He cut mine on a 107LSA and told me too it was good for efi which was contrary to all the research I have done as well. I have been wondering about this because I plan to either jump back into my old Pro Flo system or into a new throttle body system.
Keep in mind the 4 stroke cycle event: intake-combustion-power-exhaust, repeat.
Keeping your exhaust and intake lobe as well as all other cam parameters the same; Lobe Seperation Angle is the distance of the exhaust lobe center point from the intake lobe center point measured in degrees around the cam's base circle. The LSA rotates the exhaust lobe either closer or further away in reference to its corresponding intake lobe. A numerically lower number like 107 degrees means the lobes' center lines or "peaks" are closer together and referred to as "tighter" or "narrow" where as a numerically higher LSA of say 116 degrees means the lobe center lines are further apart in reference to one another and referred to as "loose" or "wide".
What LSA controls or allows is a certain amount of over lap of the valves during the cylinder's intake event. Remember during the intake stroke the exhaust valve is on the closing side of the cam lobe while the intake valve is on the opening side of its cam lobe. A narrower LSA will have more valve overlap which means the exhaust valve will still be slightly open for a period of time through the intake event where as a wider LSA will allow less overlap which means the exhaust valve will not be open for as long while the intake is open.
Remember in naturally aspirated applications the incoming fuel during the intake stroke is relying solely on vacuum created by the downward drawing piston. Having the exhaust valve still slightly open during the intake stroke creates a scavenging effect within the cylinder because the spent gases escaping through exhaust valve help draw in the new intake fuel charge thus fill the cylinder more. This also allows some of the new intake charge to escape out the exhaust valve and that is what you here in the exhaust pipe when you are running a rowdier cam shaft.. the bumpity bump good stuff!
Now in reference to efi and camshaft profile, I'm still not positive on the science. I am guessing that since efi is introducing fuel into the air stream under higher pressures than carburation the cylinder doesn't need as much scavenging help and by closing the exhaust valve sooner the cylinder retains the charge, and has less blow by which makes tuning efi easier??
Looks like I better get another cup of coffee and study some more.
