Here's the deck surface of the bock before lapping. This is cleaned already with cleaners, rags, etc.
This is the block's surface after I hand lapped it. If you want a metal head gasket to seal, this is going to be step one. Hand lapping produces a smoother finish than machining in most cases.
After the block comes back from WPC, all porting completed, all of edges and casting parting lines are deburred, decks lapped, the block gets ultrasonically cleaned at Cosworth. The deburring and lapping is standard Cosworth practice. Then as a final cleaning, it goes into the FMT or “dishwasher” its called by the builders. In the picture above is a bunch of moto-x cylinder heads, but blocks go in there too on specific fixtures. The block is rotated constantly and sprayed with an aqueous cleaning solution by a gazillion squirters at high pressure. If you have a Cosworth engine, I'd strongly recommend you have it rebuilt there when needed if not for their cleaning equipment alone. Of course they have some of the best engine builders in the business.
Cosworth VQ35HR head gaskets are used in the ARK Design GTR engines. The HR head gaskets change up the water flow compared to the DE. There's an article explaining the differences onJim Wolf Technology's website. The weakness of the factory Nissan gaskets is that there isn't enough water flow flowing through the exhaust areas of the cylinder head. The Cosworth gasket retains the factory HR cooling scheme to keep a high performance street car or occasional track day car happy. Since I consider Time Attack an extreme use situation, I opted to modify the head gaskets.
Here's Katsu modifying the gaskets by hand on the mill. Since the Time Attack engines are ultra low quantity, it is cost prohibitive to make a custom head gasket. I'm not ever going to use a custom head gasket so modifying the Cosworth gaskets was the only solution.
To improve overall and increase water flow around the exhaust areas, holes like this were added on the gaskets. Perhaps in the future, I'll have some water jetted for a cleaner and quicker solution.