I reread the OP and realized he didn't mention what combo he currently has. My comments were under the assumption of a factory mag category motor.

After examining multiple 496/502/509/540 CID trend lines, (TQ/HP curves vs. absolute output) a pattern emerged regarding the single vs. dual plane combinations. The D/P is a fine manifold for certain applications (particularly OEM or aftermarket replacement heads), however, the better the head flows, the greater the restriction the D/P poses, as the flow numbers below illustrate. With a dual plane and lesser flowing heads, valve lifts ± .550”, the power curve would decay acceptably @ or near 5000 RPM. However, at the same displacement ranges, with good flowing aftermarket heads, optimized lobes, and valve lifts > .600”, output noses over significantly > 4800RPM with the dual plane.

The test data below is provided by Tony Mamo of AFR. Both manifolds are Edelbrock, mounted on the AFR 305 CNC chamber BBC head. Keep in mind as RPM and/or displacement increases the flow drop becomes increasingly significant. The goal was to determine which manifold had the proper plenum design, runner length, and CSA to support the upgrades to the package.

AFR 305 CNC Chamber w/ Radius Plate
Intake….AFR
.200”-----163
.300”-----241
.400”-----300
.500”-----344
.600”-----367
.700”-----368

AFR 305 CNC Chamber w/Performer RPM Manifold

Intake
.200”----158--- (-5)
.300”----224--- (-17)
.400”----272--- (-28)
.500”----305--- (-39)
.600”----324--- (-43)
.700”----327--- (-41)

AFR 305 CNC Chamber w/Victor Jr. Manifold

Intake
.200”----160---- (-3)
.300”----230---- (-11)
.400”----286---- (-14)
.500”----324---- (-20)
.600”----346---- (-21)
.700”----337---- (-31)

As the numbers indicate, the % restriction throughout the flow curve, are nearly double that of the Vic Jr. using the dual plane. An intake that killed off 43 CFM @ .600” lift would seem to be well outside the design parameters necessary to achieve optimum power. It would compound the issue that you have the 315 CNC heads that flow ± 20 CFM more than the test heads.

When building an engine package that is generating 600 lb./ft. early on in the curve, it is not optimal to attempt to pick up ~10 lb/ft early in an area that is rarely utilized at the expense of 15-20 HP at max WOT. Much of the press addressing the perceived “advantages” of a dual plane are targeted toward an OEM headed, stoplight to stoplight, scenario.

The Victor Jr. /Holley 950/1000 HP is the best combination I have seen for the AFR 305 CNC chamber/315 Full port, 489/496/502/509 CID marine packages to date.



Bob

Bob, you are very much appreciated for your great input and tutelage, we are being schooled by a master.

Very interesting it is mass vs velocity at a certain point sheer mass preform's more efficiently than velocity. Do I have that right??? I was always under the impression velocity won the day...I guess without mass who care's.

The two are always important. However, getting fixated on one at the cost of the other, won't help.
There's more to velocity than just carb size, intake runner length, and cyl head runner size.

More importantly, it is results. Not just on the dyno, but more importantly on the track, and on the water. These results are what prompted all this to begin with.

Remember, that 502 with AFR's, modern high lift , higher intensity HR camshaft is going to move a ton more air and subsequently a lot faster thru a Vic Jr than a 454 with old smaller intensity Hyd flat tappet cam, OEM rectangular port heads, and the same Vic Jr.

Now, build a 540-555 with AFR's, modern higher intensity hr cam or decent but reliable SR, and guess what ? Bring on the Vic 454R Dominator intake or equivalent, and go even faster. Still sub 6k motors.

We are in some very good years of hp building and it's only going to get better.

As I've quoted a billion times from Darin Morgan " Your motor is telling you what it wants. Are you listening ?"

thank you for everyones input there are definitely some very knowledgeable people here. I am going to go ahead and go with the single plane victor jr. And hopefully mid to late summer I am going to purchase aftermarket heads. short block on my engines are darn near bulletproof and very reliable, so Im sticking with The 454's for now! I think a bulletproof bottom end and an all new aluminum upper half will be just fine for what I need. thanks for the help!!!!

bore notching it wouldnt hurt either

With no other changes what impact would a dual plane intake have on a 502 mag

Are you oval or rectangle port? I think I have an oval port Vic Jr laying around that I'm not going to use.

Huh, learn something new every day. Might be time to look for a new intake manifold.