There are two forms of "lobe center" talked about. One is the angle formed between the inlet and exhaust cam lobes, and the one that I use, is the inlet valve fully open position, in relation to the crankshaft position.
This has more meaning that just the relationship of the inlet and exhaust lobes, to each other, which is just the result of positioning the two individual cam positions.
The main objective of timing the inlet cam is to match the maximum open position of the inlet valve to the maximum air speed in the inlet tract. The fully open position of the inlet valve is fixed by the gearing. The maximum air speed in the inlet tract varies with the engine speed. The maximum piston speed is achieved at about 85* ATDC. At say 1000 rpm the maximum air speed will follow the piston, but as the engine speed increases the maximum air speed lags behind the piston speed. So that at say, 5000 rpm the maximum piston speed is at 85* ATDC, but the maximum air speed will not happen till say 115* ATDC.
So to get the engine to develop maximum torque at 5000 rpm we have to have the inlet valve fully open, at 115*to allow the maximum air speed to match the fully open valve position. As we change the engine speed for maximum torque, we have to change the inlet lobe center to bring the two to the same speed. Move the torque peak up the rev range requires the lobe center to be retarded. Bring the torque down the range needs the lobe center to be advanced.
The duration used, is a function of the engine speed that the maximum torque is required. The higher the engine speed, the longer the duration needed to allow the cylinder to fill.
This outlines the 3 stages that I purposed, some time ago.
http://www.subaru-svx.net/forum/show...ghlight=stages post 164.
Thanks for joining the thread Matt.
Harvey.
