary taking advantage of
this clever physics. The implied volume of flow also back
up my meager experience of remarkable robustness of the
suction.

Anywho someone's got to find out by the ancient accepted way,
try it and see.

hobot

Here's a link to a small amount of info. Grumpy Jenkins covers it pretty well in The Racing Chevrolet Engine. It's still in print.
http://www.eurospares.com/sucker.htm

As usual Bob you deliver the goods I crave. Dug up a 1996 'eductor' gem.
Below quote is what I needed most to know. Maybe a crayon streak
down the header will reveal the best place to poke into the draw.
One guess what I'd look for then shut er off. Then will move
tube in-out monitoring for depth into exhaust flow.

Oh yeah if not for you there'd be nil reason to bother with any
of this on Ms Peel.
hobot >>>>

So, when you cut into your exhaust system to tie in your eductor port, try to do so in a straight run, favoring a location closer to a downstream bend and farther away from an upstream bend. Avoid locations where the cross section increases, these locations trade velocity for pressure and are inimical to eductors. If you have to locate your port in a bend, locate it in the throat and avoid the heel. Avoid locating the tube so that it protrudes into the exaust flow. And finally, cut the tube that you are using for your port tie-in square, and locate it perpendicular to the long axis of your exhaust pipe and at the side or top of the pipe, not the bottom.

Gday Hobot, I tried to quote from an earlier thread on crank vents but made a hash of that big time!!!
Anyway by memory I quoted from Classic Bike 1988 where a drag racer in USA called Leo Goff vented his Commando dragster using hoses conected to inlet manifolds and exhaust. They were sepparated by a valve and which one had the highest vacum was, utilized.
Also my 4WD tractors in their exhausts, have a vacum pipe to vent excess dirt away from the aircleaner.Its not a venturie, just a pipe in line with the gas flow.
Rgds Puter Iliterate Foxy

Oh cool, never thought of taking suction form two sources
with a bias valve, clever.
Your revelation will leave me restless chewing on the added plumbing.
Anyone got a reed valve idea that's up to this new double task?

hobot