open vs 4 hole

[remytherat]

Putting a 4150 on an oem thermoquad manifold. Should the adapter be open or 4 hole?

 

[69FBCuda]

Is the manifold open or two/four hole?

If you use a four-hole gasket on an open spacer then the gaskets going to sag so you need to match the carburetor base gasket with the adapter. Also you want to consider Left Right idle setting versus open plenum idle setting.

 

[remytherat]

Manifold has a center divider. I have both types of gaskets

 

[RustyRatRod]

Manifold has a center divider. I have both types of gaskets

You don't need an adapter. All you need is this.
Carburetor plate

 

[junkyardhero]

the short answer is: it depends

you might be able to use the plate that RRR linked to, but the holley linkage might foul depending on the manifold. in that case you'll need an adapter spacer.

4-hole v open is hotly contested and there are dyno results that favor either depending on specific sets of circumstances (intake, cam, carb, thickness of said spacer, rpm range).

for a dual plane street engine i like the 4-hole

 

[33IMP]

I would think the divider wall of the manifold would .essentially with airflow and distribution with an open spacer/adapter.
I would go four hole.