[Rotary Evolution]

i would say it likely has to do with carburetion versus fuel injection, giving the less efficient fuel setup less room to expand between the 2 flame fronts to increase efficiency of the carb versus the later model fuel injection.

but the differences are going to be very minor and not likely worth worrying about.

i would be willing to bet that any direct injection engine in the future will show an even further gap between the plugs and more a retarded leading plug position(moved down in the housing). i doubt you will find much research outside of the mazda papers on this, it's simply too much work doing back to back comparisons. even ambient condition changes and minor setup differences would skew results.

it would be interesting to know the exact benefit and drawback of each, but i'll be damned if i'm going to go through it all. heh. i'd also be interested on the difference of running leading only ignition versus the trailing assist in performance, i do plan on doing some testing of those combinations but it will not be on a carbed engine(well maybe, maybe not. i do have a customer with a turbo REPU which is carbed and currently running leading only). moving the lead plug position is just a royal pain to get actual figures, comparisons and results from.