Camshafts, idle quality, driveability and LSA-REAL WORLD EXP and OPINION
Hmmmm.... what is new about LSA effecting idle? Look at all the torque and low RPM cams ever ground..... 112 or 114 LSA.
As far as cubes versus LSA, I am surprised to hear this. /6 and 360 and 440 cams all get ground on the same basic LSA's and all react the same way to LSA changes. As well as Chevvies, Fords, Opels, etc....
Real world experience? I had a low duration, high lift 114 LSA cam in a 351C that passed all emissions except NOx, idled like stock but would beat factory 440 GTX's in B bodies all day long. Torker manifold (gasp!) and 1-7/8" (gasp again!) and it still idled with 18-19" of vaccum. The lift and the heads made it breathe so duration and overlap could be sacrificed and idle improved.
Not sure I understand this statement; is it talking about reversion during intake closure on the compression stroke? How can that contaminate the intake with exhaust?
If the intake valve is still open, and the port can't overcome the upward movement of the piston, you get reversion. That reversion is where you get the dead rich idle you can't clean up.
Did you mean to say "If the intake valve is already open..."?
This is going into a different topic, but just an observation: I would not put too much faith in flow bench numbers revealing what will truly happen with reversion and during overlap. Flow benches are steady state tests, and real operations are anything BUT steady state; real operating flow is start-stop-start-stop ad infintum, and the air mass in the intake has to be accelerated from a dead stop each and every time. The MASS of AF mix in the intake tract (heads and intake up to the plenum) IMHO dictates a that behavior more (and perhaps much more) that low lift steady state flow. As well as compression ratio, which effects suction pressure as well as compression pressure, and also impacts total cylinder clearing of spent gases. (Another topic.... I'm out of control! LOL)
