Got this to complement my Nismo engine oil cap. The Nismo radiator cap has a opening point of 1.3kg/cm2 compared to 0.9 for the stock radiator cap. The higher pressure actually raises the boiling point of your radiator coolant/water thus resulting in better cooling. This is provided your engine's cooling circuit is able to handle the additional pressure. Do not try this on Protons as leaks will occur at the radiator hose joint points. Don't ask me how I know. Was assured by Alan that this wouldn't be an issue and that the radiator cap and my car's warranty would be unaffected. Closeup picture below of Nismo radiator cap in packaging.
As far as I know the radiator cap is common across most late gen Nissan's including R32/33/34, S13/14/15, N13/14/15/16, B13/14/15, etc. Part number is 21430-RS012. Picture below of the radiator cap installed. Looks very shiny and bling eh? :P