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Porting is the process of modifying the shape of a port (tube, pipe,
etc...) in order to control the fluid (air) that is moving through it.
Flow and velocity are mapped over a cross section of the port in several
areas. The port is then modified to get the desired port flow and velocity
with a laminar flow. Turbulence, swirl, and port stability are measured to ensure the port is working efficiently.
F.A.Q.'s
A.
Improve the efficiency of the port(s).
B. Port Modification.
A. What is a flow bench
for?
-
Incorrect Port Shape
- If a port is not shaped correctly, flow through the port may be distorted.
-
This would be similar to putting your thumb half way over the end of a
garden hose on high. The water still comes out of the hose, but volume
could be reduced, velocity increases on one side, and decreases on the
other side.
This is fine, but if you are trying to fill up a 5 gal bucket with water, it
will take forever.
- This is similar to having an incorrectly shaped port; where
the air/fuel trying to get into the combustion chamber is moving fast
on one side, but takes a long time to get all the air/fuel inside.
Port Surface
- If the port surface is rough or has large casting lines, these irregularities
can cause turbulence in the air going through the port.
- It is similar to taking a nice smooth river and throwing rocks,
boulders, and tree logs in the middle to make it a class five
rapids.
-
Direction & Flow
- Having an efficient port is going to help get the fluid
through the port,
but where is it going? How many ports are there? When do
they open and close?
- Take two garden hoses and start to fill up a five gallon
buck (cylinder). Also, punch a small hole in the bottom of the
bucket on one side for the water to run out (exhaust). If you
aim the two garden hoses (intake ports) at the small hole (exhaust),
most of the water will go right out of the bucket. Aim the two
garden hoses at the sides of the bucket in different directions and
the water will swirl around in the bottom of the buck a few times
before it trickles out the exhaust hole.
- Where the port(s) are aimed depends on the number of intake
and exhaust ports, where they are located, how the combustion chamber
is shaped, the design of the exhaust system, 2 stroke vs. 4 stroke,
etc...
Volume & Velocity
- The larger the diameter of the port, the higher the volume and
the slower the velocity.
- This is similar to turning the hose faucet on full and using a
1/4" hose or a 5/8" hose.
The 1/4 hose shoots a small stream of water a long distance.
Whereas the 5/8" hose puts out a lot of water at a slower velocity.
- The volume/velocity design for each port depends on the direction of
the ports and the design of the engine.
Timing
- The key to making an engine produce the most amount of power
is having the greatest amount of air/fuel in the combustion chamber
when the fuel is ignited.
- All the parts of an engine need to be matched, so the
air/fuel mixture is at the correct place at the correct time.
Balancing
- Engines with more than 1 cylinder can produce more power if
the engine is balanced. On a four cylinder engine, it is better
to have 4 cylinders running at 95% efficiency, than 2 cylinders
running at 100% and 2 running at 90%.
It is similar to jogging with one tennis shoe on the left foot and a
work boot on the right foot.
(note: we actually work on getting all 4 cylinders to run at
100%)
- Matching all the ports between all the cylinders will help
to balance the motor and produce more consistent power.
Rider/Pilot
- Tuning an engine to produce peak horse power between 13,000 and 14,000
rpm can be uncontrollable for a rider who rides between 10k and 14k rpm,
and useless for a rider who runs the engine between 4k-10k rpm.
- Tuning an engine to produce a lot of torque between 4k-6k rpm and
horsepower between 10k-14k causes a lull between 6k-10k rpm and makes
the bike more difficult to ride.
- Porting, modifications should fit the rider/pilot. The goal of modifying
anything is to make it more useable for you, the
rider/pilot. Modifications should make the rider/pilot & bike
go faster; not just the bike.
-
A flow bench is a testing unit to check the flow of fluids. It
assists in checking the flow rate in a port and at any location in that
port. It produces information like in the picture below.
This information can than be used to detect problems,
increase the performance of the current design, make changes in the
design, etc...
The real technique to porting lies in the ability to know
what the port design should be, for all the variables in the motor, and
using a flow bench to see if the ports are changed accordingly.
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