340 dyno chart thoughts
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.
Advertised duration was created to be just that. An advertisement. Many many moons ago, guys would advertise their cams in catalogues and magazines. But there was no standard as to how things were measured. Like you mentioned, now there is. But guess where it came from? Advertisements. It forced all cam companies to measure the same way for advertisments, so guys couldn't claim more duration but not mention they were measuring it differently than their competitor. It's really that simple.
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!
Not confused. I'm just right. You obviously don't understand valve events. How do you calculate duration? You use valve events. How do you calculate valve events? By measuring the cam. How do you calculate LSA? You use valve events. How do you calculate valve events? Once again, by measuring the cam. Valve events are GROUND INTO THE CAM. They happen at the same point on the cam NO MATTER WHAT. The only way to change them, is to regrind the cam. Even if the cam is installed advanced or retarded, those valves STILL open and close at the same time relative to each other. Can you figure out valve events with out knowing the duration? Yes. Can you figure out the duration without knowing the valve events? No. So guess which determines which.
And no, duration, LSA, advance, etc etc, don't tell you EVERYTHING about valve timing events. They give you a good estimate of how that cam will perform. But obviously they don't tell you everything. Hence why a cam with the same duration, same lift, same LSA - can have different valve events and different drivability.
I really don't know how else to explain that to you.
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?
I don't care about flow. I care about events. Hence I put them on the same playing field.
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!
And if you don't know valve events, can you determine duration? No. Valve events determine duration. Without knowing valve events, you don't know duration. Therefore duration does not influence valve events. Duration is a product of how long that certain valve event is occurring. No valve event? No duration.
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.
Uhhhh right from the manufacturer. So, you're wrong.
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.
Once again. This is why I calculated them both at .006. To reduce it right down to almost base circle. To get the FULL valve event. This is what DCR calculators use to find out DCR. Hence this is why I use it. And yes. I understand they are measured differently. Hence why I calculate them both at .006. To get the full angle. I don't know how else to explain that to you but I can't understand it for you.