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.