Just looking at this thread after a few months. #5 and #6 are the lean holes. Adding some clearance to the lean holes, *might* cause a little more oil in them than normal. The oil lowers the effective octane of the fuel. So you have the lean holes, more oil than normal. Good recipe for destruction.
We just finished a GT-R here in the US.2.6 liter (86mmx73.7) Dynapack numbers-rear wheel drive, 653 whp on 91 octane (PON) , 777.5 whp on C16. Laggy 2835's, top mounts. Its on an AEM with stock ignition. Good cold plugs($30 US)each.
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