dmcca

1st November 2011, 22:21

So ive got some questions about Engmod2T... hopefully there are other users on KB that can help, and maybe we can create a bit of a database of info to share. The program seems very powerful but i sometimes wonder if im feeding in accurate data or if im getting things a little wrong... without a dyno at hand its very hard to be certain.

When modelling a reed cage that has an internal divider or stuffer before the reed petals, do you subtract the area of the divider from the area of entrance to the reed cage when calculating the 'diameter of the rubber block' (entered in the Inlet Port window)?

The photo below shows what im talking about...

http://i553.photobucket.com/albums/jj373/dmcca/DSC08431.jpg

The rubber intake boot is on the right, the reed cage is on the left.

The rectangular area at the exit of the rubber boot is calculated and entered as the last diameter of the intake pipe (basically modelled as the cylinder side of the carb). In this case the area is 1190mm^2 which equates to an equivalent diameter of 38.9mm. This is entered in the Inlet Type window.

When you then go to the Inlet Port window to model the reed cage itself it asks for the 'diameter of rubber block'... this is essentially the area at the entrance to the reed cage but do i just enter the same value of 38.9mm diameter or remove the equivalent area (in direction of flow) of the divider from this figure??... in this case the divider is 8.5mm x 39.7mm = 337.45mm^2, so the total area of the reed entrance becomes 1190-337.45 = 852.55mm^2 or equivalent diameter of 32.5mm

The graph below shows a KTM200 modelled with the above reed cage, black line is a "diameter of rubber block" value of 32.5mm (divider removed from total area), red line is a "diameter of rubber block" value of 38.9mm (divider ignored). Obviously taking the divider into account looks better, but which one is actually correct???

http://i553.photobucket.com/albums/jj373/dmcca/ktm200graph.jpg

To complicate things further, in this case the divider protrudes from the reed cage by about 10mm, so when its bolted to the rubber intake it technically changes the final area of the intake pipe just before it ends... should i actually be removing the area of the divider from the last stage of the cylinder side carb pipe instead of from the entrance to the reed cage???

When modelling a reed cage that has an internal divider or stuffer before the reed petals, do you subtract the area of the divider from the area of entrance to the reed cage when calculating the 'diameter of the rubber block' (entered in the Inlet Port window)?

The photo below shows what im talking about...

http://i553.photobucket.com/albums/jj373/dmcca/DSC08431.jpg

The rubber intake boot is on the right, the reed cage is on the left.

The rectangular area at the exit of the rubber boot is calculated and entered as the last diameter of the intake pipe (basically modelled as the cylinder side of the carb). In this case the area is 1190mm^2 which equates to an equivalent diameter of 38.9mm. This is entered in the Inlet Type window.

When you then go to the Inlet Port window to model the reed cage itself it asks for the 'diameter of rubber block'... this is essentially the area at the entrance to the reed cage but do i just enter the same value of 38.9mm diameter or remove the equivalent area (in direction of flow) of the divider from this figure??... in this case the divider is 8.5mm x 39.7mm = 337.45mm^2, so the total area of the reed entrance becomes 1190-337.45 = 852.55mm^2 or equivalent diameter of 32.5mm

The graph below shows a KTM200 modelled with the above reed cage, black line is a "diameter of rubber block" value of 32.5mm (divider removed from total area), red line is a "diameter of rubber block" value of 38.9mm (divider ignored). Obviously taking the divider into account looks better, but which one is actually correct???

http://i553.photobucket.com/albums/jj373/dmcca/ktm200graph.jpg

To complicate things further, in this case the divider protrudes from the reed cage by about 10mm, so when its bolted to the rubber intake it technically changes the final area of the intake pipe just before it ends... should i actually be removing the area of the divider from the last stage of the cylinder side carb pipe instead of from the entrance to the reed cage???