If you are running the standard ECU and MAP sensor then you will HAVE to have the frequency limiter. I know the frequency limiters are not available any more but I am looking into making them myself. I made a copy of the Turbo Technics 5th injector controller as mine died. Turbo Technics had the octane adjust pins grounded continuously but I found that it works a lot better if they are shorted through an adjustable vacuum switch. You set it so that it only grounds the pins when the inlet vacuum doesn't exist any more (i.e. you're coming on boost). This way you don't loose any of the off boost performance.