Design and Simulation of Two Stroke Engines

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Chapter 6 - Empirical Assistance for the Designer
1 25 cc RACING ENGINE
BORE, STROKE, & ROD
54, 54, & 105 mm
PORT OPENS 812ATDC
41 mm WIDE, 12mm rad
TRANSFER PORT OPENS 1 1 42atdc
4 ports, 15 mm WIDE, 3mm rad
INLET PORT OPENS 982btdc
35 mm WIDE, 10mm rad
PISTON ATTDC
Fig. 6.7 Computer-generated picture of 125 Grand Prix engine cylinder.
Those who wish to use this equation should note that the units are strictly SI, and that the
area, A, is in m 2 and Vsv in m 3 . By sheer coincidence, you can enter the value of A in mm 2
and Vsv in cm 3 and the units are self-correcting to s/m.
The data required to perform such a calculation are the physical geometry of the piston,
connecting rod and crankshaft and the timings, widths and corner radii of the porting for the
engine, as in Fig. 5.1(a). Those data are sufficient to produce Fig. 6.1, Fig. 6.2 and Fig. 6.7 by
a computer program, which is demonstrably in command of all of the necessary information.
If the porting is more complex, as in Fig. 5.1(b), then the calculation can be conducted in
stages for each port segment to sum up to the total values. To assist with the deduction of
specific time area values for proposed or existing engines, a computer program is referred to
in the Appendix Listing of Computer Programs as Prog.6.3, TIME-AREAS. The data insertion
format is similar in style to others in the series. The program output is in the form of
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