The goal of a race breathing mod is to reduce crankcase pumping losses.
This is usually achieved in one of two ways :
- a much bigger breather pipe than standard
- a reed valve to reduce crankcase pressure
HOWEVER ...
if the engine has one piston in when one piston is out (e.g. a ducati v-twin or an ilf) ... then the pumping losses are not bad.
UNLESS ...
you have leaky rings
which will cause a big crankcase pressure problem and blow oil over your engine
SO ...
if your engine is blowing oil ... first sort out the problem, then worry about the after effects.