340 dyno chart thoughts
I did read your post. and i do get what you're trying to say. modern lobe design has a faster rate. ie more duration @ 0.050" relative to seat/advertised duration.
This is fantastic for getting lots of performance, but it doesn't change the fact that more duration @ 0.050 will still affect your idle vacuum. (everything else being equal)
Let me show you a picture i quickly made up which demonstrates this in an easy to understand visual way. The shaded area is valve overlap.
Note how Both camshafts have 60 degrees of overlap @ seat duration (each graph is 60 deg wide).
Also note the where horizontal 0.050" line intersects with the RED closing of the exhaust valve, and then again with the BLUE opening of the intake valve line. these intersections are 10 degrees apart on the first camshaft and 30 degrees apart on the second.
The shaded area is overlap. As you can see, even though both of these cams have "60 degrees" overlap according to advertised duration numbers... the second camshaft has a crapload more valve lift during that entire 60 degrees. This increases the effect of overlap and reduces idle vacuum. Any questions?
I did read your post. and i do get what you're trying to say. modern lobe design has a faster rate. ie more duration @ 0.050" relative to seat/advertised duration.
This is fantastic for getting lots of performance, but it doesn't change the fact that more duration @ 0.050 will still affect your idle vacuum. (everything else being equal)
Let me show you a picture i quickly made up which demonstrates this in an easy to understand visual way. The shaded area is valve overlap.
Note how Both camshafts have 60 degrees of overlap @ seat duration (each graph is 60 deg wide).
Also note the where horizontal 0.050" line intersects with the RED closing of the exhaust valve, and then again with the BLUE opening of the intake valve line. these intersections are 10 degrees apart on the first camshaft and 30 degrees apart on the second.
The shaded area is overlap. As you can see, even though both of these cams have "60 degrees" overlap according to advertised duration numbers... the second camshaft has a crapload more valve lift during that entire 60 degrees. This increases the effect of overlap and reduces idle vacuum. Any questions?
