Crankcase vent vacuum setup removal = bad

[ducatiz]

prove it wrong.

Plenty of people have removed the crank vent vacuum setup, but based on my research, this is a bad thing for any engine.

I am just surprised that kits like the TPO crank vent kit are still sold.

Both BCM and Jon Nichols have said the stock setup is best since it makes a vacuum in the crankcase so blowby pressure doesn't stress the engine seals and provides a reservoir in case oil is spit out the vent:

The following is a earlier post by BCM Ducati:

What is different about Ducati streetbike breathers in general is that the reed valve is mounted directly in the case. The breather box location and volume are good.

The reed valve location is good for emissions but not for engine power and crankcase breathing. What happens is that under certain conditions, under high rpm and light load, the oil doesn't run back because of the reed valve and it builds up in the tube above the reed.

The simplest solution is to hollow out the reed assembly and leave it internally open but still hitched to the volume bottle. This allows the volume of the breather bottle to perform its function and usually gives a slight horsepower increase also.

Then, use either a 748RS reed valve in the airbox at the end of the breather hose, OR, use a Ford diverter valve (in-line one way) just before the airbox.

The following is a earlier post by Jon Nichols:

We firmly believe the best system is the stock system. Let me expand on this. The only part worth replacing is the breather itself, and only if it is leaking or if you want to dress-up your bike. We see many Ducati's with the K&N filter attached to the breather hose. This is simply not a satisfactory replacement or alteration to replace the stock system. The stock system is less restrictive because there is more volume making it less restrictive.

Part of the problem with this modification is that the only efficient replacement systems made were made for race circumstances. This was accomplished by increasing the tank volume into which the engine pumps. On the early bikes, 851, 888, 955 in the 851/888 chassis Ducati had a very large carbon fiber tank which was connected to the engine crankcase without any breather. The tank was mounted in the tail section of the bike. This effectively doubled the crankcase volume and was responsible for an additional 3 to 5 HP at high RPMs.

This type of system is also available for the 748/916/996 chassis. This type of system is not available for Monsters or SS models, unfortunately. Therefore, the system that allows you the largest volume to pump into is the stock system. This system pumps into the airbox and has the added benefit of a collection/separation tank between the crankcase and the airbox.

[scott_araujo]

I'm with you, it will generally lower engine performance.  How much for a particular engine?  Who knows.  I think people still love to do this mod for two reasons:
1) In the old days when smog equipment was introduced on cars almost every piece of it lowered performance.
2) The bike just looks cleaner when you take more parts off.

Scott

[Bill in OKC]

The TPO kit does not remove the reed valve - there is still a vacuum in the cases.  It replaces the plumbing between the giant PCV and the airbox.  I have seen a picture of oil all over the back wheel from removing the plumbing, but after a year and a half, it has not happened to me.  I would do it again.

edit: I actually added an automotive PCV to my Aprilia that didn't have one stock and noticed an improvement.

[ducatiz]

The TPO kit does not remove the reed valve - there is still a vacuum in the cases.  It replaces the plumbing between the giant PCV and the airbox.  I have seen pictures of oil all over the back wheel from removing the plumbing, but after a year and a half, it has not happened to me.  I would do it again.

How is there a vacuum in the case if you remove the vacuum source?  The TPO kit removes the hose that connects to the airbox -- which is the vacuum source. 

The reed valve has nothing to do with the vacuum except to prevent backflow.

The crankcase itself has pressure, not vacuum.  We hooked a meter up to it and got almost 2 bar from it (which is about 30 psi) when the engine was revved and that was on a factory version M800.  I imagine the bigger bikes will produce a lot more pressure.

[Bill in OKC]

I'm not the expert, but the expert stories, the guys who figured this stuff out, indicate it is the positive pressure from the pistons coming down forcing air out of the valve and when they rise again a vacuum is created.  After a few revolutions there is a constant vacuum in the cases.

[Sgt_H]

What's the crankcase vent vacuum setup?

[ducatiz]

I'm not the expert, but the expert stories, the guys who figured this stuff out, indicate it is the positive pressure from the pistons coming down forcing air out of the valve and when they rise again a vacuum is created.  After a few revolutions there is a constant vacuum in the cases.

so where does blowby go?

And is it possible you misunderstood?  Every source you can find on 4-cycle engine operation states that the crankcase will have a positive pressure, NOT a vacuum.

The pistons are reciprocating without a valve, so they do not affect crankcase pressure/vacuum at all.  The issue is blowby.  The higher the engine turning the more frequent the blowby and therefor, the more internal pressure, not vacuum, the crankcase has.

That's why engines without a vacuum hose attached (sometimes called PCV) blow their seals.  If it was a vacuum, they would SUCK the seals in.

Posted by: Sgt_H
What's the crankcase vent vacuum setup?

The hose on top of your engine.  It is connected to a reservoir which is in turn connected by a hose to your airbox.  The airbox provides vacuum to the reservoir and in turn to the crankcase to suck fumes and blowby out of the case.

[ducpainter]

Both of my Ducs have the stock crankcase vent system for exactly the reasons stated.

[Bill in OKC]

The blowby goes out the one-way reed valve the same as the positive pressure generated by the pistons falling.  The one-way valve keeps air from coming back in.  I can see a possible advantage having the hose going to the airbox if you have a restrictive air filter but think about this - and this does not necessarily apply to a monster but more a 999s - or anything with a pressurized airbox/ram air - what happens when you are trying to create positive pressure in your airbox at high speeds from a ram-air effect?  In that case you would have a positive pressure forcing air back into the hoses.

[Sgt_H]

The hose on top of your engine.  It is connected to a reservoir which is in turn connected by a hose to your airbox.  The airbox provides vacuum to the reservoir and in turn to the crankcase to suck fumes and blowby out of the case.

Thanks, Just wanted to make sure you weren't talking about the smog canister that I just took off. 

[ducatiz]

If the blowby goes through the breather, then you just contradicted what you said before -- the crankcase has positive pressure, not a vacuum

In your hypothetical of a ram-air type airbox, you would have a different kind of airbox setup and a separate pump for the crankcase, which is what F1 cars do.

Also, there are other sources for vacuum, such as having a plenum directly off the manifold, which is how Ducati does the evap emissions box for all the later bikes.

[Bill in OKC]

The blow-by is there whether you have a K&N or the factory setup...  The whole idea is to let it out of the cases as efficiently as possible and then prevent any drawback.  If I had any problem with my setup, I would be the first to admit it and change to something else.  If I was really ambitious I would plumb up my O2 sensor bung and make it into an exhaust scavenger.

If you look at the factory setup for a 749/999 you'll see a pressurized airbox (ram-air snorkles connected to a sealed airbox) connected to the crankcase vent tube.

[Capo]

Load of BS

Check this out for the real info

http://www.ducati-upnorth.com/tech/breather.php

[ducatiz]

Load of BS

Check this out for the real info

http://www.ducati-upnorth.com/tech/breather.php

that's where i got the quotes from BCM and from Jon Nichols. 

Bill, maybe you can do a little more checking around, but every reputable source I can find on the web has indicated the opposite of what you're claiming -- that the crankcase is pressured, not vacuum.  If you google PCV or crankcase pressure, you'll see that the only issue is blowing seals, which is due to pressure, not vacuum.  no one talks about crankcases sucking in their seals.

Seriously, just go out to your bike and hook up a flow meter to your breather.  I have done it.  You'll get around 20-30 psi on a new engine and more on an old one.  That's air pressure, not vacuum.

[hooligan machinist]

Or, if you don't have a meter. Just start the bike and remove the oil filler cap. Be prepared to clean up a bit though.