The problem Im seeing here is that during idle when the pcv valve is open and sucking gases and fumes (along with a little oil) it is also sucking air through the turbo intake port (clean/filtered and measured air), wasting some of its vacuum power due to the fact that this air passage is always open to flow. Apparently rb25 heads dont have any oil galleries that allow oil and fumes to move from intake side to exhaust side and vise-versa, hence the need of a crossover hose that connects both valve covers. With the rb's though, im having a little trouble understanding something. It creates suction in the crankcase while idling via the pcv valve port, and while underboost via the turbo intake port. IMO, this is the most optimal way to evacuate as much gases/fumes as possible from the crankcase. This is the way many cars come from the factory, including n/a ones. Stock rb's come with a valve cover mounted pcv valve connected post throttle body that only opens up for crankcase gases evacuation during idle, and a ventilation port that is always flowing connected to the turbo intake, between the maf and the turbo. I really hope we can discuss our different ideas in here since I've been giving it a though for some time now. Most piston manufactures recommend going to the first oversize and having the cylinder block bored to suit the new pistons with the recommended piston to bore clearance.Im trying to figure out my rb25det pcv system here and I though I make a discussion thread since I couldnt find a thread dedicated to the rb25 pcv, and the sr20 has a different system. Excessive piston to bore clearance tends to cause early and excessive blow by issues.
When using a used std bore there is already wear in the bore, hence the manufacturers piston to bore clearance cannot generally be met due to the existing wear in the used bore, especially after honing the used bore.
All piston manufacturers have a specific piston to bore clearance that they recommend. STD bore size pistons are not recommended in a used bore for any performance engine unless re-sleeving the block back to std bore size. We don’t keep STD bore pistons in stock and if you order these in we will not exchange or accept returns.
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