Quote:
Originally Posted by George Miller
If some one shorten the road where you live and there were 10 house in lets say a mile. They shorten it to 3/4 of a mile. You could still have ten house in the 3/4 mile but they would be closer to gather. Now you might get to hear that loud neighbor better. Same with a cam, but some thing had to change. the time the valve is open, how far it opens, how fast you open it, how long it stays open, and so on. There is no free lunch, some one had to pay.
|
There is a problem with that analogy. The road is measured from one end to the other (one mile). The cam lift is measured from the center of the shaft to the top of the lobe minus the measurement from the center of the shaft to the heel or the end opposite the lobe.
You can shorten one and then shorten the other and still have the same lift. The "free lunch" you speak of in a reground cam is the length of the push rod or in our case the valve stem has to be longer because the "road is shorter.
By using the formula (Center of shaft to tip of of the nose) - (center of shaft to the bottom or heel)= lift. Take off from the top and then the same from the bottom and the lift is the same.
Duration does not "start" until the valve is 0.05" off the seat and is measured until the valve is 0.05" from the seat.
I noticed that no information from re-grinder I can find on the net, say they grind the same profile. The do say the same specs.
So what exactly is called out in the specs of a cam, I have only heard of two here lift, and duration?