each spacer does a different thing,the super suckers work but only if you use the right spacer from the job.i'll give some cases, if the intake is to small in volume then you would use a open hole or if your not getting enough signal under the carb then you could go with a 4 hole. if the engine seam like it needs more intake volume and more signal you can use both . if you were to put a dominator on a mild big block and you can't get it to idle right and off idle through the first 2000 rmps are lazy and the timing and carb is close then you would put a 4 hole on it to increase the signal under the carb. but if you had that same big block that was built for all out drag and it seamed to run out of rpm early then make the intake volume lager with a open spacer.if you list all the stuff in the engine i could answer it better.