Sorry, I thought I posted this a hour or so ago, so may be repeating some of that which has already been typed... Duh..!!
Interesting thread on inlet tract fouling caused by the need to cut down on emissions due to the requirement to vent crankcase pressure and any contaminants contained therein back into the combustion chamber.
In times past the crankcase could be vented via an open pipe on the side of the engine that pointed downward to the road surface thus venting to atmosphere. as things "progressed" it was usual to find a tube connecting the rocker cover to the air filter to vent crankcase pressure back into the intake system...A sure sign that an engine was worn, would be the air filter becoming partly clogged with oil from the rocker cover vent..
It seems the introduction of direct fuel injection (D.F.I.) of the fuel into the combustion chamber increased efficiency and may have cut down on emissions in the process, but this equated to no fuel passing through the induction system part of which obviously includes the back of the valves, which would benefit to some degree in being washed with fuel to some degree..
With ever advancing technology, emission regulation, and the introduction of on-board digital management systems, there was a need to modify the system of discharging crankcase contaminants directly into the inlet tract to cut down on fouling of the inlet tract which had potentially increased due to the effects of D.F.I. thus Positive Crankcase Valves (PCV) were introduced in the hope of them catching the heavier contaminants and cutting down on the sludge build up in the inlet tract..
All of which seems better for the planet...? Perhaps not so for the volumetric efficiency of the engines or their max potential power output...?
I think I read somewhere that Mazda had introduced an extra injector into the inlet manifold of one of their D.F.I. engines in an attempt to minimise build up of sludge.. though that seems not to have been universally adopted..?
As to just how much it might be worth to have an engine inlet tract/valves etc cleaned I know not in terms of either MPG or actual power output improvement, though I suspect engines that are used mostly in slow traffic and for short runs, as ever seem more likely to foul up more than those that spend time being driven in a more sporting manner...? (-:
Also the more an engine wears chances are that build up in the inlet tract may increase.... piston ring blow by creating increased pressure in the crankcase and valve guide or seal wear creating more build up on the backs of the valves...?
As for thinking to solve the issue on a modern engine by just venting to atmosphere.... Hmm..? Dependant on when the vehicle was first registered I guess a wide awake MOT inspector might fail a machine with such a modification. Also worth considering is that other than Morgan (?) modern vehicles may have adaptive systems that monitor the emissions, crank case pressures etc.etc.etc. and may create an alarm relative to your crankcase modification....?
Just passing time thinking in type.. (-:
