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