Metric Mechanic - Surface Turbulance |
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| Surface
Turbulence™ Unmasked |
In August of 1988, Surface Turbulence became
standard on all Metric Mechanic engines. By using Surface Turbulence
we've been able to lean out the engine and burn much of the wasted (emissions)
fuel. This has also reduced the fuel input into the engine by 10 - 15%
under moderate (part throttle) driving conditions and up to 25 - 30%
under full load (wide open throttle). Surface Turbulence in an internal
combustion engine is generated by causing a rhythmic tumbling action
over a surface or object. This tumbling, set in motion by a surface
turbulence generator, accomplishes the following:
- It re-homogenizes the fuel and air.
- It reduces laminar flow.
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| Surface
Turbulence Explained |
Surface Air Flow
As air moves over a smooth surface, the thin layer of air having direct
contact with the surface is nearly dormant (barely moving). Why? This
layer is clinging because of surface tension. The clinging is disrupted
by any increase of movement created in that first layer. Movement in
the successive layers is enhanced since they are then "riding"
on an already rolling foundation.
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Smooth Surface
Air flowing over a rough surface is greatest simply because the air
contacts “touch" the entire surface and this causes maximum
resistance. |
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Rough Surface
Air flowing over a rough surface "touches" mainly the high points.
This sets up a stumbling action at the surface disrupting the dormant
layer and generating a slight flow increase. |
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Sculpted Surface
A sculpted surface is one with a repetitive pattern specifically designed
to generate rhythmic air turbulence at its surface for maximum air flow.
It's the basis for the Surface Turbulence in our Engines and Heads. |
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| HiFlo
ST Intake Valve |
| Controlled turbulence can enhance airflow.
This happens because turbulence helps eliminate the "boundary layer",
the dormant layer of air in direct contact with the valve's surface. To
create this turbulence, we machined a series of concentric grooves on
the backside of the intake valve. By way of trial and error, we altered
the size, shape and number of grooves until we came up with an optimal
flow increase. The grooves "stair step" up the valve head like
small ramps. This changes the characteristics of the boundary layer as
it flows over the intake valve. Instead of air dragging, it now tumbles
over the surface of the valve - like a layer of tiny spinning ball bearings.
Over such a surface, the main stream can now move at full speed. Also,
as air flows over these ramps, the fuel mixture hits the backside of the
valve and is kept homogeneous by the tumbling that the grooves generate.
Having fewer heavy particles, the homogeneous mixture burns more completely.
So, the effect is that the "boundary layer" which is normally
lost in airflow with a conventional valve, now has an airflow gain of
2% - 4% by using the HiFlo ST Valve. |
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| Removing
Fuel Particle from the HiFlo ST Intake Valve |
| On a conventional intake valve, as fuel leaves
the fuel injector or the discharge Venturi of the carburetor, it is atomized
into the "main stream." This mixture is either taken into the
cylinder through the opening created by the valve and the seat, or the
mixture runs into the backside of the valve. Fuel hitting the backside
of the valve is then knocked out of suspension. Because the air flowing
over the face of the valve is moving so slowly, fuel particles tend to
adhere to the valve's surface. Eventually there are sufficient fuel particles
collected on the valve to grow heavy enough to be shaken off the valve,
due to a beating action against the seat. Or they get swept off by the
"main stream". Since these heavy fuel particles aren't very
combustible, they're wasted in part! |
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| The
Hi Turbulence Combustion Chamber |
| Inside the conventional combustion chamber,
quite a bit of the fuel mixture runs into the walls and the top of the
piston. Again - these fuel particles will not be very combustible. On
a HiFlo ST combustion chamber, we've generated surface turbulence by using
a recessed dimple to homogenize the fuel. On the combustion chamber side
of the intake valve, we've cut circular grooves. When the piston comes
up for compression, the intake valve acts as a deflector shield and directs
a high turbulence mixture towards the spark plug. This very homogeneous
mixture becomes the foundation for building a strong flame front which
is necessary for a smooth even burn-off in the combustion chamber. |
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