Just installed a new Holley Strip Dominator to replace a Performer RPM after having bigger valves installed on my 427 big block. As a rule do you jet up when going to a single plane intake? Jet down? or just run it and check the color of the plugs? Also what plug should I run? I like AC plugs but I'm not sure where to start. The higher the number the hotter the plug? Heads are late'67 3917215, solid roller of unknown origin .652 lift not sure on duration. 2.19,1.88 valves appox.10.5 compression, Holley 750 DP with ProForm main body. Thanks for any advise.

I would jet it up! your plenum is going to increase as is the height ,as you increase the plenum you go leaner! I would try going up 2 jets at a time .

Jason, Thanks for responding. I'll jet up a few sizes, throw in some fresh plugs and see what I get. The car ran 12.38 before the bigger valves and intake swap. I'm hoping to get into the 11's. Going to the track in a couple of weeks, we'll see how things go.