Is the 4 hole better or worse than the fully open hole? Or does it not make a difference. Putting this under my carb to raise the shaker bubble.

For a street car...better. The open one will want more rpm to work effectively.

Wilson Manifolds has a write up on the spacers. Not sure of the top, but a buddy that machines, builds and runs a lot of motors on his in house dyno says a 1 inch Wilson spacer almost always gains any V8 20+ hp and the 2 inch spacer gains even more.

Buy both and then test them on your car at the track

I did this, and the open spacer has always worked best for me. Even on a dual plane intake....

Completely dependent on the combination.

Thanks for the responses everyone. I don't think I'll be doing any track time w/ this Cuda. It ain't a show poodle, but too valuable to bust stuff (well, except for the 4.10 Dana). lol

Whats the combo? Cam, heads, intake, carb, trans?

Bone stock 440-4bbl. U code Cuda, w/ a 4 speed transmission.

If the intake has a the 4 hole flange, then I'd use a 4 hole spacer. If it's a dual oval hole flange...I'd be tempted to use an open spacer.

In a dual plane, adding a spacer allows all cylinders to get some of the flow from the opposite passages, like a small plenum (larger version of cutting down the left-right separator).
Low speed vacuum may drop. but peak power goes up.
More of my comments here: http://victorylibrary.com/mopar/intake-tech-c.htm#dp

there are some outstanding spacers made out of aluminum, usually the introduce nitrous and extra fuel. works very well and picks up a second or more off the ET slip

Great comprehensive article, Poly! Thanks

Use a dual spacer like the intake(2 oval holes) . I run an old wooden Edelbrock spacer on my 70 440 4bl. Not sure if they still make it though.

I've done lots of testing and as stated it's totally dependent on the combo and the plastic ones are not the best in terms of heat during heavy street driving. The phenolic composites are nice and actually keep heat out of the carb(s) by up to 35* on my stuff and the wilson tapered are so far the best at least for me....

Dumb ebody knob question , why does the shaker bubble need to be raised ?

My guess would be that it has the wrong shaker baseplate on the car, or the engine mounts have sagged and the engine is sitting too low.
But those are just pure speculation.

I miss ya too Jahnnny. lol

I've tested alot of spacer combos at the track and the open spacer has always worked best for me.

I usually keep my carbs on the smaller side - I like 750's and 850's.

Perhaps with a bigger carb results may differ.