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Tuned Exhausts for 2-strokes
adapted from  "The two-stroke tuners handbook"
 

Note: Dimensions are in inches! All diameters are inside diameters. LT, L3 and L1 are measured from the cylinder wall, not from the exhaust flange!  LT= (Eo * Vs)/N Where  LT = tuned length in inches  Eo = Exhaust open period in degrees  Vs = sonic wave speed (use 1700 ft/sec)  N = Crankshaft speed, in RPM D1 = stock lead-in pipe dia. D2 = SQR( 6.25  *  D1 * D1 ) D3 = D1 * 0.62 L3 = D1 * 10 L7 = D3 * 12 L2 = (D2/2)*cot(A2) L1 = LT - (L2/2) L4 = ( (D2 - D1)/2 ) * cot(A1) L5 = L1 - ( L3 + L4 ) L6 = ( ( D2 - D3 )/2 ) * cot(A2) A1 = half diffuser-cone angle of divergence   (see below) A2 = half baffle-cones angle of convergence (see below) Notes:  Centreline length of curved pipe:   L=R*0.01745*angle of bend The 2 stroke book says  because of testing,  an 8 degree angle of divergence for the diffuser cone connected to the lead in pipe is the minimum angle to start with and 20 degrees for the compression cone at the other end of the pipe is a good starting point. Solo 210 N=6300  Eo=180 LT=48.57 D1= 1.44  D2= 3.6  D3=0.89  L7=10.7  L3=14.4 L2=10.2 L1=43.5 L4=15.44 L5=13.63 L6=7.68 A1=4 degrees A2=10 degrees Useful cotangents (degrees) cot 3.0 = 19.0811  cot 5.5 = 10.3854  cot 8.0  = 7.11537  cot 11.0 = 5.14455 cot 3.5 = 16.3499  cot 6.0 = 9.51436  cot 8.50 = 6.69116  cot 12.0 = 4.70463 cot 4.0 = 14.3007  cot 6.5 = 8.77689  cot 9.00 = 6.31375  cot 13.0 = 4.33148 cot 4.5 = 12.7062  cot 7.0 = 8.14435  cot 9.50 = 5.97576  cot 14.0 = 4.01078 cot 5.0 = 11.4301  cot 7.5 = 7.59575  cot 10.0 = 5.67128  cot 15.0 = 3.73205