An interesting thing about single carb single planes, with a traditional firing order the outer runners fire in sequence 7-2-1-8 followed by the inners 4-3-6-5, many/most Edelbrock manifolds are designed with a more or less centered plenum and others like this M1 and the team G have more of a "maltese Cross" type plenum where the front and rear outer cylinders "share" a v shaped passage before splitting to 2 seperate clyinders. 4-3 and 6-5 fire consecutively as well but they are across the plenum from one another and 8 and 7 actually fire 270 degrees apart.

Any theories on what the benefits/drawbacks to each may be? I have seen where consecutive firing cylinders (2-1 and 5-7 Particularly) can result in the earlier firing hole "stealing" some charge from the later, I can see where the maltese cross might help the 5-7 but not the 2-1.

The easiest to understand 'in theory' would be the Indy dominator style where the blades of each of the four venturis actually pass over the center divider between 2 runners so the fuel is more directly "channelled" to the ports.

Being that any given intake valve is closed far more than 1/2 the time (even with a very large cam) it's interesting to try to visualize how the dead-headed pulse in one runner (when the intake closes) effects the (wet i.e., fuel laden) flow to the one that is (or is just about to) open....

you pretty much answered your own question(s) i think. I would add that putting in fuel damns on the plenium
floor would help a great deal. jmo what about dampening intake resonance, which affects hi-rpm horsepower. any thoughts?

Would this just be "nature of the beast"and one of the reasons they invented sequential multi port fuel injection?I see no way around robbing effects to the cylinders you pointed out.Would wide open throttle disperse the air and fuel more efficiently?

Well if I answered my own question I must not be smart enough to understand what I "solved"

I always looked at a single plane's objective to maximize VE by effectively "charging" (or at least getting as close as possible) the plenum within an targeted optimum powerband range. You see this goes more to an "all ports drawing from the same well" theory like the old torker/Tarantula design. but what designers found was if the mixture moves too fast fuel separates, particularly on the inside ports where you form an acute angle in the stream on the way to the valve. This is in large part why most modern racing engines have non-siamese ports and port entries as close to identical as possible. The next step was the curved runner that allows all ports to enter the head perpendicular to the valve first seen in mopar land) in the Street dominator and later in the M1. If the plenum is "charged", theoretically all the ports should see close to equal charge from the plenum...barring any port to port variances/restrictions on the way to the valve. For maximum power the motor really wants the air to "fall" into it, (atmospheric)....that is if it can't be "pushed" (i.e., supercharged or overlap "ram" effect).

Not looking to 'smoke anybodies motherboard' here, I was really just hoping some might share their knowledge and understanding of the VOODOO of intake manifold design and theory so we can all learn (and possibly unlearn) a little more. Really just thinking out loud and having a bit of fun trying to get an interesting topic going.

SW,
i think that modern single plane intakes are as good as its gonna get, if your looking to improve on that,
then your really gonna need some VOODOO science to try and figure that one out. not saying it can't be done.
BUT there is already a very good "hybred" intake manifold out there that maximizes the VE and handles fuel distribution very effectly, even on
relativly stock engines. i'll let you think about what that is for a while. anyways on my previous question that i posed..
what about dampening intake resonance, which affects hi-rpm horsepower. any thoughts? my MB needs a good smoking LOL.

You know even as a 16 yr old kid (many moons ago) I though the SP2P principal might work very well for high RPM if its runner cross section could be scaled WAY UP

Intake resonance to the best of my knowledge is "addressed" by tapering the runner smaller as it approaches the valve which allows the pressure wave to slow slightly on it's way back to the plenum....the issue with single planes (as said) is they are really optimized for a specific runner/engine size over a fairly narrow target range. In my minds eye a reflected pulse of air just acts like a wall in the plenum which I suppose effectively reduces plenum volume by that amount for just that instance.

my brain is starting to hurt

Sick topic Wize I am interested and trying to learn! What does VE stand for?

VE is volumetric efficiency....it's basically the volume of air/fuel Consumed verses (divided by) it's mechanical displacement and expressed in percent, 105% is very good, 78%....not so much. VE typically (mathematically) peaks at the RPM peak torque is produced....the trick is to try to keep it as high as possible (more accurately or fall the slowest) past the peak torque RPM for as many RPM as possible...that's the key to making horsepower, pretty much regardless of displacement the 'law' is the same.

I like this thread, but feel that my science background can only compromise years of engineering experience. Since "tuned" exhaust systems are a measurement of the speed of sound/ given volume to length of the exhaust phase of the engine stroke, it would appear to me that the same "concept" should be applied to the intake side as well. Unfortunately with carburetion, the wet phase of the intake would limit the effective runner length based on the adhesive properties of gasoline to the surrounding walls. I have crept around some of the "concepts" on this board and have garnered interest in the port velocity of the intake. This is my basis of motivation: Boyle's law states that pressure and volume are inversly proportionate, so for a given volume of gas that you want to move at the negative pressure (should be a "relative" constant barring the obvious friction coefficient) provided on the down stroke, you either, lower total volume (of the intake side) or taper the diameter of the orifice (assumed the "throat/valve"- there are volumes on effective collars to increase the speed of mass) to increase the velocity of the charge. I have been looking at my M1 manifold for a few weeks (haven't started porting it yet) to see what is obvious to change the flow into the cylinder head and your concern of the negative pressures within the intake has vexed me so far. I would assume that the "negative pressures" within the intake runners do affect the others during the different cycles, but would require eight "running" measurements to understand the affects on each runner. Fundamentally, it would appear that the effect of the intake pulses are negligeable between the others runners, but given the average enthusiast power levels, engineering costs would be prohibative. I could say that in professional racing that the individual runners are ported differently to equalize intake strain between the ports, but I am sure it is either secretive, or above most enthusiasts level of interest. I would probably suggest a tapered intake to the port diameter to maximize the velocity, but again, the power increases would be negligeable due to the shape of the intake port.

Bobby you're just thinking too darn much, you guys are going to give me a headache. it's been 15 years since i was required to study the mechanics of fluids but imho anything done with an automotive engine is going to be a compromise with a hord of variables. most (myself included) do refer to VE but in reality it's actually mass efficiency that is under consideration. there are so many things that affect cylinder filling inertia being one of them that's directly affected by charge velocity. i would think given the equipment, engineers and research that's been done on the newer manifolds by the manufactures they should have come pretty close to optimum given the constraints of production, dimensions, performance considerations and cost.

As I understand it...

Ports are tapered to keep the air speed constant from the plenum to the valve. The friction loss robs energy from the moving air. If the port isn't tapered, the air will slow. Since it takes energy to speed/slow air, the more constant you can keep the velocity gradient through the intake tract, the higher inertial force it will have when it gets to the valve.

Also, too much speed is a bad thing. This is because the vacuum signal can only travel at the speed of sound. When the port speed is too fast, the vacuum signal from the valve (piston down stroke) travels too slow back up the port.

This is what really happens when a port "chokes" at high RPM/small cross section...

most intakes plenum volume is too small because it is a comprimise for hood clearance

Hey this kind of stuff can be fun every once in a while, right?

Thanks for the great responses!

wanna know what the ultimate single plain intake manifold is???
the Performer RPM.

i like threads like this too. keeps that 1 brain cell i have left stimulated.

This whole mess is why the realy high specific out put motors in the world are ALL individual runners. They have no "stealing" from each other and the sky is the plenum.

Jeffrey is that you?

Oh yeah the IR also does incredible things for idle quality, think about a motor cycle that turns 14,000 rpm but idles all day real smooth at 1000 RPM imagine the idle a big block would have to have if it could turn 14,000 rpm Put a properly tuned IR manifold on there and it will smooth out real nice. Adding the plenum was just a way of feeding 8 cylinders out of 2 or 4 venturi or if the 2X4 carbs were too small. A plenum would give a place for the mix to flow into when the valve was not open thus it could be smaller because it could be fooled into flowing 100% of the time instead of just the %25 of time the valve was open. If you were to run 2 1000 cfm dominators on an IR manifold they could be tuned to run a stock 360 perfectly because each venturi flows about what one port does but put a plenum in there and it is super duper over kill and bog city. I think this is part of the reason the HotHeads early Hemi could do so well in the latest engine masters contest (that and those guys really know there early hemis ).

An intake manifold is tuned to a certain RPM like an exhaust system is. A dual plane has longer overall runners for lower rpm. When the valve closes the rebounding pulses take a certain amount of time to come back into the plenum and at a certain RPM can help with a "ram effect" into the next runner that is drawing on it. But, it's an RPM thing. A single plane uses much shorter runners so it takes less time for that pulse to make it into the common plenum so it helps ram air at a higher RPM. A tunnel ram can make a great torque manifold if hood clearance isn't an issue and the runners are kept small, but it also makes a great HP manifold due to the ability to have a carb barrel over each cylinder's intake runner and the ability to tune the runner to the RPM and having such a great shot into the head port.
As with everything, it's all a tradeoff. Runner length, plenum volume, runner height, type of fuel, required volume of fuel, etc.
Firing order also throws a wrench in the workings. I like the 4-7 2-3 swap. It seems to me that it'd make the least mess of things in the intake manifold.
I think most manifolds have their places. Within reason.

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.