Originally posted by Xterradon:
I do not think the positive pressure is pushing the piston down. [b]Do you believe vacuum is pulling the piston down on the intake stroke? I believe the piston is pulled down by the crankshaft as other cylinders fire. They do not all move up and down in sync.
There is not always vacuum in a forced induction engine. There is positive pressure when the supercharger is cramming boost into the cylinders.[/b]
In Brent's defense the combustion chamber of an Ineternal Combustion engine
ALWAYS has a vacume on an intake stroke. A supercharger just helps rush more air in during the intake (reducing the vacume and cramming more air into the cylinder).
How Stuff Works However I don't see how vacume would bring more oil up past the rings, the whole purpose of the top two rings is to keep oil from getting past.
One of the things I remember reading abut the Xterra in the sales brochure that Nissan sent me is that the pistons and cylinders are mirror polished from the factory.
Since the purpose of breaking in an engine is to polish the cross hatching off of the cylinder walls its seems to me that the Xterra engine would already be "broken in".
But I guess the rest of the engine and drivetrain need to be broken in too.
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