When dealing with an ever varying intake valve opening (following a lobe) and a cylinder that has a non linear rate of acceleration from TDC to BDC...not to mention varying cylinder Pressure thoughout the RPM band....how can the flow through a port EVER BE CONSTANT?

Since it came up....I wonder what does anyone who understands the concept think of the large SP2P idea? Not as a race manifold (where a single is still king despite some runner to runner flow balance issues) basically as a conventional 180 degree dual plane with LARGE (VICTOR SIZED) independent runners to a divided plenum, this would give an extremely broad power curve and should flow better at high RPM than a conventional shared runner dual plane. The SP2P was designed way too small for low compression stock motors seeking high velocities at low speeds, it's a good idea it just runs out of steam (velocities get too high) to early in the powerband for a higher RPM application.

Probably the only way to balance pulses in a single plane intake (other than an independent runner) is probably a 180 degree crank, as someone said the drawbacks of conventional designs are too small to worry about and the all out race (Comp eliminator and Pro stock as examples) manifolds are scienced out to the 'Nth' degree for that specific application.

I thik indy makes a sort of big port version of an SP2P for a big block. It is suposed to be a pretty good manifold fom what I have heard.

I think there is no firing order possible where 2 ports don't breathe one after the other in siamese fashion. Like you said the 180 crank is the only way. I think the plenum type manifold is just a way to save money on carbs and there are better ways to do it except they are expensive. Even for a $ no object motor like a pro stocker you would still have to develop all new HUGE carbs to run 8 inividual runners.

there is such a thing as a venturi collar in typical engines,, its called the pushrod pinch..

dual planes have many runner lengths to have a broad tq curve and typically smaller ports to aid air speed at lower depressions/engine speeds to gain better throttle response.

a typical tunnel ram for a race motor is tuned somewhat like an ind runner manifold by trying to position the carbs so that the throttle bores line up to the runner openings so you get throttle bore pressure to exact a force on the runner to complement the inertia force already in it, for better cylinder filling in the compression stroke. you also get a better signal to the venturi/booster so throttle response is gained but typically those motors are designed/intake port size'd to make hp and tq very high, which hurts throttle response.

when you have extended runner dividers in a single plane manifold you have something similiar to the tunnel ram, you get thrott

there is such a thing as a venturi collar in typical engines,, its called the pushrod pinch..

dual planes have many runner lengths to have a broad tq curve and typically smaller ports to aid air speed at lower depressions/engine speeds to gain better throttle response.

a typical tunnel ram for a race motor is tuned somewhat like an ind runner manifold by trying to position the carbs so that the throttle bores line up to the runner openings so you get throttle bore pressure to exact a force on the runner to complement the inertia force already in it, for better cylinder filling in the compression stroke. you also get a better signal to the venturi/booster so throttle response is gained but typically those motors are designed/intake port size'd to make hp and tq very high, which hurts throttle response.

when you have extended runner dividers in a single plane manifold you have something similiar to the tunnel ram, you get throttle bore pressure to act on the runner speciffically, not just the plenum, aiding to add inertia force at all engine speeds, though its not much. you also by lengthening the divider wall extend the column/runner so that you gain more force on the cylinder with the incomming charge at the tail end of filling in the comp stroke.

Thanks jeff, that's very good and valuable input

example with my smallblock. no other changes other the swapping intakes:

w/ MoPar M1 Single plane:
596hp @ 6500rpm
556ft-lbs @ 5000rpm

w/ Edelbrock Performer RPM Dual Plane:
590hp @ 6000rpm
568ft-lbs @ 5000rpm

i think in this case the Performer RPM was the better intake choise IMO. I'll take the 6hp loss and 12ft-lbs (the whole curve was simular)
gain with 500 less peak rpm. this was with a smallish hydraulic roller cam and a holley 950hp carb. street engine.
it might be better the other way around with a bracket engine.

There's really no way to make the charge completely ignore a vacuum signal from the adjacent port in a pair (2,1; 5,7). As velocity goes up and the divider wall gets longer the effect will decay but not to zero.
This means, in a practical sense, that this is not really 8 identical cylinders but instead 3 different classes as to intake port characteristics:
1. "neutral", more or less getting the same charge mass as other Class 1: #3, 4, 6, 8.

2. "leading" cylinders of a siamese & sequential firing pair: #2 and 5, which have their vacuum reduced as their trailing partners' valves open.

3. "trailing" cylinders of a siamese & sequential firing pair: #1 and 7, which have their intakes open too early and disturb their partners, but otherwise appear to function like Class 1.

The adjustment, so far only tested and published on the Mini (B.M.C. "A" Series) L4 by Vizard, is done by increasing the LSA and retarding the entire intake event on #1 and 7.
Doesn't this whack these? Yes, but the net result is positive. The loss on #1 and 7 is less than the gain on 2 and 5.
How much? Perhaps 2-3 degrees LSA.
The Mini intervals are very different. I suspect some Chevy L6 tuners have done this, but aren't talking.

Poly,

So by that logic the "Maltese Cross" arrangement is perhaps an effort to minimize the effects of sequential firing? That's what I thought was the difference in approach.

See how the V between 1 and 2 and 7-8 is quite narrow at the bottom while wider at the top so I suppose the sum of the area (haven't calc 'ed it yet) needs to be larger area than the 2 rectangular intake ports it feeds. A standard Max wedge port is 2.6 x 1.3 so in this case it needs to be larger than 6.76". Just Eyeballing it it is about 3.5" across and the top (allowing for the curved roof) and 1.25" at the bottom so with 3.25" high walls that's roughly 7.7 square inches so that's about 14% more cross section than the sum of the 2 ports that "window" feeds. Again it reminds me a bit of the Team G except the G has absolutely NO FLOOR at all, it's an inverted V.

Also regarding your write-up.... on a traditional single plane I'm having trouble understanding the 1-7 correlation as they are on the opposing sides of the plenum and 180 crank degrees apart in firing.

tell me if im wrong,, bolt the manifold to the head and tell me if the port cross section at the flange when you look it as a planer slice through the total runner still looks like the size of a max wedge.

you cannot say that the manifold is 14% larger than the runner it feeds,, the runner is in the plenum and ends at the valve, the engine does not know where the manifold and head separate and it doesnt matter. look at an fe,, look at a hemi,, then a bb mopar,, if you look at the area at the flange and you then think you have some sort of relation you are dead wrong, the intake tract is area dependant on length, and the location of that area with respect to the valve as far as distance away from it.

i talked to larry morgan awhile ago when i did a set of heads for him and i had him list all the things he thought were wrong with the pro stock hemi as compared to a gm,, he said lack of tq,, so i said,, well your intake manifold has a longer runner,, right??? he said no,, well a 99hemi has a .5inch shorter runner in the head than a gm motor,,,, so they were building manifolds which would result with an intake tract .5 shorter than they thought... and they were putting the same area at the flange that their previous gm motors had, and was making the volume of the port the same,,, forgetting that the length was different... so they had a larger port,, and a shorter total runner,,, hence lower tq

the head flange is just the place where the manifold unbolts...

Jeff, hey there big guy, Really the only thing I was referring to/pointing out was the V area that feeds both outbord runners calculates to only ~14% larger than the sum of the 2 runners nominal Max Wedge cross section...in other words, all the air that passes to both of those runners/ports HAS TO pass through (or...is LIMITED TO) that V area in order to get there..., isn't that correct? compared to an old Torker/TM7 (for example) where all the runners lead directly to the ENTIRE plenum, it must be a completely different flow theory. That's the only thing I was pointing out, that's what I'm trying to get my head around....nothing about the runners themselves.

I agree that the flange mating surface is just that...the true intake 'runner' is the entire length from the valve to the plenum.

Great topic. I'm a long way intake guru (or any type of guru for that matter) but like to learn so if you don't mind I'll tag on. Here's a pic of the intake plenum on my Torker II. I noticed it has longer dividers between ports 2 & 4 and 5 & 7 which I assume are an attempt to negate the effect of sequential firing. I'm putting together a mild 408 (approx. 475 hp) and plan on testing it and an RPM to see what works best for my application. After seeing the results Ghost posted, which I was surprised by considering his is making nearly 600 hp and still liked the dual plane, I imagine I'll see similar results if not more profound in favor of the RPM.