in the bike world, cylinders run leaner or ritcher depending on cooling (the inline 4's outside cyls run leaner etc). but i'd guess that in this case it is more function of the intake configuration. my guess. what pattern are you seeing?
On the front bank of cylinders I saw the spark plug closest to the throttle body darker than the spark plugs further away from the throttle body (I didn't check the rear bank yet). I'm not sure whether that's due to two of the injectors being slightly clogged and flowing less, my spark plugs being old and ageing differently, a weak coil, one cylinder starting to burn oil, the EGR feeding more into one cylinder than the other two, etc.
I'm installing cleaned injectors, new spark plugs, getting the coils and the compression tested, etc. on Tuesday and then I'll check whether the spark plugs "read" the same after that. Since the injectors are never perfectly balanced, I'd like to match the flow of the injectors to the fuel requirements of the individual cylinders in case the airflow into the individual cylinders is not perfectly even.
I read that in cars which have the throttle body off to one side of the intake plenum (like the NSX), the cylinders closest to the throttle body often get a bit less air at full throttle and the cylinders at the end of the intake plenum often get a bit more air due to momentum of the intake charge. Whether that's the case on our cars, I don't know.
It does make me a bit leery about removing the VVIS plate in order to gain a few top-end horsepower, though. Maybe the airflow into the cylinders is perfectly even with the plate in place and maybe it becomes uneven without the VVIS plate. Since it seems that the engine management system in an NSX cannot vary the fuelling of each individual cylinder, that could cause some of the cylinders to lean out even if the average fuel/air ratio is still correct.
