Inlet Skirt Length This is the length of the intake skirt of the piston from the crown edge (or top edge of ring if using an "L" or Dyke's type uppermost ring) to the skirt's bottom center. If the skirt's bottom edge has an inverted "U" or other shaped cutaway, measure to the highest cutaway point up the skirt's center.
Port floor height This is the vertical distance from the top of the cylinder to the lowest point along the floor of the intake port window.
Port roof height This is the vertical distance from the top of the cylinder to the highest point at the roof of the intake port window.
Effective port width This is the average width of the window just inside of the chamfered sides of the intake port 90° to the direction of air flow.
Radius @ top corners This is the average radius that creates the upper corner shapes of the intake port window.
Radius @ bottom corners This is the average radius that creates the lower corner shapes of the intake port window.
Opens @ This is the exact point, in crankshaft degrees of rotation before Top Dead Center, that the intake port window is first cracked open by the rotary disc valve.
Closes @ This is the exact point, in crankshaft degrees of rotation after Top Dead Center, that the intake port window is finally fully closed by the rotary disc valve.
Port ID This is the average port body inside diameter at the window covered and uncovered by the disc valve. When the port is not round, I prefer to calculate and/or measure its' window area and then select a round port ID that has the same area for simulation input.
Radius from crankshaft center to port center
This is the distance from the crankshaft centerline to the disc valve's port window center, as shown in the diagram at right.
Reed thickness The thickness of a reed petal (Item "A" as shown in the diagram below right) ideally determined with a micrometer or vernier caliper.
Reed width The actual measured width of the reed petal only (Item "B" in the diagram at right).
Reed length The measured reed petal length from the reed petal end to its' retaining screw's shank (Item "C" in the diagram at right).
Reed block port width The actual width of the reed block opening beneath the reed petal (Item "D" in the diagram above right).
Reed block port length The actual length of the reed block opening beneath the reed petal (Item "E" in the diagram above right).
Reed block angle This is the total included angle formed between the reed block window openings (Item "F" in the diagram above right).
Length from clamp This is the closest distance measured inside the reed block from the beginning of the reed window opening to the shank of the reed petal retaining screw (Item "G" in the diagram above right).
Stop plate radius (Item "H" in the diagram above right) To measure and calculate, proceed as follows using diagram at right. Remove and lay the reed stop plate on a flat surface upside down. Calculate the rise height "R" by measuring from the flat surface to the highest point of the stop plate's curve on what is now its' top side and subtracting from it the vertically measured stop thickness "VT", as shown. Now measure the chordal width "W" across the curve from edge to edge. Calculate the stop radius using the following formula:
(W² + (4 x R²)) ÷ (8 x R²)
Number of ducts This is the total number of transfer passages in the cylinder and would include main, auxiliary and "boost" type ports.
Avrg. duct length Measure the centerline length of each transfer passage from entry point adjacent to crank flywheel in crankcase to exit window in upper cylinder (as in diagram at right). Add all lengths together and divide by the number of transfer passages to get the average duct length.
Effective duct width This is the true chordal width when measured 90° to the exiting air movement as is illustrated "W" in the diagram at right.
Upsweep angle This is the measured angle upward from
an imaginary line drawn horizontally across the cylinder bore
as shown in the diagram at right. If the port roof is "flat"
with no upward tilt, enter "0" here.
Corner radius This is the average radius that forms the corner portion of a port window at the cylinder wall surface.
Duct roof height This is the vertical distance from the top of the cylinder to the highest point of the roof of a port.
1st pair This refers to the "Main" transfer passages that immediately flank each side of the exhaust port(s). Some vintage model two stroke engines only employed a single pair of "Main" transfer ports.
2nd pair This refers to the "Auxiliary" transfer passages that are adjacent to the "Main" transfers and second away from the exhaust port(s). Sometimes they are referred to by some tuners as the "Secondary" transfers. Many two stroke engines have only the two sets of "Main" and "Auxiliary" transfer passages.
3rd pair When a two stroke cylinder employs a pair of transfer ports in the rear of the cylinder, opposite the exhaust port and adjacent to the "Auxiliary" transfer passages, it is sometimes described as having "Twin Boost" ports. Some Suzuki models and a handful of others utilize this six transfer passage arrangement.
Boost duct This refers to a fairly common transfer passage layout wherein there is a single "Boost" type transfer port located exactly opposite the exhaust passage(s) creating a five transfer port system. In the case of the reed valve type intake design, this "Boost" port is often cut right into the top of the intake window.
Variable Height Exh. Guillotine This would include any type of mechanism designed to alter effective exhaust roof height as engine RPM changes. "Full down" position is the lowest exhaust roof height that this mechanism would provide as measured from the top of the cylinder deck.
Exhaust Down Sweep Angle This is the average angle (in degrees) downward from horizontal that the exhaust passage points as it exits the cylinder bore.
Exhaust Centerline Length This is the average centerline length from the exhaust window at the cylinder bore to the gasket surface plane where the exhaust manifold attaches.
Exhaust Port Outlet ID This is the average inside diameter at the exhaust outlet where the manifold and its' gasket attach. If the outlet is not round, describe it as accurately as possible to allow area to be deduced.
Auxiliary Exhaust Ports These are small "sub" exhaust ports that some manufacturers incorporate flanking left and right of the main exhaust window and above the main transfer windows. They join with the main exhaust passage before the exhaust manifold and assist with upper cylinder scavenging of spent exhaust product.
