RB bearing clearances and oil flow tricks

Improving Rb30 block oil supply. Hello I have an rb30 bottom end i am building to run with an rb25 head, The block had already been fitted with aftermarket oil squirters when i received it. I am intending to run 800bhp and 8000rpm through this motor. Can anyone with RB experience advise of optimal bearings clearance? (currently 1.8-2thou mains and 1.8thou big end)

Also I have heard numerous different ideas about increasing oil flow including drilling the the top mains oil feed and bearing out to 7mm, Placing shims in the oil pump to bring pressure up, And having the block machined with angular groves trailing from the mains oil feed. Can anyone confirm which of these will actually work? Or any other oil flow tricks. I know these engines are renowned for mediocre harmonics and oil supply problems.

Oil pump being used is a stock rb25det pump with reimax billet gears

I'd aim for around 0.002" on the big ends and 0.002-0.0025 on the mains. Rather than re post, this thread covers the key aspects in improving oil supply in the RB series of engines. Check it out and let me know if you have more questions:https://www.sau.com.au/forums/topic/110680-oil-control-in-rbs-for-circuit-drag-or-drift/

Hi Andre. Thanks for the reply I will order a set of 1thou loose mains bearings and go half/half to get 2.5thou mains. I've already implemented most of the oil control modifications mentioned on that SAY thread in terms of keeping oil from filling the head.

The modifications I was asking about are in relation to improving flow of oil to the bearings themselves. I've attached an image of an example where someone has milled a slot into the block side of the mains bearing, drilled out back to the oil gallery with a 7mm drill bit then fitted an rb26 bearing to the block.

I was curious if these oil feed tweeks are commonplace modifications in terms of building high-ish load rb30s? Or if you think they are unnecessary.

Cheers James

I've never personally made the modifications you've mentioned and I don't believe they will be necessary or essential. Ultimately opening up the gallery from the bearing journal to the main oil gallery isn't going to hurt as the oil flow will ultimately be limited by the bearing clearance anyway. One modification I have made is to the alignment between the oil supply hole in the bearing shell and the oil gallery in the block as often there is a misfit between the two.

In the Nissan world it's not uncommon to groove the journals in the block of an SR20DET so that you can use the GTiR bearing shells which have multiple oil supply holes. It's not a bad option and I've done it myself but really have yet to prove a clear advantage from doing so.