Norm Peterson

As long as you remain carbureted, stick with the dual-plane. You'll be operating for hours at a time in the ~3000 rpm range, but only a few seconds at a time north of 6000. I think the torque curves for single and dual plane manifolds tend to cross at 5000 rpm or a little more, so you need to be pulling past 6000 to get the revs in the next gear up near that. Race car territory.

If you were going to modify a carb manifold for EFI of some sort, it's different, and you should start with a single plane manifold for a DD in that one specific situation.


Norm

Norm Peterson

You almost certainly need to rework the carb a bit, sort of in the direction that you'd go for a single plane manifold but not quite as far.

You may be able to have an aluminum plate welded in to put all (or maybe not quite all) of the original divider height back. I'll even bet that it's possible to slot the manifold so that you could try various divider plates with different amounts cut down.


Norm

P Zero

Are you guys thinking of the Victor Jr. as the single plane? Victor Jr's should ONLY be put on REALLY built motors. Definitely not a mild one. If anyone says its ok then theyre idiots and have no business giving advice.

Ive run both. The dual plane does make more power off idle. But the dual planes tend to die off around 5000. As for a single planes, if you get a med rise, the off idle power kinda sucks, but it comes on strong at around 1800 and pulls hard up to 7000. Its kind of a trade off, but selecting an intake will really depend on HOW you drive. If you tend to get on it often and keep it above 2000rpm a single plane should do you just fine. If you just kind of putz around then a dual plane is the way you want to go.
-P.

Norm Peterson

Even the Torker or Weiand IMCA manifolds are aimed a little higher up the rpm scale than you'll normally use in daily driving. I doubt that the Torker runners are as good as those of the Performer RPMs (link) or overall any more than slightly better than the Performers, as it (and similar single-plane manifolds) is of considerably older design.

As the basis for an EFI, the Victor Jr may not be all that bad, since fuel atomization and maintainingcomparable air:fuel ratios across all cylindersis not as dependent on vacuum and velocity conditions in the plenum.


Norm

JMD

http://www.popularhotrodding.com/tec...ld/index1.html

Insome recent issues of Popular hot Rodding, they featured a 408 build from a 351W. In their final dyno runs they ran a comparison between a single plane and a dual plane. The single plane was a Victor Jr., and the dual plane wasan RPM Air Gap. The single plane manifold go a 950 cfm carb where the dual plane only had a 750 cfm, so the run is not exactly "apples to apples" but the article hints that a bigger carb can be run on a single plane manifold than should be run on a dual plane.

The single plane did noticeably raise the HP and torque and it also shifted the power-band upa fewhundred RPM across the board until engine speed approached 6,000 RPM. The dual plane did not start giving up until 5,900 RPM at 527 HP....The single plain test topped out at about 6,000 RPMat 551 HP.

I think the specific engine build was more inviting to the single plane than most street engine buildswould be, and I believe that the dual plane equipped engine would be more streetable as indicated from the HP & Torque charts in the article.

P Zero

Another thing I forgot to mention, single plane manifolds have noticably better throttle response.
-P.

urban_cowboy

I planon buying both a Victor Jr. and Air Gap and tring them both without changing cam and carb. EVERYONE I have talked to about my Dart engine tells me to run the Air Gap. My specs are 450-475hp peaking at about 6000 with plenty of torque from 2500 up. I want it when I need it on the street and will do a little bracket racing, but never plan to spin her above 5000 for long periods as in circle track racing. After telling three or four engine gurus that, they all said Air Gap on the street and Victor Jr. on the track. The Holley/Weiand and RPM intakes never cam up in conversation.

67mustang302

The Air Gap is the RPM, just with a slightly larger plenum and a minor cutdown in the divider. Dual planes can still make good high rpm power for street engines(high rpm being in the 6,000-7,000 range). It's always a tradeoff though, do you want better bottom end, strong mid-range or better top end. A lot of people under estimate the power potential of dual plane intakes and jump straight at a Victor series intake. Overall power band is what really matters, and not peak. With an engine turning 6,000rpm a single plane might make more peak hp, but a dual plane might make more power most everywhere else in the higher usable rpm range(4,000-6,000) such that the dual plane creates more average power rather than more peak, and ends up making the car faster than a single plane would. Most of the advertised rpm ranges on the intakes are the range in which they work BEST, not necessarily just work. That's why guys with RPM's are making good power at 7,000rpm, or someone like me with a 5,500rpm intake that still pulls like mad well past 6,000rpm. Total average power in the usable rpm range is what matters though, peak power is only nice on paper for bragging.

The thing with single planes is that you're using twice as many barrels to draw the same amount of air through as with a dual plane(a dual plane has any given cylinder drawing it's induction pulse off of only 2 barrels, whereas a single draws from all 4, same air volume through twice as much opening). That means that the venturi velocity is lower and metering strength is reduced, which often necessitates the running of a SMALLER carburetor with a single plane intake than a dual. You still have to get enough velocity through the carb to generate good metering signal, otherwise you have no fuel sheer at the booster, and atomisation and vaporization gets reduced, and power along with it. That means it's also dependant upon both the amount of air the engine can draw, and the fuel delivery and sheering capability of the carburetor. A crappy carburetor with a single plane on a stock engine is just going to rob power everywhere. A stroker engine though that breathes heavy in a low geared car, with a carb that sheers well may benefit from a single plane. It all comes down to build.

Just don't underestimate the power producing capability of a dual plane. Many people see them as a street rather than a race/performance intake simply because they're "smaller" or operate in a "smaller rpm range." It's the same pervasive "bigger is better" mentality that's been around forever. In reality there's quite a bit of complex physics invloved that has a very dynamic effect on how everything works. If you have 2 intakes, A and B, and B is bigger, but the engine flows less than what A is capable of, swapping A for B just loses power, since the induction velocity drops, manifold vacuum along with it, which reduces metering signal, and as a result, atomisation and vaporization go away, and so does power. If the combination is limited by the cam/heads, putting a bigger intake on isn't going to increase the engine's airflow. The chain is only as strong as the weakest link.

I often see guys at the track with supposedly"weaker" engines, running dual planes on engines that put out less power(peak power anyway). But they're running just as fast as other guys with similar setups but more powerful engines with larger single plane intakes, larger heads, larger cams etc. You're much better off trying to squeeze every last drop of power out of a smaller setup, than you are trying to FIND power in a larger setup. ESPECIALLY in a car that's driven regularly on the street.