Hi,
I don't understand why there is suddenly a need for extra breathers - if the original breather is not sufficient, then there is a problem with the engine (resulting in too many fumes). Adding extra open breathers just saps the power. During his experiments with the 'Plus' models, Eddy Withers found that a correctly timed breather gave a power increase of about 3HP at racing speeds. The timing of the breather is the critical part, depending on the revs at which the extra performance is needed, and the distance the breather is from the underside of the piston. As the piston descends, the pressure wave travels through the crankcase to the breather, and depending on the revs, the piston may be rising again by the time the breather valve needs to open. The timed breather on my DBD34 Gold Star does just that - it opens when the piston is rising!
Of course, reed valves overcome the need to time the breather, but all the air that comes and goes from the crankcase has to be pumped - and that consumes power!
Regards,
Eddie.