Autopneumo-Controlled Variable Runner Induction (long)

[DAW]

So I'm designing this and I wonder if anyone has done a similar design?

Basically a two stage induction system with a few key features: for L6 application, paired small diameter runners are grouped according to ignition intervals, i.e., 1&6, 2&5, 3&4.

Each pair (all 6 runners are equal length) joins briefly at a small plenum to which a small SU is attached, sans throttle rod and plate (rod holes capped). SU piston spring set low tension, quick response. Each of the three pairs configured same so 3 SUs (small, like 1 1/4" or smaller), without throttle plates. Each airhorn side has a flexible air intake hose joining to a plenum which has mounted to it a large throttle body/air filter. Also attached to this main plenum via flexible air hose, is a large, single (maybe double later) SU serving the log-type plenum immediately near the cyl head, with short runners which each "Y" connect to the long, primary, runners. The single SU is a large unit fitted with an emissions-type piston weight, a strong piston spring, and a rich needle. This SU also has the throttle plate and rod removed and ends sealed.

Operation: One throttle plate is actuated by accelerator, low speed airflow can't lift heavy secondary SU piston so the secondary/short ram system isn't activated until high progressive engine speed. Low speed airflow is, however, well balanced due to ignition interval match-up, and charge speed is optimal. High charge speed enhances fuel atomization, and produces great torque and responsiveness. The key to this system is that the same factors that allow the primary system to respond quickly (column/pressure-effect), become limiting (flow-restricted by small diameter SUs and long, narrow runners), such that the primary system becomes effectively, a pneumatic plug that the engine can't move as R.P.M. increases. However, as that occurs, the engine can move/decrease another plug which activates the secondary system: the large SU serving the short ram/runners manifold. So, the 3 small SUs are pegged open now and heavy duty, high flow tasks are via this large SU (or two, maybe) augmenting the wide-open primary; and all are in response to the accelerator pedal. When power/rpm falls off, like on a hill, the secondary system automatically cuts itself back (as its heavy piston is the first to fall when airflow drops); which puts acceleration back into the high-torque/lower-flow primary system, just where it needs to be to get the rpm back up.

SU calibration is done by needle choice, piston spring choice, and size of primary SUs used, with respect to tuning for primary/secondary transistion at given R.P.M. (different for rally vs road vs autocross).

So, for those waiting for a tri-SU set-up on the Nissan L6, here it is plus one or two more SUs to boot.

DAW

[Guest John Adkins]

Offenhauser made a line of intake manifolds called "Dual Port". These were manifolds designed so that the primary barrels of a carburetor fed small diameter intake runners and the secondary barrels fed larger diameter runners. The small diameter runner and the larger diameter runner for each cylinder stacked stacked on top of each other. I remember they made these for most domestic V8s. They made them for the 2.3L pinto engine.... I wonder if the make one for the Nissan L24/L28? if they do, maybe you could modify one for your project?

 

[ July 10, 2001: Message edited by: John Adkins ]

[DAW]

The latest generation cars are pulling more horsepower and torque by incorporating variable intake manifolds. Most have a regulator valve of some sort which directs induction charge from long runner for low end torque to short runner for high end flow/horsepower. This system uses internal control valves (SU suction pistons) to accomplish the same thing but more simply/directly. This design began with an attempt to build a tri-SU L6 and evolved from there. I have many of the pieces for the prototype and it does not depend on a cast aluminum manifold. I'll post pics when it's ready.

DAW

[Guest Anonymous]

One of the first places I remember seeing it wasn't in a car, but a bike. The Yamaha Vmax put uses a variable runner design of some sort that really makes power at 6k, it comes in with a wallop and pray your pointed straight. It It puts out something to the order of 125+ hp out of 1.2 litres of V4 engine. The short of it is, properly designed the variable runner scheme's do work.

 

Regards,

 

Lone

[randy 77zt]

ford uses 2 intake runners per cylinder on 3.8 and 4.2 v6-f150,windstars,v6 mustangs.plus the cobra dohc 4.6 v8.the runners have throttle blades on a common shaft.operated by a vacuem diaphram and a solonoid controlled by ecm.

[DAW]

Honda, Mazda, Toyota, etc all have a variable runner system in some form on some of their performance vehicles, including SUVs. The design I'm describing accomplishes the same end result, but I believe possibly in a smoother, simpler fashion that is directly meshed with the load demands of the engine so that it creates the "type" of power curve needed by the vehicle at any given driving condition.

The fact that the SU is a carburetor is incidental to some extent. The needles could be removed, main jet plugged, fuel bowl removed, etc and a fuel injection/engine mgmt system (for fuel delivery at the intake port) added to dispense fuel. What the SUs are being used for is their airflow regulatory properties. The feature of the SU which makes it such an elegant, self-contained, induction modulator in the first place is being expanded upon in this variable-intake design. Instead of throttle plates, solenoids, and vacuum diaphrams, this design directly uses the engine's own flow to maximize/tailor...it's own flow.

If one were to suck on two straws in a glass of water simultaneously and one straw is twice the diameter of the other, The smaller straw would have the liquid up to you much faster, responsively; than the big straw. However, with a big pull, the small straw would hit some limit of how much liquid it could supply, while the big straw (although not quick) can deliver huge amounts of liquid flow. Changes in suction at this high flow state effect almost entirely the large straw side because the small straw has become, essentially, a fixed orfice/resistance value. We're just applying the fluid characteristics of air to do the same thing the water would.

DAW