Topic: Vent to exhaust

[bwaller]

Hi guys,

I wasn't able to find anything in a search, but I seem to recall some discussion a while ago about plumbing the top end vent into the exhaust. I have made a thin wall stainless pipe between the header and a GSXR muffler on my 550 and could easily weld a fitting in this pipe to run the vent into.

It's either this or buy a vent filter to use.  Any other thoughts?

[rhinoracer]

Isn't the stock vented down to the pavement? Otherwise it's better to plumb it to the intake so it'll have negative pressure.

The exhaust has positive pressure and will just blow exhaust fumes into the engine unless your top end vent pressure is greater to overcome the exhaust pulses.

[bwaller]

The easiest solution is just to vent to atmosphere, but I do remember reading somewhere that it was vented into the exhaust, probably a high comp. engine. I'm sure it could be made to work even if a mini one way flapper valve was needed to block any greater pulse pressure than what the engine generated.

If anyone knows for sure....

[TwoTired]

I think may be mistaken.  It is quite common practice to vent the crankcase to the INTAKE side of engine, where the engine puts it into the exhaust after burning the hydrocarbons.

Honda did this with the 550 beginning in 74, and the 750 on 77 (I think).

You want positive crankcase ventilation not positive crankcase pressure.

I can't think of any application or desireable reason to make the crankcase pressure higher than the exhaust pressure.

Perhaps the engine you are thinking of had some kind of flow though ventilation?  Still I can't think of a good reason to have all those exhaust waste products contaminate the oiling system.

Cheers,

[bwaller]

I've been unable to find that info again, I believe it was a race engine. I'm only using the front part of the airbox with a large K&N in place of the stock rear filter box so will not run it there. I'll just vent to atmosphere.

Thanks

[Pinhead]

My 79 CB650 has the tube going to the airbox so it sucks the blow-by into the intake.

[ProTeal55]

People do this all the time with Big inch racecar motors.

They sell vacuum pumps which are spun by the crank, and basically suck the blow-by outta the valvecovers into alittle breather tank.On my my last car it was good for almost 40hp. Sucked on the street becasue I would have to drain the can of the oil/sludge as I drove the car or else the can would get full and spray everywhere..Another way people do it is just run a line/hose from each valve cover breather to a "bung" in the headers. Often called a "evac" system..

[dusterdude]

if you vent into the exhaust,you need a one-way check valve,like an air pump check valve off an older gm car,they are butt ugly,you could try to find something a bit prettier though.

[Stevien1]

As Proteal posted, you can actually use the exhaust to "pull" crankcase vapors out of the engine.  By welding a check valve in the exhaust pipe at an angle, the gasses flowing past create a vaccum and draw the crankcase vapors out of the engine.  The check valve prevents exhaust contamination back into the crankcase in the event of a backfire or durning low exhaust flow conditions (idle).

It works great on car engines, I was thinking trying it on my 550 one of these days....  I don't think it would work unless you had a 4-1 exhaust, however.  You need a steady exhaust flow over the check valve to draw a vaccum- something a 4-4 or even a 4-2 would be lacking.  In some automotive applications, you have to use a regulator inline to prevent TOO MUCH vaccum being pulled by the exhaust- it would cause the seals to be sucked in! 

[bwaller]

I kinda thought I could weld a fitting in at an angle on the inside of a bend in the pipe and use a check valve which could work, but I'll just vent the thing to air, keep it simple, stupid!

[kghost]

I put a PCV valve on the airbox of my 836 equipped K2

[TwoTired]

I put a PCV valve on the airbox of my 836 equipped K2

Um why?  Did you also put an extra vent to the crankcase to create airflow?

[kghost]

Because it needed one.

http://www.sohc4.us/forums/index.php?topic=19604

http://www.sohc4.us/forums/index.php?topic=1133.0

[TwoTired]

Totally understand why you need to vent the crankcase to the atmosphere and the airbox is reasonable place to put it.  I believe Honda did crankcase venting starting with the 750 F models in 75 and all 750 models in 77, including a water separator.

What I am asking is why you feel a valve is required?

IC engines need these when the crankcase breather is connected to the intake manifold.  The valve is needed so as not to upset engine operation during low vacuum.  The airbox has no such requirement.
Further, in places where a PCV valve is used, there is an air source going to the engine crankcase as well one to the PCV to positively scavenge vapors and pressure from the crankcase. 

I am also curious to know if your airbox insertion is before and after the air filter element.
Valve directionality would also be an interesting adaptation detail.

Cheers,

[kghost]

Its basically an adaptation of the later model bikes with the valve on the top of the aircleaner.

Tee'd the line from the valve cover to the oil separator.

Venting back to the engine occurs from the separator back to the bottom rear of the engine.

Works well.

Valve only works properly in one direction and its on the inside of the filter.