Just mounted up a new Holley Dominator and have a choice of either a open hole 3/4" Phenolic Spacer or a Hamburgers Billet 4 hole 1"Spacer.
What are the Pro's and Con's of each?

Post a picture looking down into the top of the intake

If your Dominator still has internal linkage, at minimum you need a 4 hole shear plate. It keeps linkage parts from mixing it up with your valves and pistons.

The only way to know for sure which one the engine will like, is to test.

Buy both of them and then sell the one you don't like
Don't forget to stack them together also before deciding

You don't need a shear plate for an internal linkage Dominator, you do need a safety plate, if you use an open spacer to make sure if anything happens it don't get in the engine. A 4 hole spacer does the same thing. 20ish bucks from summit or jegs

As for which spacer you need, there is no magic formula. If it is a street strip deal Id likely just use a 4 hole, wont need the safety plate that way. As for which will work best a lot of factors in that equation, as stated only way to know is try both. One will give you a better signal to the booster the other ads to plenum volume.

That's what I meant. Thanks, Al.

4 hole is for torque,open for top end

I run a minimum of a 1/2 wood four hole then if you have room an open for the mid/upper power but like stated, it's a trial n error deal.......

I like the small 4 holes wood ones as well. Need a safety plate anyway so may as well get some heat sink benefit from that