lobe separation angle
Pick a cam, any wide LDA cam.
When you tighten up the LDA of that same cam, You will be closing the intake earlier.
The overlap difference will be exactly double the LDA change and;If you put them both in exactly at split overlap,the ICA will be exactly 1/2 the overlap difference.
By tightening up the LDA you will be getting an earlier closing intake valve(and more Dcr), and a longer power extraction cycle, and as a consequence; more overlap.
More power extraction is not always better, unless you are going for gas mileage. Most of the work of the expanding gas is done by 90 to 100 degrees ATDC
More overlap is not always a good thing either, especially with log manifolds. But with tuned headers, this period can be exploited.
Lets pick a pair of 276/284 cams, one is 114, and the other is 108.
Lets start with the 114 cam. To put it in at split overlap requires an installed centerline of 112. Then the Intake will close at 70*ABDC, leaving 110* for compression.Power extraction will be 102*. And overlap will be 52degrees.
Next, lets check the 108LDA. To put it in at split overlap, requires an installed centerline of 106*.The intake will close at 64*ABDC, leaving 116* for compression. Power extraction will be 108*, and overlap will be 64 degrees.
Let's say you have a 30over-teener with a true 10.0 Scr. According to the Wallace Calculator;
The 114 cam, in at 112, will make a 7.58 Dcr@ 148 cranking compression.
The 108 cam, in at 106, will make a 7.96 Dcr@158 cranking psi
Running characteristics are mentioned above.It is my opinion that as specific power increases on those narrow-LDA cams,the powerband decreases; meaning they become more sensitive to what tranny runs behind them, and what rear gear it is stuck with.Maybe sensitive is the wrong word. The power comes on later and harder. So if you are stuck with bad gearing, the power delivery won't really start until you are way speeding. This is probably not a concern for most streeters with typical street cams.
I can tell you from experience that the 292/508/108 cam likes plenty of rear gear to get going, and likes at least a 4 speed, or if an auto, likes plenty of TC.In my combo it kinda exploded at 5500 and carried on to past 7000. So that was a 1500 rpm powerband.But with 3.55s it didn't start until 64mph. See what I mean?
Now the Hughes 230*/110LDA cam I currently have, is very similar to that 276/284 cam. The engine has a totally different character. The powerband seems to start at 3500 to 4000, but it is incredibly long and flat. I can't really feel it come on, like I did the Purple.At first I was very disappointed.But after some retuning, it's kinda nice putting the hammer down at 3500/41mph, and lighting up the 295s. I kinda miss the nasty 292 idle tho....
Now here's the kicker; the 292,in at 104 has an ICA of 70*ABDC, which would be the same as the above 276/114 cam, and just 6* later than the current 276/110 cam. The rest of that duration was moved into the overlap period.Totally different character.The idle vacuum was quite a bit lower, and the peak-vacuum rpm was quite a bit higher. I don't recall the numbers anymore, but estimating, I would say the 292 idled 3 to 4 inches lower and vacuum-peaked 500 to 600rpm higher.No biggy,a little more gear for the 292, and a little more clutch, and away it went. Then when it hit 5000, hang on! Then, keep it on the pipe...