Typically the longer and smaller the runner (dual plane) the more bottom end power. The bigger and shorter runner (single plane) requires more RPM to make it's peak power. The twist in that statement is this of course is a marine application where acceleration isn't as important as maintaining a steady RPM. I think that is why the single plane manifolds tend to work well in the marine world. Once we are at a steady RPM you can easily fill up the plenum and runners.

I am going to revise my peak torque rpm guess to 4800 +-.

I did not read all responses since I posted last, so sorry if someone posted this.

Nope. It's math. No matter what engine is measured, they'll cross right there. Torque is measured. HP is equated from torque, rpm, and a constant....constant being 5252. Thus while they'll equal each other at 5252 rpm.

HP= (Torque x RPM) ÷ 5252

That's exactly where the torque peak was for a set of AFR 265's with a single plane in this CC article - although they ran a more aggressive cam on a 454, so not exactly apples=apples.

http://www.carcraft.com/techarticles...r_numbers.html

That being said, I really want to limit my WOT RPM's to around 5400. This is a cast steel crank in this thing, not forged. Although they are supposed to be able to handle north of 600 HP, I'm not pushing my luck.

A big one with 'lower end' rpm with dual planes is that you don't have as much cylinder to cylinder (via firing order) intake air/fuel charge robbing, especially at low speeds.

The bigger the air pump (cid and/or great cyl heads with good cam) the less the dual plane is beneficial, even for our so called lower rpm engines. Especially with engines nearing 500cid or above.

Do we really care about power under say 2500 or so rpm ? Nope.

That said, there are many different single plane intake manifolds out there for BBC's. They are not nearly the same. Put a single plane designed for a 580+cid 7000rpm motor on a 454 and it will become insta-turd.

So...I always feel it's important when someone is wanting or suggesting a single plane intake that they mention which intake. Very important.

I have another one of these oval port Darts available if someone needs it. Send a PM if interested.

What works best with a 4/7 & 2/3 firing order swap?

I like how they proved ovals work better, by putting a modern designed aluminum oval, up against a 1960's designed GM iron rect head. Not to mention the GM iron headed combo was 9.7:1, with a major port mismatch, and the AFR combo was 10.5:1 port matched. HMM, I guess all rectangles suck. I would have like to see them do a back to back, with a 265 OVAL, VS a 305 Rect on that build. I bet the numbers would have been alot closer. Heck, a 308 Summit brand Iron head will walk away from those vintage 088 GM heads. They could have done a little better in trying to compare oval vs rectangle design.

So you own Dart oval port single plane intake and you are wondering which intake to use ..Why don't you put on the one you own and try it .If you aren't satisfied with midrange by an rpm airgap .Gaskets may be expensive .but less so than a new intake...Especially if you are happy with the dart and game over .....

Sell the extra Dart Oval intake, and pick up a used air gap for the same price. Then you could bolt the dart on for high speed runs, then switch over to the dual plane for pulling the tubers.