Crankcase Pressure

[avsfan733]

I was reading an article about the new Toyota NASCAR V-8 in "Racecar engineering" and they were talking about the relatively standard of running vaccum in the crankcase using the dry sump pump block...is there any benefit from doing the same in the head?

[graham bahr]

on almost all engines a vaccuum in the block would also be in the head as they are connected, i suppose it might help keep the engine oil tight and help prevent oil dissappearing down the valve guides, the main benifit i know of having a vaccuum in the crankcase is that it helps improve piston ring sealing as the pressure differential between above the rings and below them is bigger, and the majority of ring sealing is due to combustion pressure round the back of the rings pushing them harder against the cylinder wall ( which is why the top ring always wears more) and so as such theres not much benifit to having a vaccuum in the head

[Al Weyman]

also helps stop oil leaks on SB Chevy engines!

[RWC]

I've also read about crank vacume and seem to remember there were other benifits mentioned?
Anyone know of any more?

[Al Weyman]

The vacuum in the head area would only be in the area around the camshaft, rockers, cambox or valve cover or basically where the oiil flows, it would obvously ot be in the combustion area of the head. The advantages are as already outlined i.e. less blow by past the rings and better oil sealing especially aroud the cranshaft area and better oil control and that is basically it. David Vizard covers this subject, the benifits of negative crankcase pressure in some of his articles if memory serves me correctly.