I am running a mildly built 454 mag and looking at possibly switching out my Hardin Marine/Dart single plane intake. I've got a 800-holley, rect. port gm iron heads, a full roller valve train with a mild cam running 9.8:1, though lightening headers.

I am most interest in cruise effeniency/speed (3800 rpm) put still want to be able to put up the speed when needed.

How would a dual plane aircap style manifold compare to my present setup?

I would think my best change to boost the midrange would be in the heads but I want to keep them(rect. port) for my next rebuild. I think I'll go stroked (502) and blown (Whipple). Should be a whole new experince after that.

What do you think about the intake. Is it worth spending the time and $

Vegas,

A 454 will give you better midrange response with a dual plane intake manifold. This is especially true with a mildly built 454 as you describe. The rectangle port GM heads are really kinda large for a 454 inch marine engine, and will kill torque, and throttle response. With your rectangle port heads, a dual plane intake should help combat the sluggishness ---esecially in the user friendly rpm ranges of a 454" marine engine.

If you were thinking of an Edlebrook "Air-Gap" dual plane intake manifold then I would say you're off to a good start. You might even be able to get away with an oval port design intake and still bolt it on to the rectangle port heads as that would greatly help your torque numbers as well. I would definately check into that. Perhaps cstraub69/Chris or rmbuilder/Bob or someone else can chime in here on your situation.

I think you have a very good setup right now, depending on where your wot rpm lays. The double pump 800 is well suited for a single plane intake. I personally like the rect port and would chose them over the oval port for any performance type application. If you are looking for a change in performance I would look at the cam and rpm range desired.

BT