Ok. What is the main purpose of these spacers that go between the upper and lower plenum? If I recall some say it will cool the upper better therefore your engine will gain in performance from cooler air. I also know sometimes you may want to run them if your valve covers are to tall. Now the question I have is how does a longer runner effect the intake RPM range? You see currently I have an stage II ported edelbrock performer that flows ~275cfm (if I remember correctly) and was using it with an anderson b2 cam. Now however with my new 331 and the n-91 cam which is a high rev cam up to 6900rpms my intake will be running out of steam at about 6000rpms maybe more because of the port work. So I was thinking of picking up a Holley Systemax intake and getting the lower ported to match the Stage II ported TFS heads. However, if a spacer and longer runners help out the rpm problem I may save myself some money and try it. However, I'm thinking that the upper plenum is probably very much involved in determining the RPM range not just the just the lenght of the runners on the lower. If the longer runners from a spacer do help, how much? Am I just better off in getting the Holley? You see I'm trying to make a 500HP N/A 331.