Adding venting to engine for catch can (race car)

[LateApex]

35 minutes ago, mlytle said:

curious......why?

 

having driven a lot of miles on race tracks with M10's, S14's, M20's, M50's, S52's, and more...i have never needed additional venting beyond the stock port.

That's great news. 

 

Why?  I've been paying attention to the race 2002s I've seen in the last 2 years and many (most?) had added some additional venting.  Just looking for some input and feedback.

[135i]

Search negative crankcase pressure benefits.

[Simeon]

5 minutes ago, 135i said:

Search negative crankcase pressure benefits.

 

That assumes that you are going to actually pull a vacuum with a PCV valve in the exhaust. Providing another vent into a catch can isn’t going to achieve that on its own. 

[02Pilot]

1 hour ago, Simeon said:

 

That assumes that you are going to actually pull a vacuum with a PCV valve in the exhaust. Providing another vent into a catch can isn’t going to achieve that on its own. 

 

Yeah, there's a lot more to crankcase ventilation than just adding a vent. You need to consider where you're drawing your vacuum from (pre-throttle plate/post-throttle plate/exhaust), whether you're planning to seal the crankcase or create a draw-through system, and what your target crankcase vacuum is going to be under specific operating conditions. If you go to a sealed crankcase with a high target vacuum, I suggest you give some consideration to the transition between on- and off-throttle conditions; you generally don't want it to slam up and down. Personally, I have found that I prefer high vacuum setups in engines that can handle them, but if you have significant blow-by this won't work well.

 

In a race motor, it may be hard to properly vent the motor fully, as you will have limited time at closed and light throttle conditions, and big cams are lousy for producing vacuum; I'm certain this is why you've seen lots of race motors with extra venting provisions. But it's hardly the only thing to consider.

 

For anyone interested in the inner workings of crankcase venting (albeit in a more modern application), look up the "02Pilot Mod" for M54 engines - I developed it after extensive research as documented in this Bimmerforums thread.