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View Full Version : N/A plenum mod, vortex tuning and porting plan...



RoadWarrior222
02-04-2010, 05:23 PM
Hi folks,


Been tossing around an idea for porting my plenum "differently". Not sure this would be such a goer for a turbo plenum, but wanted to do the undone for N/A. Basically everyone says, oh everything's been tried, you don't get much from an N/A, and you look at the builds and mods and everyone did the same old, same old.

What I'm thinking about trying to do, is force the formation of counter rotating vortices in each half of the plenum, that transfer momentum across as valves alternately open each side. Doing this might just be as simple as leaving about half to a third of the plenum divider standing top and bottom.

So, I had my drawing office utilise sophisticated CAD technology to model it for me ...
http://img651.imageshack.us/img651/4295/04plenum.png
... Yeah I was kidding I sketched it in MSpaint.

Top picture shows what I want to happen. Have each side trade air momentum from the bottom to the top as valves open each side. Filleting each side of the divider may help. Need an air path across the middle about the width of the radius of the vortex. I'm going to plan the angles better to keep cross flow across the top to a minimum, while allowing for a 10-11* flow divergence off the fillet on the bottom as the flow switches sides. So the pale blue arrow in the middle would flip direction. Notice this should feed moving air from the top of the plenum down into the runner. This should be better I hope than moving almost dead air round a right angle corner as might happen when it just sucks off the short side. The offset of the runner feeds will contribute to the vortex motion, hopefully establishing it strongly from mid RPM and mid throttle upwards.

Bottom left picture shows sequence of cylinder induction from top. Now, wondering if we could further strengthen vortex, and keep it established by offsetting the filletting so there is some anti-reversion effect, like 1 can't pull back from 2, but as soon as 1 is done 2 can pick up it's "spare" induction momentum. What happens after #6 sucks is a puzzler... will the vortexes try to U bend round, in effect forming one vortex, or will they stay in two columns, and can #6 transfer momentum back up it's own column to #1... still thinking about that, and which way to try biasing it.

To the right was a thought about tripping up the slower air off the bottom of the throttle body with a ski jump to throw it into the crossover area to get pulled in... but if the U vortex formed it would be the top TB flow that needed angling down, because it would be rotating outward at the top and inward at the bottom.

Now, flow biasing that tends to "switch" when one side sees less pressure than the other, might be accomplished by having a nice curved short side into the plenum from the entrance. This is because air tends to nail itself down to a curved surface. The yellow shows where this might be hacked out, if enough material available, the red where it might be built up if it isn't. Think half a donut stuck round the intake. This might also be enhanced by a couple of short stub vanes in the roof of the plenum. If done with a kind of fat nosed airfoil section, it would be more angle insensitive, like a fat round edged wing is less stall sensitive on an aircraft, and flow will take a cue from pressure differential according to which valve is open.


Anyway, what I think could be accomplished here is preserving intake momentum, lengthening intake path, keeping velocity high and not continually stop-starting and stalling, feeding the runners from the top more to stop them having to suck around a right angle, and maybe charge packing and ram charging from the momentum. Depends how strong it gets at WOT and higher RPM. Should be good for torque, shooting for a torquey "area under the curve" build, top end is hard to use with an auto.


That's it in brief,

RW222