LSA* not LAS... damn autocorrect..

 

Opening and closing events are needed along with more duration numbers.

 

A little skeptical here as I am scratching my head wondering why you would be using some pretty good size durations with such low lift numbers? What engine spec. are these cams going in and as someone above said, what are the rest of the cam specs. These cams seem strange?

 

That is lobe lift, not total lift if that's what you were thinking. The second one is currently in my 533" 12 degree bbc on gas, single 4 on a tunnel ram. The other came out of a 632" 12 degree bbc on alcohol, tunnel ram with an injector hat. I dont have the rest of the numbers with me but I'll get and post them

 

Subscribing as well to this. I am really interested in how the decision is made on where you want duration to be on a high effort N/A build to promote more of the ram affect on cylinder filling???

 

Duration is simply the amount of time (in degrees of rotation) the lifter is up off the base... or therotically the valve is off its seat. So if increase exhaust duration, that means you are keeping the valve open longer. Things effect this like lash and valvetrain deflection on the opening and closing ramps.

Lobe Seperation Angle is a stupid measurement (IMO) that dosent tell you anything useful. Simply put if you take the Intake Centerline add it to the Exhaust Centerline and divide the sum by 2 you will get the LSA. It dosent control anything. It dosent effect anything. Its just a number... a byproduct of physically having both the Intake and Exhaust lobes on the same stick.

Centerlines... both Intake and Exhaust are very simple points of reference. They are the highest point of lift on each lobe. Where they occur is expressed in degrees of rotation.

So to your questions about what does what... just one point of reference cant tell you anything. Like in the case of LSA.... You need the ICL and LSA or the ICL and ECL to know if the cam is straight up or advanced or retarded. What its altering is what is really important to the engine. The valve events - When the Intake Opens and Closes.... when the Exhaust Opens and Closes. When both the Intake and Exhaust are both Open (Overlap). When both valves are closed....

There is so much more than numbers on a cam card.... those are reference points that you can measure to ensure the cam is ground and installed as the mfgr intended. Thats all they are.

If we were to discuss the important stuff like what are the effects of closing the Intake at 76* vs 67* or having 50* of overlap vs 20* of overlap... or even simply moving the overlap peroid 4* from its current point.... There is a books worth of discussion in every single degree of possible change to each one of those events.
Will

 

If we were to discuss the important stuff like what are the effects of closing the Intake at 76* vs 67* or having 50* of overlap vs 20* of overlap... or even simply moving the overlap peroid 4* from its current point.... There is a books worth of discussion in every single degree of possible change to each one of those events.
Will

This is what I to read more about.

 

Those numbers are good to have for reference, but they are really just derivatives of the valve events that you'll choose for cam selection. You can have 2 cams both with 288 degrees of duration that will have 2 completely different power curves depending on what the valve events are.

 

The cam events @ 0.050" are
28/80 94/42 70 degrees overlap
29/79 88/38 67 degrees overlap


Stan

 

There ya go.

2 intakes with very close events but 2 ex with 6* different openings, with 3* less overlap.

Could maybe a cam guy tell us what that would do in maybe 2 different apps..... Says 10:1 head limited pump gas street engine vs 14:1 high rpm race engine?

 

Harold would talk for days with you, he loved cam theory, and they each have their own theory.

 

Go to speedtalk and search Harold's posts. You'll have weeks worth of info to read.

 

There is a thread or two in here with George Bryce on this topic. Good reading and info about

 

I've found this to be reasonably good theory on valve events.

https://www.mechadyne-int.com/app/u.../the-impact-of-variable-valve-actuation-on-engine-performance-and-emissions.pdf

 

Use cam #1 on 632 nitrous motor and cam #2 would work decent on 632 NA motor