Topic: Check valve for breather when using pod filters

[Scott S]

 I read through some of the threads on what to do with the breather line when running pod filters. While there was mention of crankcase pressure I didn't see anything about using a one way valve in the breather hose. Something like a brake booster check valve or reed type PCV valve.
 The theory is that it lets the pressure from the crankcase escape but prevents it from pulling air back in.
 Thoughts?

[eurban]

Standard practice for crankcase breathers is to install a filter on the end to keep the rebreathed air clean.  There are filters are made for this purpose.  A one way check valve might be OK but I can't say whether there would be any negative effects.

[Scott S]

 Yeah, I'm aware of running a filter on the end. The one way valve supposedly will cause a small vacuum in the crankcase and prevent air from being sucked back into the engine through the breather/filter.

[Tim.]

MikesXS sells this sort of reed PCV valve - part way down this page.

http://www.mikesxs.net/products-40.html#products

The claim is a bit of a vacuum is maintained inside the crankcase, resulting in not only some marginal (and it must be pretty darn marginal) performance gain, but also less oil leakage through mating surfaces / oil seals.

[eurban]

How does the vacuum equate to performance?  Pistons are going up and down.  Those on the up stroke are "hurt" by the vacuum.

Later on, thought about it some more . . .Less air=less "wind resistance" for the back sides of the pistons as they come down. . . .

[Laminar]

How does the vacuum equate to performance?  Pistons are going up and down.  Those on the up stroke are "hurt" by the vacuum.

While an (ideally) equal force is acting on the pistons going up.

[Scott S]

 What about race cars that use a vacuum pump on the crankcase? I'm not sure about the science behind it all, but there's apparently some benefit.
 Minuscule, I'm sure, on an old motorcycle but it may help to prevent oil leaks.

[eurban]

Stock setup (at least on the later 750s) has the breather attached to the air box by way of a fluid separator.  This should help to create a small vacuum in the crankcase.  This was done primarily for emissions reasons no doubt.  Switching over to pods; just another simple mod that's not so simple after all

[MCRider]

How does the vacuum equate to performance?  Pistons are going up and down.  Those on the up stroke are "hurt" by the vacuum.

Later on, thought about it some more . . .Less air=less "wind resistance" for the back sides of the pistons as they come down. . . .

Perhaps its not so much the vacuum itself, but what the vacuum represents, which is lack of air. Less air less resistance to movement. Pretty marginal, but that's my guess.

[MCRider]

I read through some of the threads on what to do with the breather line when running pod filters. While there was mention of crankcase pressure I didn't see anything about using a one way valve in the breather hose. Something like a brake booster check valve or reed type PCV valve.
 The theory is that it lets the pressure from the crankcase escape but prevents it from pulling air back in.
 Thoughts?

I don't think you'd want to restrict the movement of air in either direction. It needs to breathe, hence breather.

remember that the early ones this hose was just left hanging, open to the atmosphere. No reason for not doing that.

On our roadracers we ran it to a catch can zip tied to a frame rail. Often just an OJ can. No restriction of air flow in either direction.

[MCRider]

I've seen some put a small K&N style air filter on the end of it, just hanging. Still no restriction to in/out air flow however.

[TwoTired]

What about race cars that use a vacuum pump on the crankcase? I'm not sure about the science behind it all, but there's apparently some benefit.

The crankcase vacuum in race cars helps keep the rings seated onto the piston lands, reducing blow by and increasing ring seal, thereby allowing more of the cylinder pressure to be exerted onto the piston top.  (And keeping crankcase pressure from pushing oil out oil seals.)

But, that race car vacuum is a lot more vacuum than you will get from the intake system of an SOHC4.

BTW, the PCV functional requirement is not for crankcase needs, but for engine intake vacuum requirements.  If you place the crankcase vent tube in the proper location, you don't need a PCV valve.  PCV valves are often located at an engine vacuum source after A/F mixture has been set, where adding more air (from blowby or crankcase ventilation flow through) would upset the A/F ratio.

Switching over to pods; just another simple mod that's not so simple after all

Yup.  What he said.

[Laminar]

Switching over to pods; just another simple mod that's not so simple after all

Yup.  What he said.

Well why don't you make a thread about it or something?