Neracar Port Timing

Neracar Model B Port Layout

2.500" Bore x 2.875" Stroke

The diagram below is obtained by inserting a roll of paper into the cylinder and making and impression of the ports. I then verified the widths and heights by measuring directly.

The exhaust port is in the center, with the transfer divided into two on either side (when rolled, the two left and right edges of the transfers will meet in one port cutout). 

Neracar Model B Port Duration	2.500" B x 2.875" S
Exhaust Port Duration (Inputs in Red)	Inch
R = Stroke	2.875
L = Con rod length	5.740
C = Deck clearance (dist piston is below cylinder top)	0.000
E = Distance from top of exhaust port to cylinder top	2.000
X = R/2 + L + C - E	5.178
Port open = Acos ((X^2 + (R/2)^2 - L^2 )/ (R * X))
Acos	-0.2737387945
=	1.848074493
Convert radians to degrees	105.8868686			Degrees
Exhaust port open duration in degrees =	148		Port Open ATDC	105.9
Exhaust port height	1.250
Exhaust port width	0.875
Transfer Port Duration (Inputs in Red)	mm
R = Stroke	2.875
L = Con rod length	5.740
C = Deck clearance (dist piston is below top of cylinder)	0.000
S = Piston deflector step height	0.050	This parameter is applicable only to Transfer timing calculations on engines which have a step cut into the top side of the piston, forming a deflector to the transfer charge. The value required is the maximum vertical distance from the perimeter of the piston crown to the bottom of the deflector step. Omit the parameter, or set it to zero for pistons with no step—including pistons fitted with a deflector baffle on the piston crown.
T = Distance from top of transfer port to cylinder top	2.250
X= R/2 + L + C - T - S	4.878
Port open duration = Acos ((X^2 + (R/2)^2 - L^2 )/ (R * X))
Acos	-0.5056893901
=	2.100977198
Convert radians to degrees	120.3771263	Blowdown		Degrees
Transfer port open duration in degrees =	119	29	Port Open ATDC	120.4
Transfer port height	0.625
Transfer port width	1.250
Transfer port crankcase entry height	0.750
Transfer port crankcase entry width	1.250
Inlet Port Duration (Inputs in Red)	mm
R = Stroke	2.875
L = Con rod length	5.740
C = Deck clearance (dist piston is below top of cylinder)	0.000
I = Distance from cylinder top to bottom of inlet port	3.625
P = Length of piston on inlet side (bottom to crown)	3.020	????
X = R/2 + L + C + P - I	6.572
Port open duration = Acos ((X^2 + (R/2)^2 - L^2 )/ (R * X))
Acos	0.6515118288
=	0.8612207725
Convert radians to degrees	49.3443155			Degrees
Inlet port open duration in degrees =	99		Port Open ABDC	130.7
Inlet port height	0.625
Inlet port top width	1.250
Inlet port bottom width	1.188