340 dyno chart thoughts
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.
When i say "more duration", most people can understand that this will "Open both the intake and exhaust several degrees earlier and close them several degrees later"
Just as they understand that "wider lobe separation" means "open and close the exhaust several degrees earlier and open and close the intake several degrees later".
As for the word "advertised" in "advertised duration". That actually gives a manufacturer license to use any arbitary lift value to spec their cam in degrees of duration. But typically it's SAE, which is 0.006" for a hydraulic cam and 0,020" for a solid..
If you don't believe me about the 0.020 duration being less than 0.006. by all means, purchase a solid camshaft and dial it up on some V-blocks. I'll guarantee that the duration they advertised you will be at a lift of 0.020" and whatever duration you are able to measure at 0.006" will be much greater.
The reason why there is SAE standards for measuring duration is that it's important for a customer to be able to compare one manufacturer's camshaft specs to another's without it being a "250 degrees from brand X is about the same as 240 from brand Y" type deal.
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.
You seem largely confused by this so I'll spell it out for you. duration, lobe separation and installed advance determine the valve events, not the other way around.
These three numbers tell us EVERYTHING about the valve timing events.
More duration is worse because it causes a later exhaust closing and/or an earlier intake opening (depending on whether the duration is greater on just one or both lobes). Since these events overlap. (they creatively called this "overlap"!)
PS, "more overlap" is also easier to say!
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.
again, how much flow do you think a valve is capable of when it is open 0.006"?
How much flow do you think a valve is capable of when it is open 0.050"?
If you think one flows crap-nothing and the other flows quite a bit, Don't you think maybe overlap is going to have a bigger effect at the lift value where the valve flows quite a bit compared to the one flowing crap-nothing?
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.
mmk, You DO realise that duration is a measurement of how many degrees of crankshaft rotation the cam is keeping the valve open for. right? Hence, duration is a major influence on valve events. You can't look at one and not be looking at the other. You may as well be telling me to stop looking at the floods and concentrate on the water!
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.
Where did you get these figures from?
The intake closing angle for a 250/254 - 108 LSA is 53 ATDC
The intake closing angle for 230/236 - 110 LSA is 45 ATDC.
Also, again, the solid cam will have less duration @ the valve on both the intake and exhaust because 10-12 degrees will be taken up by lash.
If they give an advertised duration it will be at 0.020" giving a lower duration figure relative to 0.050"
Let me try to explain it another way.
0.020" is closer to 0.050" than 0.006" is to 0.050"
Therefore the duration specs at 0.020" are going to be closer to the specs at 0.050 than the 0.006 specs will be.
This isn't a faster ramp rate, this is measuring the ramp rate two different ways.
Again, on the hydraulic cam when lobe is opening the lifter moves, the pushrod moves, the rockers move and the valve moves.
On a solid cam, the lifter moves, the pushrod moves. the rocker moves, but the valve doesn't move until the other end of the rocker arm has moved enough to take up the lash, whatever that number is. about 0.020 or somewhere in that ballpark. The lash is taken up and THEN the valve moves. ie the valve moves a lot later than the lifter.
The same is true when a valve closes, it happens earlier than the lifter. Together, they eat about 10-12 degrees. there's just no getting around this.
That is why they're measured differently. I can explain it for you but I can't understand it for you.
