RobertPaulson

The heat damage is consistent with running for a very long time after the bearing has suffered complete failure. You've had a temporary starvation of oil at some point. Every one of those bearings shows it. The mains are polished and the bigends definitely show it. The bearings for cyls 1 & 6 are going to be the worst because they are the last in line to get fed oil from the main gallery in the crankshaft. The mains don't suffer the hammering because there is minimal lateral loads unless a missfire or detonation occurs. That's why they are just polished. The rest of the big end bearings partially survived because when oil supply was regained, they continued to be lubricated. 1 more second without oil and #6 would have looked like #1 does and another 3 seconds and the rest would look like #6 does now or worse. There is only 0.0001" difference between what #6 looks like and what #4 & #5 look like. That's all it takes. The damage was done and then you continued to drive it for what looks like maybe 1000 miles. You probably didn't hear it due to exhaust noise and the fact you might have been relatively gentle on your new engine. It's disconcerting that the oil pump hasn't failed. That would be an easy find. Are you sure there is no crack in the inner or outer gear? You have to look very closely (by the sounds of your descriptions you know what you're doing) Also measure the outer gear in 6 places to make sure it's still round as well as the inner gear if you can. I don't think this is going to be the cause though. Any idea what clearances were run?

It looks nothing like sand damage

Sorry for the late reply. What do you mean? I've done plenty of -5 setups with cams on stock stroke GTR's and they make a bar of boost at 4k if your tuner knows what he/she is doing

You don't have a 'head drain', you have a crankcase ventilation pipe. Restricting oil to the top end of a hydraulic head is a fairly silly thing to do. If you have converted to solid lifters or have the Neo 25 head, then this is not so much a problem. They need the quantity of oil in the head for a reason and this was designed into them because smart people know what they are doing. The absolute best thing you can do to stop oil from venting into catch cans is to have adequate ventilation from the crankcase (block) and adequate baffling in the cam covers. I would suggest an RB26 cam cover changeover and fit the Mines or Hi-Octane baffle kit. This kit, along with your ventilation pipe is all you need. If you must bang restrictors into your block, just use the Tomei ones. They bring the size from 2mm down to 1.5 which is a substantial decrease in oil quantity.

If you're at 4000rpm in second then you should be on boost and response won't be a problem.

Check the depth of the housing to the old blades and see how far off they were. By cutting it back where you are saying they have, I think, would reduce exhaust temps by passing gasses onto the exducer much faster. If it has been cut there and you are sure of it, it's possibly to do with the small housing it has