In a dual plane there is a split down the center of the chamber the carb bolts to. What this does is seperate the intake runners to the heads into 2 sides. A single plane is open under the carb and all 8 runners feed from that area. For the most part dual planes make better low torque and less top end HP, single planes are better for high end HP and running at high RPMS. Most of the time street cars gain from low end torque (get moving grunt basically) than from top end HP. But I recently changed from a vintage dual plane cobra intake to a modern single plane weiand and got a 40hp difference at the wheels in the top end with a bunch more space under the curve across the rpm band. It also moved my peak HP up about 500 rpms, but I also got more torque out of it too. Not saying this will happen in all situations as it depends on your motor, but I was amazed.
Actually theres more to it than the divided plenum, you can have split plenum single planes as well. Dual planes are what they are because one side of the plenum has a higher floor than the other side, aka different planes. Single planes all 8 runners feed off the same level within the plenum.
Single planes are also perfered for forced induction setups, as well as large nitrous shots when using a plate (you can direct inject it and it doesn't matter).
'72 Mach 1
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I thought they were dualed for the purpose of having a smaller chamber to draw from and not have as much volume drop when getting the air to start moving. the dual level is the only way to make that happen without having several cylinders drawing off the same bank as I understand it. The single plane is a more straight through design (closer to a tunnel ram if you will) so you get more up high power out of it. But I will never say that all that is not hearsay or that I am remembering it wrong.
Jumping in here... Point of clarification: All dual plane manifolds are likewise dual plenum. However, the opposite is NOT the case. Dual "plane" manifolds are also called "180 degree" manifolds. These will have the plenum floors at two different levels because each plenum feeds 2 cylinders on each side of the motor (4 total)... the differing "planes" allow the intake runners to pass over/under as they cross to the other side. The "180 degree" name is because this intake runner configuration allows each plenum to feed cylinders at evenly spaced intervals of 180 degrees crank rotation. If you consider the firing order of a typical V8 you'll see that a non-180 degree dual "plenum" manifold will have a rather eratic pattern for drawing intake charge. I believe the Holley "Street" Dominator was a dual plenum of this type, except that there was a balanceing port at the rear intended to equalize intake pulses. At any rate, for the street, a 180 degree dual plane intake will generally work best.
recently changed from a vintage dual plane cobra intake to a modern single plane weiand and got a 40hp difference at the wheels
That's a pretty impressive change, considering the typical improvement when transitioning from a stock iron manifold to most aftermarket ones. What is the build-state of your engine? I noticed, on a stock long-block, a fair difference going from a stock iron dual plane to an OEM Cobra dual plane but it was nowhere near what even 20 RWHP would do. IME, at the track at least, the dual plane combos, while sometimes a bit slower (no more than .08-.1 seconds) have been more consistent. Using a high stall converter (over 4K) brought the single planes I've used into this consistency range (.05 or less repeatablility). Current W has a Performer RPM on it and I've been pretty satisfied with its torque band and repeatability. Makes good power into the 6.5K range without sacrificing the low end, since I've been using a much tighter 10" converter (3.2K flash).
BTW, although I don't have access to a engine/chassis dyno, I do have extensive track time with most of Edelbrocks's single and dual plane products over the last 25 years. Guess I'll be looking at Weiand on some future projects. Thanks for the tip...
I think that was kinda what I was understanding about the dual planes...just don't know enough to describe it that well.
I chased all over the place and was not getting the power that I should have out of the car. This was using a mustang dyno. I tuned the car (carb and dist) on the dyno and got all that I could out of it. With makeing no other changes with the exception of up jetting the carb changed to the weiand x-cellorator and saw that amount change. I could not believe it myself. 4 speed car. Its a ford 345 horse 302 with the x heads, b303 cam, long tube headers, 2.5 flowmaster setup and holley 650dp. The dyno printouts are here:
I have a 351C I am rebuilding, so I've spent a lot of time at the 335 engine series forum... The Weiand gets a lot of recommendations over there as being very streetable for a single plane with a nice broad torque band. There is a Pantera guy who just posted a build for a customer using a Comp Cams 282S & an Edelbrock Performer. The horsepower topped out around 375 - 380 IIRC. The builder said he tried to talk him into the Weiand; said with just the manifold swap he would have been over 400 in both hp & torque... sounds good to me.
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