Demonsizzler used to make this modification to his “Racing TQ’s” only for the serious racer. The thing is, you really don’t need to do this on most engines. He used Holley parts to get this done.
The primary butterfly drilling is easiest and quickest way to get done what you want done. The air bleeds are more for driving down the road or track when the blades are much more open.
This is where the AFR is affected by that mod.
