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Crankcase Ventilation

V6 Mark

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As I'm becoming more familiar with my new Mark IV Spitfire I noticed the crankcase ventilation hose has been disconnected from the carbs (which have theri short hoses blanked off) - the hose from the rocker cover now goes well it just goes down at the side of the engine and is not connected to anything.

Should I reconnect or leave as is? I've never really understood how introducing oily fumes into the carbs increases performance...


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sparky_spit wrote:
It doesn't!!  I would either leave it as it is, or better still fit a catch tank and run the hose to that. The ventilation connection to the carbs/manifold is to aid reducing emissions, it does nothing to help performance.

It is also supposed to cause negative/vacuum pressure in the engine and help stop oil leaks.

Ha ha it is Triumph they leak oil naturally.

If you remove it you may have adjust your mixture.

So is it worth the hassle just leave well alone.

If you where on 40's or what ever fit a catch tank.

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The 'standard' system is, as previously said, aimed at getting the slight -ve pressure (vaccuum) at the carb butterflies to help 'pull' fumes out of the crankcase thereby reducing emmissions and 'helping' stop oil leaks (HA-HA!).
The main problem with this idea is however that you only have a vaccuum of any note there when on a constant or trailing throttle.
At full or even part throttle when accelerating there is no, or next to no, vaccuum there anyway, and this of course is when you really need help reducing crankcase pressure !
As previously reccommended in this thread, leave the breather open (chances are it 'breathes' a bit anyway or else why would someone have changed it?), just make sure it's long enough and pref. use a catch tank of some sort (beer can will do).

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