stroked small blocks in the race cars?

[blykins]

Originally Posted by MAStuart

Ok dont know if this will help at all. If 2 cams were identical except for separation angle. And installed on the same intake center line. The one with the narrower separation angle would open the intake at the same time as the wide one. But it would have more overlap and a later ex opening. The narrower one would also have more valve closed time during the compression and power stroke.

The overlap is what you have to keep an eye on. It can make or break an engine.

1. Overlap can make/break vacuum, which is necessary for accessories like power brakes.

2. You can have too much overlap (either by narrow LSA or by large advertised durations) which will push the charge right out the exhaust instead of using it for power-making. That's why engines with really large or tight LSA cams sound so radical at idle, they are inefficient.

3. Overlap can be your friend on a large intake port, such as in the case of a 4V 351C head or a Tunnel Port FE head. With the valves open at the same time, the exhaust can scavenge the intake charge on a port which is otherwise too large and too slow on velocity, which will help fill the cylinders.