Originally Posted by
kingtal0n
well hang on. dont be so quick to judge these things.
If you start out at 100kpa and gradually climb to 95kpa then fine- its a pressure drop due to something, probably the air filter.
But if you go WOT at say 2,500RPM and see 95KPA then it can't be a restriction in the air filter or anything in the air path. Because at 2,500rpm the airflow demand of the engine is likely near half of what it is at say 5,000rpm. In other words, the engine only makes 200hp or so around 2,500 rpm (if that) so there is no way the air filter or anything else can restrict the engine to 200hp and then magically flow more as rpms rise later. See what I am saying?
If you see the same 95kpa at low rpm as high rpm then its likely a calibration issue, or the map itself is 'bad' (it might not be bad, it might just be reading slightly low voltage "bad" but still working).
It could also be a voltage issue, a ground issue, if the return voltage path is difficult due to poor grounding for example it can have that affect.
So next lets say it really is taping out at 95kpa. Well if the engine has a proper paper air filter, and an intact pcv system, then 95KPA is ideal. You need about 5 to 10kpa of pressure drop post air filter to drive WOT pcv action- to pull a suction on the crankcase at WOT. This does MANY things,
1. helps keep oil inside the engine and out of the oil baffles (out of the intake manifold)
2. protects oil seals (front/rear main & cover seals)
3. provides pressure drop for piston rings which improves piston ring seal and reduces blow-by
4. scavenge crankcase for combustion gasses which would otherwise degrade engine oil
So you really NEED and WANT a pressure drop post air filter, and a fully intact factory PCV system to pull on the crankcase at WOT, otherwise the engine will begin to lose oil seal integrity and start to leak, and it will continuously pollute the engine oil with combustion gasses, and the piston rings can't effectively do their jobs the way they were designed. This is perhaps the most overlooked aspect of high performance engines, neglected and dismissed at trivial when in fact it is one of the most important and highest topics of performance there is.