340 dyno chart thoughts

frosty_the_punk said
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?

View attachment 1714997120

So you're agreeing with me then? Or maybe you didn't understand what I'm trying to say. I have no idea why you keep using advertised duration, when I use valve events. Advertised duration is just that an ADVERTISEMENT.

As I said. Valve events determine idle quality. Not duration. Not LSA. Yes, generally with more duration idle is worse. And with tighter LSA idle is worst. BUT that's because of valve events, they determine idle. Period. Part of my point with that, is that as cam technology got better, you could have larger duration with better idle because of improved valve events.

frosty_the_punk said
There's a very simple explanation for this.

By my calculations. if the STL5054AS-8 camshaft is 60 degrees overlap on 108 LSA with 250/254 @ 0.050" as you mentioned, that means it must be 274/278 advertised duration (i couldn't find them listed on their webpage).

So you probably think that the hughes cam is way faster ramp rate than the comp cam, right?

Hughes, 278/282 advertised duration, 250/254 @ 0.050"
Comp, 274/278 advertised duration 230/236 @ 0.050"

Not so fast.

The hughes STL5054AS-8 camshaft is a solid cam, the COMP XE274H is a hydraulic.

The standard for measuring Solid cams is 0.020" for advertised duration.
The standard for measuring Hydraulic cams is 0.006" for advertised duration.

if you get a camshaft, ANY camshaft.. and measure it's duration by both these specs. you will have more degrees at 0.006" compared to 0.020".

In the example you gave, it has little to do with how aggressive the lobe is and is almost entirely because of the difference between how each one is being measured in a different way.

Well the overlap on the solid was 66.

And I use intake valve closing angle at zero (ok well .006") to find overlap. Because that's how you should do it. Yes, I calculated that on the hughes cam.

So once again, my point is that valve events are what you need to look at. Not advertised duration. Because that's an ADVERTISEMENT.

STOP focusing on advertised duration. And start focusing on WHEN the valves actually open and close.

yellow rose said
The next biggest killer, and just as important is the INTAKE VALVE CLOSING point. The later you close the intake , the shittier the idle and the lower the vacuum is. This is the number ONE killer of all things guys ***** about.

This was exactly my point. To bring up the cams I mentioned before?

Hughes STL5054AS-8 250/254 -108ºLSA - Intake valve closing angle 64.
Comp XE274H - 230/236 - 110 LSA - Intake valve closing angle 63.

Which just proves that you can have a crazy big duration, but still have mild valve events. Pay attention to valve events. They tell you what the cam is doing and when it's doing it.