Thats what they say Randy. I ran a 1" 4 hole spacer on my old 440 that had the single plane Holley Street Dominator intake. It seemed to work good as I had a best 60 of 1.57 and best et of 11.49. I never compared it to an open spacer though. I am using a 1" open spacer now with my dual plane Indy intake and it feels strong. Ron