More than 1 issue involved here, so please bear with me- I have seen several people mention drilling the IAC bleed hole oversize to allow greater flow for larger displacement LT1s. It seems to me like increasing the flow diameter would decrease the resolution of the idle servo, since there is more difference in flow between steps. I have seen in some other research, (and also seen used in carburetor applications) drilling small, fixed diameter bleed holes through the throttle blades to allow idle airflow with the throttle closed. It seems to me like this might be a good solution, allowing relatively fine adjustments with the IAC stepper without having it maxed out to accommodate the 383's airflow needs at idle. I bored the factory throttle body to 54mm (2.125") and used Holley throttle blades from a carb application. They came in a 4-pak, so if I drill too far I can swap them out for new blades. Is my thinking flawed on this plan?

Now for the other issue- In the course of installing a port-nitrous system under the manifold in the lifter valley, I was forced to machine away the underside of the manifold, thereby losing the small idle passages to the runners. I plugged the main passage that supplied airflow from the IAC to the small runner ports, and drilled a hole feeding the IAC air into the main plenum of the manifold below throttle body. I had noticed that one of the port feeds was a smaller diameter than the others, but I have no idea why. I realize that idle flow characteristics will be different, and that IAC stepper changes will have a slight delay vs feeding the idle air directly to the ports, but I am unsure if it will lead to other issues? Does anyone with more experience modifying the LT1 type manifold have any thoughts on this? I appreciate the input!