What experience have you guy's had with putting either open or 4 hole spacers under the carb on single plane intakes??
I am running a 502ci with 9:00to1: compression, headers, 830cfm Holley carb, 226/234 w .591/.601, Dart single plane intake.
I was going to experiment with spacers and was looking for results from others.

Canfield makes an awsome spacer 12hp on the dyno

I am runing almost the same set up and added a 1' spacer plate. Didn't notice anything except it seems to act as a fuel chiller. If you put your hand on the spacer after running,it is all wet on the outside.

Not sure about the single plane, but on my Dual plane 509 built a little more stout than your motor I saw about 15 hp on the dyno(can't remember exact # off hand, but it was significant enough to make a difference). They can be tq killers though, so beware, because if you lose tq but gain hp, you are going the wrong way. My tq improved as well. 1" spacer.

Thanks guy's, I'm have tomorrow off and I am planning to go to a nice protected bay not far from my house to do a little testing.
I am going to start with no spacer and then try an open 1/2".
I have the four hole on now and it seemed to slightly improve low end over a 1" open , no real difference on the top but I did notice the plug colors are not anywhere as even with the 1" four hole as compared to the 1"open.
Supposedly the Dart is a well tuned manifold, maybe no spacer at all will work the best!
I just can't leave it alone !!

I noticed the write up on the new "tuned 4 holes X 1" Is this worth messing with on a HP500 with head work a 731 cam and the original Dart manifold or save a couple hundred bucks for fuel

No spacer is an end all be all answer to anything. A spacer can be used to help over come some problems in your intake tract (too large or small of a cam, head, intake, carb ect.)

General rule of thumb a 4-hole designed spacer will move you're power band down, giving you better tq, acceleration, and throttle response, while an open spacer will move the power band up giving you more top end power. The thicker the spacer the more of an effect it will have.

If your going to use one of the 4 hole spacers, you may have to do some dremel work to get the holes to align nice with the 4 hole gasket and carb venturis'.

use 4 hole cnc spacer provides 5 hp on dyno & cooler exhaust
tems canfield spacer

hmm i have to use a carb adapter on my 174 blower with a 1050 dominator. Its basically a 1/2" open spacer that bolts to the top of the blower and the carb bolts to it with offset screws. Will this effect the the output of my engine? I wouldn't think so becasue its forced induction and its above the blower. Am i wrong?