Thanks for keeping me honest and looking it up. I tend to pay for a month once a year and binge watch all the episodes and then cancel because I'm a cheap-***.

Adam

 

The duration you are talking about yes. But in terms of absolute duration the valve is lifted, there is zero difference with 1.5 or 1.6 rocker arms. It is a linear multiplication. 1.5 times zero is zero. 1.6 times zero is still zero. The timing of the valve is exactly the same - the only difference is the ramp rate. Once you have lift, there are changes in duration - but they are negligible at low lift and more significant at high lift. No, no one is going to notice or feel a 2 degree difference in duration at .050". You might notice it on a dyno, but no one's butt dyno is that good. As evidenced by the whopping 100 RPM shift in peak power noted by engine masters - no one is noticing that without a dyno.

.006" is not industry standard and it is absolutely not where flow is recognized to have begun or stopped. No idea where you got that, but it is wrong. Industry standard is .050" of lift, because no one was using the same point for their advertised durations. Comp uses .006" - others do not. Flow starts as soon as the valve leaves the seat - by any tiny amount. It stops when the valve is sitting back against the seat. It doesn't wait until .006" of lift. Its not sitting at .005" of lift saying "just you wait - I'm almost going to flow...". That is beyond ridiculous, and coming from a background in mechanical engineering specializing in fluid flows, I can tell you with absolute certainty that it is not how physics works.

There are plenty of intricacies that must be understood when making this change, but the difference in duration is not really one of them. You aren't changing it enough to have any significant impact on idle or low RPM power. Most of this discussion is very much "spherical chickens in a vacuum" - purely academic. The important details about valvetrain geometry and handling the increased loads are getting lost because of this.

 

It also depends what events you're talking about. When I say "valve events" I TEND to think solely of "Intake Valve Open", "Intake Valve Close", "Exhaust Valve Open", "Exhaust Valve Close" -> THOSE events don't change with a change in rocker ratio.
BUT, if your definition of "valve events" extends to things like "intake valve opened to .050", "intake valve opened to .200", "exhaust valve opened to .050", "exhaust valve opened to .400" -- THOSE events WOULD change with a rocker ratio change because the valve is opening and closing faster. The events on the open side at lifts above .000" happen slightly sooner (in crank degrees and actual time with a constant RPM), the events on the closing side of the cam lobes at lifts above .000" happen slightly later. (Just like a car accelerating faster and braking later.) --Just like the Performance Trends valve motion+rocker ratio chart shows.


Adam

 

WOW!

Scott.

 

This has been interesting. I stepped out of this conversation a while ago. But now come back after reading everyone's opinion.
Just to say that I run 1.6 Rockers. Have for many years. Originally installed them back when I still had stock heads and Cam. Just looking for a little more lift out of the factory L82 cam on the cheap. Truthfully it didn't seem to make any difference down low at all. Perhaps a tad bit mid range and up. But it was a inexpensive mod. Never seemed to affect idle vacuum. Never found a down side.
But certainly a lot of opinions on here.

 

As long as the cylinder heads are still flowing good at the additional lift there’s no downside to the 1.6

T&D and Jesel sell all kinds of rocker arms that have ratios between 1.8 , 1.9 and 2.0 providing the cylinder heads support the geometry and many do , LS’s can run those ratios too