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Crankcase Scavenging

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Would using exhaust to create vacuum in the crankcase be worthwhile for performance or reducing oil leaks? I started making a catch can today and someone suggested this to me. Anyone done something like this to make up for lack of vacuum?
 
Are you going to use a juice bottle and tie straps for your catch can or are you going the fancy route?

They make small electric vacuum pumps.
 
You can add an additional vent at your clutch cover...We just put a 90 degree elbow, threaded into the filler cap and routed the hose back to the catch can....Just a thought...
 
I'm currently making a small aluminum catch can that I'm going to mount right behind the air filters, bolting it up where the stock air box would have connected. The only difficulty in adding a vacuum to this setup I foresee is the collector is almost entirely covered by the slip on exhaust can. I'm wondering if I cut the slip on an inch or so back if this will be likely to create a leak, and what I could do to get rid of it if it does happen. I'll try to post a picture of the can sometime.
 
gsbill said:
You can add an additional vent at your clutch cover...We just put a 90 degree elbow, threaded into the filler cap and routed the hose back to the catch can....Just a thought...
Click to expand...

I'm not sure what the purpose of that would be....
 
The purpose of that is, it works as another outlet to relieve crankcase pressure. Prostock bikes use vaccum pumps to suck air out of the crankcase, freeing up horsepower. That is the principal. Be sure your catch can has a small vent hole in it.
 
I've been thinking of using my other 3 vacum ports on my carbs and connect them to a single hose to the top of the valve cover breather. The fourth port goes to my petcock. Should be OK as long as there is not much blowby. Once there is a negative pressure in the engine it should'nt affect the carbs----I think?.
 
I think you will run lean if you do that Jake. Remember that the vacuum line to the petcock is a closed system - there isn't any flow, just negative pressure. The crankcase will provide more air to the carbs.
 
RacingJake said:
I've been thinking of using my other 3 vacum ports on my carbs and connect them to a single hose to the top of the valve cover breather.
Click to expand...
Run it to the air box and you have a nice stock system. It doesn't help the power to dump the dirty air into the intake. I would stay with a puke bottle and call it good.
 
It would be nice if it sealed this good. But even on a brand new bike or car check out how much crap comes from the vent. If you do vent to the intake, you can get away without a puke bottle in the rules. Just prevent it from getting on the track and everyone is happy.
 
Whoa...Thats a bad idea...Are you talking about venting from the top of your valve cover to your intake? That will cause you problems(oil) getting in with your fuel/air charge. That will hurt performance, not to mention HOT air...Cold air makes power...I have never seen or heard of that being done...
 
its done on cars all the time with a PCV valve so why could'nt it be done on a motorcycle?
 
I retract my comment about it running lean. I looked at the carbs and the injection point would not cause this condition.

Yes, cars do it - for emissions. It will reduce your hp. If that's ok, then I don't see a problem.
 
you still have me concerned about how it is reducing your HP, if your engine is flowing oil properly you wont get any through your valve cover vent hole. if you have a clog in the drain return somewhere then I can see how the oil can be pulled through. on a proper running engine the PCV system design can not reduce your HP levels. if you have lots of oil slop then yes the PCV system will contaminate your intake charge with another petroleum product and thus will raise the octane level of your fuel, but still uncertain on how it will lose HP. :-k :-k :-k
 
RacingJake said:
I've been thinking of using my other 3 vacum ports on my carbs and connect them to a single hose to the top of the valve cover breather. The fourth port goes to my petcock. Should be OK as long as there is not much blowby. Once there is a negative pressure in the engine it should'nt affect the carbs----I think?.
Click to expand...
Jake are you still ising the vacume petcock???
 
you still have me concerned about how it is reducing your HP, if your engine is flowing oil properly you wont get any through your valve cover vent hole. if you have a clog in the drain return somewhere then I can see how the oil can be pulled through. on a proper running engine the PCV system design can not reduce your HP levels. if you have lots of oil slop then yes the PCV system will contaminate your intake charge with another petroleum product and thus will raise the octane level of your fuel, but still uncertain on how it will lose HP.
Click to expand...
HP reduction isn't necessarilly from pulling oil. What you are injecting into the carbs is blowby. The oxygen content is much lower than the clean air you are replacing. Less oxygen = less hp.
 
Don,

Your cam chain slings oil right below that valve cover vent. Oil does make its way into that vent hose. Your crankcase gets" presureized as the piston go down, helping push that slung oil thru the vent hose... Any blow by will be in the crankcase as pressure, and will vent thru the valve cover...

Big high HP motors(PSB motors) use GM vaccum pumps to suck any built pressure out of the crank case..The word is, its worth about 15 horsepower...Keep in mind this is on a 25k plus, 300hp motor.

PCV is on cars to control emissions....When ya hop up a car, the first things to go are the emissions junk..Why suck hot, polluted, oxygen depleted air into a motor you re trying to make power with..

Jake,

Your idea is correct in theory, but it wont work the way you want...Skip it! It will cause you problems. Good Luck! Bill
 
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