I was thinking about the tolrances allowed in the valve tolerances, and I had a couple of questions that some others might be able to help me answer. First, doesn't an aftermarket cam just increase the size of lobes and/or duration. And second, if they increase the size of the lobe meaning that the valve stays open longer, couldn't the same thing be done by increasing the shim size to the bigger of the tolerances allowed, or maybe even go a couple (thousandths, mm, or whatever it is) higher? Would this increase in duration cause the vavle to stay open longer, which would increase the amount of airflow in and out of the engine, in order to make maybe even a few extra horses. I don't know the HP increase in the new cam, but would the bigger shims be able to do something similar?

The problem comes when the valvle is closed. If you shim the valve up it WILL give you more lift, but when it is closed it will never fully close and seat fully. This will cause the valve to quickly burn and the motor will need many $$$ after that.

If you want more cam you need a bigger cam and will have to still use the factory valve clearances.

Derek A
90 535i