Have a new 502 mag carb 415 hp stock, EMI headers, with a gm aluminum intake (brass lined cuz im in salt) and it was a 800 holley DP that hits the intake so i need a spacer. I was going to run one anyways becuse i read u can pick up a little top end on the dual plane intakes......anyways Do i want a open or 4 hole spacer and is 1 inch enough? What brands?

i run a 4hole 2in on mine it made the most hp on the dyno . the other thing is i am runnig a dart single plane intake

I run a Wilson spacer..

http://www.wilsonmanifolds.com/shop/...uct_detail&p=9

You would want to run a 4 hole. Jegs has a large selection of them. I know Teague motors come with 2" spacers on their carbed motors. Those Wilson ones are really nice but quite pricey.
http://www.jegs.com/c/Fuel-Induction...10289/10002/-1

I am running 2" hvh super suckers on my 496's. Every appication is probably going to be different than the other however I don't think you'll be disappointed with either. The 1" would work fine also. These things have always intrigued me as to whether they work or not. I have talked to several pro engine builders as well and always here the same thing. They definately make power. Again every application will vary though. I will be on the dyno in a couple of weeks and will certainly have results with and without. I also have Dart intakes.

I would love to hear your dyno results. I will tell you mine. They are correct....the spacers are worth some power. Everytime I take one off, I gain power. Seriously, I have tried so many different spacers and have always made more power without them. I also have a few other buddies that are engine builders that have said the same thing. I think in the heat on extended runs, they (phenolic, not aluminum) may help with heat isolation. On the dyno in a sweep, the spacers made less power. I have still left some in place for heat isolation anyway (phenolic spacer). Usually only a 1/2" open. We aren't talking about much power. Maybe 10 hp. difference with and without.
Eddie

For a dual plane intake, I would use a 1" open spacer.

We did two 515,s 9.1 comp dart heads merlin 4150 intake and the results with and with out a 1 inch HVH Supersucker was 2 hp at 5600 rpm. We did 4 pulls started without it put it on, took it off put it back on and got the same #'s 2 more hp with it on. That being said the Hp 500 arrester was a loss of 6 Hp to not having one at all. The K&N arester was only a loss of 1 hp.

Just my $0.02

I need one so my carb will clear the intake, not looking for bolt on hp but that would be nice too. the dual plane has a divider in the intake and with a open spacer can the fuel not go to the right side as good as if it doesnt have a spacer. I would think that a 4 hole would be just like the carb being bolted with out the spacer but allow more velocity. Im just tring to see which will work best and not lose hp!!

I asked a similar question a while ago and it led me to similar conclusions. I was told in general terms, the 4 hole works best with single plane manifolds and the open works best with dual plane. It has to do with individual port mixture velocities from the carb to create a semi scavenger effect or something.
Now though, I run a 2" HVH Super Sucker like Getrdunn does. It helps I think, but it also puts the carb up above the risers for ease of tuning! I tried a 4 hole briefly but couldn't seem to get the plugs to run even (so they come out the same colour), that's about as technical as my thought process got!

End result? I'd go a 1" open phenolic for the reasons Eddie said and if you can feel any difference, maybe try a 2" in future?

Good Luck!