Cam LSA and advance questions..... [Large cams]
09-29-2003, 12:48 PM
#1
Cam LSA and advance questions..... [Large cams] Say 2 large camshafts (we'll use the G5X2, 232* I, 240* E), one on a 112 lsa and one on a 114 lsa. How much more "lope" would the 112 have vs the 114? Its still a pretty big cam, but would the 114 smooth it out alot, or not that much?
Also, when a cam spec (LSA) is given as 112 + 4 or 114 + 4, I know that means that 4 degrees of advance is ground into the cam. Practically speaking, what does that do? Does it affect idle, rpm peak, P to V clearance, etc? Or does it just have to do with the valvetrain events (valves opening and closing at a certain point)?
I guess what I'm asking is what would be the practical differences between a G5X2 with a 114 lsa, and a G5X2 with a 112 LSA?
Thanks, Shawn
Also, when a cam spec (LSA) is given as 112 + 4 or 114 + 4, I know that means that 4 degrees of advance is ground into the cam. Practically speaking, what does that do? Does it affect idle, rpm peak, P to V clearance, etc? Or does it just have to do with the valvetrain events (valves opening and closing at a certain point)?
I guess what I'm asking is what would be the practical differences between a G5X2 with a 114 lsa, and a G5X2 with a 112 LSA?
Thanks, Shawn
09-29-2003, 08:07 PM
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Re: Cam LSA and advance questions..... [Large cams] Shawn,
All things being equal in the two cams with the only exception being the LSA the only thing that would change would be the amount of overlap for a given duration. That being said overlap is directly responsible for the "lope" that is audible in an engine. A carbureted application would respond better to a narrower(112) LSA due to the fact that the signal during overlap is required for correct fuel atomization and a fuel injected application would respond to a wider LSA (114) and the increased idle vacuum resulting from less overlap.
As for advancing or retarding the cam, that is measured off the intake centerline of the cam and is not relative to the given LSA which is ground into the cam and cannot be changed.
Advancing the cam opens the intake valve sooner, gives more low end torque,decreases Intake valve to piston clearance, and increases exhaust valve to piston clearance.
Retarding the cam opens the intake later, increases top end power, increases intake valve to piston clearance, and decreases exhaust valve to piston clearance.
This an extreme simplification of a complex subject.
Hope this helps,
Bob
All things being equal in the two cams with the only exception being the LSA the only thing that would change would be the amount of overlap for a given duration. That being said overlap is directly responsible for the "lope" that is audible in an engine. A carbureted application would respond better to a narrower(112) LSA due to the fact that the signal during overlap is required for correct fuel atomization and a fuel injected application would respond to a wider LSA (114) and the increased idle vacuum resulting from less overlap.
As for advancing or retarding the cam, that is measured off the intake centerline of the cam and is not relative to the given LSA which is ground into the cam and cannot be changed.
Advancing the cam opens the intake valve sooner, gives more low end torque,decreases Intake valve to piston clearance, and increases exhaust valve to piston clearance.
Retarding the cam opens the intake later, increases top end power, increases intake valve to piston clearance, and decreases exhaust valve to piston clearance.
This an extreme simplification of a complex subject.
Hope this helps,
Bob
