The t-slots can vary but need to be measured w bits but not just on the metering block face but underneath where the base mounts as they can and will be sized down in that location. Totally agree w/Al in that each fuel has it's burn rates and afr needs and see more power these days leaner like in the 13's and even low 14's than what was considered max power like the 12.5 range. I talked to a VP rep about the 101 unleaded I run and he said just because a fuel is oxygenated doesn't mean it needs richer afr's and my car screams in the 12.8-13.2 zone on the street and plugs look like new but not sure that translates into better et's yet...............Test and test again.............