Hello every one I had a 4 hole spacer atop my performer rpm air gap it really did not pull well.I have a sbc 383 rhs heads 180 cc runners 10.5 to 1 comp 236-242 @ ,050 .550 lift 110 lsa.670 worked avenger.
I installed a 1 inch open spacer....engine came to life and pulls hard mid range.
Seems an engine with after market heads and a decent size cam with a dual plane manifold do much better with open spacers.
How ever an engine with mild build like my 327 with vortec heads performer intake,600 eddy carb comp 218-224 @ .050 9 to1 comp run better with a 1 inch 4 hole spacer.Smaller builds need more velocity for the low end torque.
That is my conclusion after testing both engines with different spacers....
SO YES SPACERS USUALLY DO MAKE A BIG IMPACT ON ENGINE PERFORMANCE !!!!!!!!!!!!!