One issue with dual planes...is the cut out in the center divider is a fix for a symptom, and not a solution.
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True dual plane with a full divider, with a much larger carb, as each cylinder can only draw from 1/2 the carb CFM.

I'm interested in the good heads and dual plane impediment.

BSFC factor along with HP is also a good comparison.

There seems to be some good tunnel ram options these days. If I could fit them under my 420s, I likely would run them.

Tunnelcram

CMI Etops with long tail pipes. It’s a TRS boat.

Friends, there's an article that was written by Jeff Huneycutt of The Horsepower Monster series on YouTube from back around the end of 2016 when he visited the guys at Prestige Motorports in North Carolina who were conducting dyno tests of a NA 582cid 9.80" short deck BBC with various intake manifolds including the Edlebrock Air-Gap dual-plane intake manifold compared to a few various single-plane intake manifolds. They performed about 11 different tests according to the article, and the best results came with the dang Air-Gap dual plane intake!!! I copied and pasted TEST #1 of the article below and makes for some very interesting reading about the intake comparison results. I'm slightly surprised by the results with the Air-Gap dual-plane intake...I don't exactly know how fair or accurate these tests may be, but still very interesting...

TEST #1 Baseline: Brodix Race-Rite Ported Heads and Edelbrock RPM Air Gap Intake
Brodix CNC Ported Heads: BP-RR-BB XTR
Edelbrock RPM Air Gap Intake: 7561
HP: 705.8
LB-FT: 716.4
Interestingly, Prestige wanted to set a baseline for testing by going with what should be the best of the three cylinder heads that will be going on the engine. Brodix's new Race-Rite 24-degree aluminum cylinder head is designed to be an all-out performance head that still works with standard intakes and exhaust headers.


These heads are fully CNC ported from the factory with 119cc combustion chambers, 2.300/1.880-inch valves and a 298cc intake-port design that flows more than 390 cfm. We paired them with Edelbrock's RPM Air Gap dual-plane intake manifold.


On the dyno, the ported Brodix heads practically screamed. They made 716 lb-ft of torque at 3,900 rpm and nearly 706 hp at 5,900 rpm. We don't want to spoil it, but it was the highest output of any of the tests. Of course, the ported Race-Rite heads also come with the highest price tag. They usually sell for about $750 each (unassembled), which is fair for a competitive race car, but maybe a bit tough on the budget for a car crafter building an all-around daily driver.

Here are the remainder of all the tests completed in that article....

Test 2

Brodix 345cc As-Cast Heads and Pro-Filer Sniper Jr. Intake
Brodix 345cc Unported Heads: 2020003
Pro-Filer Intake: 206J
HP: 688.7
LB-FT: 683.2
For the next round, Prestige pulled both the ported heads and the Edelbrock Air Gap intake. In its place they bolted up a pair of Brodix's Race-Rite as-cast cylinder heads with 345cc intake ports. The idea is to check and see if the larger-volume intake port, which also flows more than 390 cfm, can make up for the improved quality of the CNC port tested earlier. Like the ported Race-Rites, we still have a 119 combustion chamber, so the combustion ratio is the same. The valves are also the same at 2.300 and 1.880 inches, and they are at the same 24-degree angle as well. But these ports are rectangular, where the others were oval. Not a big deal, except it requires a different intake manifold.
While we will eventually get to an equivalent Edelbrock RPM Air Gap, for some reason we decided to start off with a completely different intake: Pro-Filer Performance's Sniper Jr. single-plane intake. The Sniper Jr. is a big intake designed for engines pushing big inches. It is a relatively tall intake at 7.4 inches for the version that works with the standard 9.8 big-block deck height.
And as you might expect, the single-plane intake and bigger intake ports hurt the low-end torque. At the peak, torque dropped from 716 to 683 lb-ft. Peak power also dropped from 705 to 688 hp, and we also lost power under the curve as the average across the range dropped by 20 hp.
This combination was by no means bad. In fact, it was right in line with just about everything else we tested. Plus, the as-cast heads were about half the price of the fully ported versions. It does prove that it's hard to compete against a well-designed intake port that is appropriately small (the ported intake ports are nearly 50 cc smaller) for lots of port velocity while still moving a lot of air.

Test 3

Sniper Jr. Single-Plane Intake to Brodix Single-Plane Intake
Brodix 345cc Unported Heads: 2020003
Brodix HVH 2000 Intake: 2007
HP: 676.9
LB-FT: 676.2
Brodix's HV 2000 single-plane intake manifold has similarly sized and shaped ports as Pro-Filer's Sniper Jr. used in the previous test, except it has a shorter plenum with a total height of 7.185 inches compared to 7.4.
Although the two intakes look quite similar, switching to the Brodix intake had quite an interesting effect on the dyno. Peak torque dropped 9 lb-ft to 676.2, and horsepower dropped by 12. The Brodix intake, however, did exhibit a very flat torque curve, so the average power in the low-speed band only dropped by approximately one for both power and torque. We figure the main culprit here is the interior runner walls for the Brodix intake extend well into the plenum area. This helps create longer runner lengths for better torque production but can also hurt shared plenum volume and signal at the carburetor.

Test 4

Brodix Single-Plane to Edelbrock Victor Jr. Intake
Brodix 345cc Unported Heads: 2020003
Edelbrock Victor Jr. Intake: 2902
HP: 687.1
LB-FT: 684.1
There's a reason why Edelbrock's Victor Jr. intake is an incredibly popular choice in all types of applications: It just works. On the dyno, the Victor Jr. put up the best numbers yet with the Brodix as-cast cylinder heads, punching out 684.1 lb-ft of torque at 687.1 hp.

Test 5

Victor Jr. to Weiand Track Warrior Intake
Brodix 345cc Unported Heads: 2020003
Weiand Track Warrior Intake: 7622
HP: 687.4
LB-FT: 686.2
We've got to say that Weiand's Track Warrior single-plane intake manifold was the surprise of the test. While the peak power number was essentially the same as the Victor Jr., it provided a bit more torque practically all the way through the pull. Average power for the Weiand was about 1.5 lb-ft better than the previously best Victor Jr.

Test 6

Exhaust Lash Change
HP: 676.4
LB-FT: 689.2
We had been looking forward to finally seeing Edelbrock's RPM Air Gap dual-plane intake, but the guys at Prestige had been worrying about whether the Comp solid-roller cam (258/268 duration at 0.050) was too large. Specifically, they felt the exhaust duration was simply too much, so they opened the lash on the exhaust valves from 0.020 to 0.030 inch, while the intakes were left at 0.020.
The additional lash made the exhaust lobe act "smaller"—or as if it had less duration—and that made a big difference very early in the rev range, with an additional 14 lb-ft of torque at 2,500 rpm. That lasted all the way until 4,900 when the engine's need to breath exceeded the shortened exhaust lobe. Since the crew was all about making maximum fun down low, they approved of the change and left the lash at 0.020/0.030 for the rest of the tests with this cam

Test 7

Weiand Track Warrior to Edelbrock RPM Air Gap Intake
Brodix 345cc Unported Heads: 2020003
Edelbrock RPM Air Gap Intake: 7562
HP: 666.0
LB-FT: 702.2
Finally, we get back around to testing the Edelbrock RPM Air Gap dual-plane intake on the as-cast Brodix heads to see how they compare to the Air Gap on the ported heads. On the dyno, this looks like an excellent combo. By the way, this is different from the intake we used on the ported Brodix heads from the initial test, because those heads have an oval intake port and the as-cast heads have rectangular ports.
With the single-plane intakes, the torque peak had always been around 4,600 rpm, but with the dual-plane Air Gap, peak torque crested at 3,800. This test was also the first time peak torque exceeded 700 lb-ft with the as-cast heads. Average torque across the range was about 10 better than all the single-plane intakes, and while the peak horsepower number wasn't as high, the average power across the range was approximately the same.
What's the moral of the story? If bragging about the big horsepower number you pegged on the dyno is your primary concern, stick with the big single-plane intake. But if you want the most possible power in a usable rpm range, a properly designed dual-plane intake can be your friend even on a big-inch big-block.

Test 8

Brodix 345cc As-Cast Heads to Brodix BB-2 Plus Cylinder Heads
Brodix 312cc Unported Heads: 2060002
Edelbrock RPM Air Gap Intake: 7562
HP: 682.0
LB-FT: 684.3
Next up we tested to see if an even smaller port could help torque production. Brodix's BB-2 Plus heads are designed to be an all-purpose head for big-block Chevys. Like the other heads, these have 119cc combustion chambers but smaller 312cc intake runners. There is also a smaller intake valve (2.250-inch versus 2.300) to better match up with the smaller port.
When paired with an Edelbrock Air Gap intake manifold, this combo produced more low-end rpm than the as-cast 345cc heads, but the amount is relatively small and the line mimics the improvement made by increasing the lash on the camshaft earlier. The results, here at least, are inconclusive.

Test 9

Solid to Hydraulic Roller Cam
Comp Solid Roller (Grind #): 4293/4287
Comp Hydraulic Roller (Grind #): 13579/3372
HP: 683.4
LB-FT: 703.7
Until this point, the camshaft was a solid roller from Comp Cams with 258/268 duration at 0.050-inch lift, a 110-degree lobe separation and 0.680/0.681-inch valve lift with 1.7:1 ratio rockers, but the staff at Prestige thought a hydraulic-roller cam with slightly less lift and duration could be a better fit. To find out, they installed one from Comp with 252/258 degrees duration at 0.050 inch, 0.659/0.647 valve lift, and a 112-degree lobe-separation angle.
Typically, with a smaller cam you can expect to move the torque curve lower in the rpm range at the expense of horsepower higher up because the smaller cam simply won't allow the engine to breathe as well at high rpm, but this cam really agreed with the smaller 312cc intake ports on the Brodix BB-2 Plus heads. Not only did the torque jump up from 684 to 703, but the horsepower didn't suffer, either. The power gains under the curve were also significant; average torque improved by 9 lb-ft while horsepower improved by 6. The hydraulic cam almost certainly would be the wrong choice for the high-flow ported Brodix heads, but for these as-cast heads, this cam is just about perfect.

Test 10

Change to Quick Fuel 950-CFM Carb
Quick Fuel 1,050-cfm Carb: RQ-1050
Quick Fuel 950-cfm Carb: RQ-950
HP: 683.2
LB-FT: 703.3
After determining the smaller hydraulic cam was a better match for these heads, we decided to check and see if the same held true for the carburetor. So off came the Quick Fuel Technology 1,050-cfm Race-Q double pumper, and Aitken bolted up a slightly smaller Race-Q version at 950 cfm.
The peak numbers were almost the same, but the averages dropped a bit. Of course, the differences were small, and any time you can run a smaller-cfm carb without harming power too much, you will usually wind up with better throttle response. Overall, we bet the 950 would be the preferred carb on the street.

Test 11

1-Inch Open Spacer vs. No Spacer
HP: 682.8
LB-FT: 700.8
Before calling it a (very late) day, we decided to make one last pull of the handle. This time, we ditched the 1-inch open spacer that had been on top of all the intakes for testing. Removing the spacer cuts down on the intake's plenum volume, which hurt power production to the tune of 3 lb-ft of torque and about 1/2 hp. The lesson learned here is easy: If you've got room for a spacer, run it. But if it is going to require you to cut a hole in your original hood, leave it on the shelf and don't worry about it.

Im going to post some more data in near future of performer rpm vs dart open plenum, vic jrs, weiand team gs. On these mild 502 variations, talking cams similar to hp 500 or smaller, 89 octane , stock heads or entry level 305/310 aluminum heads, theres not even a fair comparison between a open plenum and performer rpm with a spacer in my real world dyno testing. Just took a weiand team G 4150 off a 509 and swapped to a performer rpm, went from making numbers like a 454 should make to what a 502 should ACTUALLY make aside from that particular intake having most horrible distribution out of the box of any open plenum Ive ever dynoed with!

So, are you saying that the Team G's that I put on my Merc 420's that I upgraded to HR 500 EFI cams might be the issue why my Panther slowed down from when I had chinese XS Extreme single plane manifolds (Dart knock offs) flat tappet cams?

Were your weiand team gs worked by Jimmy V or box stock? This customer had a box stock team g with 4150 flange, 1,2 were 17-1 on top, 3,4,5,6 were 10.5 to 11.8/12.0 and 7, 8 were 15.5/16-1 on top. Was at 523 hp/560 tq, edelbrock performer rpm brought that up to 547hp/595 tq but real gain was from 2500 to 5000 where it gained as much as 60 ft lbs and fact it could be jetted to get safe afrs. The Team G needed the plenum dividers heavily worked if I was guessing, compared to a 4500 team G I had here, it looked like they just cast a 4150 flange onto a 4500 team g. That left the 4 barrells favoring the center 4 cylinders, Smitty

Smitty/Articf, you and Rookie are speaking about a 454cid engine---right? With an engine the size of a 454cid, then I would greatly expect that a dual-plane intake manifold such as the RPM Air-Gap dual-plane to perform much better over a single plane in most cases, but NOT in every case.

Back when I bought my used 32' Active Thunder, the original owner dumped a ton of money in the engines. They were 454cid bored .030" over to 461cid and the blocks were "bore notched" so as to un-shroud the valves on a smaller BBC cylinder bore size. These 461cid engines had small solid/mechanical roller cams with Merlin cast iron Oval port heads that had 2.19"/1.88" valves with bowl porting and short side radius work and the same Dart 4150 flange intake manifolds that I ended up using on my 565cid engines.

Anyway, those little 454's (461") made about 619hp @5500-5700rpm and this is with Stellings full length tubular headers installed on the engines in the boat---and I rode in that boat that way before I even knew I was going to buy it---and it was a real runner and I am thinking the Stellings tubular dry exhaust system was maybe why it could run well enough to install single plane intakes (Dart) on those engines back during that time

I also tend to believe that the more CID you have with the Big Block Chevy then the less reliant it is for a dual-plane intake manifold---at least that is how I used to think until I read the Prestige Motorsports article by Jeff Honeycutt with all the dyno testing results---really has me second guessing myself about those dual-plane intake manifolds---especially on a 582cid engine where Honeycutt in Test #1 stated:---- "We don't want to spoil it, but it was the highest output of any of the tests"-----= so now I am back to thinking a dual-plane intake may actually work on a 565cid engine turning only 5600rpm and lower marine application engine , especially on a 582" that they were conducting dyno tests on during that time..

I may have to end up laying down the SMACK for the Air-Gap dual-plane and do my own dyno test compared to the Weiand Track Warrior manifold which i have already bought---which in the test by Prestige looks to have a slight edge over even the Victor Jr. as Honeycutt comments in his article in Test #5----"We've got to say that Weiand's Track Warrior single-plane intake manifold was the surprise of the test"---- .These weren't decisions that I was expecting this time around, but the curiosity is really rattling me.

How about in boat comparison tests ?
Like it sounds Rookie might embark on.
Sometimes the dyno tells one side of the story.