Hey guys a stupid friend of mine owns a 66 chevy II / Nova, I helped him fit a pair of Aeroflow heads with an Edlebrock dual plane intake. We were mucking around with different carbs and spacers. Now, a dual plane intake has the divider so it only uses 1/2 the carb yeah ?? With an open spacer it could use all 4 barrels yeah ?? I confused... Is the engine running on 1/2 a carb when carb is on without a spacer or with a 4 hole spacer an on all 4 barrels when the carb is on a open spacer ?

Are we both stupid ?

A dual plane feeds 4 cylinders from one half the carb and the other 4 cylinders from the other half of the carb. Doing this increases the length of the runners and in theory makes more power down low where a street driven car can use it.

Single planes feed all 8 cylinders from the whole carb and has shorter runners. This in theory provides more top end power where a race car can use it..

Dyno tests have shown that good dual planes, like the Performer RPM, don't give up much top end to a good dual plane. Of course the rest of the build is important too, it's all gotta work together.

Aye mate, I would suggest a "dual" spacer to match the center divider on the intake

I would use either a four hole spacer or a spacer that had the slot from the front to the rear the on the same side so the carb. is still seperated from the other sides signal

Pontiac guru Jim Hand (his boy Tom is a member here) thought keeping the primaries separate and opening the secondary sides to each other gave the best of both worlds. Low end response with increased top end.

To learn more on this
single/dual/ best runner length
subject,
I would suggest studying the:

Dual carb extra long runner Chrysler manifold on 413 ci 300F

1992 5.2 Magnum V8 "beer barrel" intake manifold and how the center divider changed,

1994 Iron V10 25 inch runner intake manifold

1994 Viper aluminum V10 intake manifold

2003 year 5.7 Hemi intake manifold

Later years variable length 5.7 Hemi intake manifold

Chrysler has provided a kinda "school" about intake manifolds in those designs.

It is also worth reading about how Ford had a actuator valve in their variable length runner intake manifold, then found that they could leave the valve off and let "the airflow decide" which path it desired to go down.

Also

http://victorylibrary.com/mopar/intake-tech-c.htm

As stated, the divider is there so each plane only feeds from half the carb. This is done to increase vacuum signal to the carb, which boosts low speed torque and throttle response during normal driving. This is why fuel injected engines are essentially single plane because vacuum signal to the throttle body with a port efi injector would be worthless.



Runner length is a totally different phenomenon from carb spacer on a common plenum intake. Without getting too technical, having the correct runner length gives you a power boost at certain rpm ranges due to harmonic pulses inside the runners. However to get this at any useful RPM, the runners need to be long, like 18-25 inches long typically, and as little as a 1" difference matters. This is why modern v8 intake manifolds look like a bunch of curley fries all stacked side by side. The old chrysler 413 long ram manifolds were a carbed example of this. Since this is impractical under 95% of cases, the aftermarket doesn't bother. It should be noted, runner length only matters if it happens BEFORE the common plenum.