LCA (lobe center angle) vs LSA (lobe seperation angle)

grumpyvette

Administrator
Staff member
Hey grumpyvette??
I've seen cams listed with one or the other or in some cases both. Where can I find a discussion about the difference and why I care. (As much as I hate to say this I thought they were the same... .

I do know that a smaller separation means a more lumpy idle but how does center-line figure into the mix? Does one trump the other when choosing a cam. It's time to educate.. AGAIN!



First Id point out that nearly everyone occasionally confuses or at least makes the mistake of using the wrong abbreviation, (LSA, and LCA) these are terms,that are almost, at least in many discussions interchangeable. which they are not.
LSA =LOBE SEPARATION ANGLE ........LSA is ground into the cam during manufactured, and can,t change,

LOBE SEPARATION ANGLE
Above 114 Deg. = Extremely Wide
114-112 Deg. = Wide
112-110 Deg. = Moderately Wide
110-108 Deg. = Moderate
108-106 Deg. = Moderately Tight
106-104 Deg. = Tight
Below 104 Deg. = Extremely Tight

VARYING LOBE SEPARATION ANGLE
Tighten.................................................Widen
Moves Torque to Lower RPM.................Raise Torque to Higher RPM
Increases Maximum Torque..................Reduces Maximum Torque
Narrow Power Band..............................Broadens Power Band
Builds Higher Cylinder Pressure............Reduce Maximum Cylinder Pressure
Increase Chance of Engine Knock.........Decrease Chance of Engine Knock.
Increase Cranking Compression...........Decrease Cranking Compression
Increase Effective Compression............Decrease Effective Compression
Idle Vacuum is Reduced........................Idle Vacuum is Increased
Idle Quality Suffers...............................Idle Quality Improves
Open Valve-Overlap Increases.............Open Valve-Overlap Decreases
Closed Valve-Overlap Increases...........Closed Valve-Overlap Decreases
Natural EGR Effect Increases................Natural EGR Effect is Reduced
Decreases Piston-to-Valve Clearance...Increases Piston-to-Valve Clearance
LCA =(LOBE CENTER ANGLES)remember lobe center angles can be changed thru indexing the cam when degreeing it in
ADVANCING / RETARDING CAM TIMING

KEEP IN MIND MANY CAMS ARE FACTORY SET UP TO BE 4 DEGREES ADVANCED if INSTALLED DOT-TO-DOT

ADVANCING.
Begins Intake Event Sooner........................
Open Intake Valve Sooner..........................
Builds More Low-End Torque.......................
Decrease Piston-Intake Valve Clearance....
Increase Piston-Exhaust Valve Clearance...

RETARDING
Delays Intake Event Closes Intake
Keeps Intake Valve Open Later
Builds More High-End Power
Increase Piston-Intake Valve Clearance
Decrease Piston-Exhaust Valve Clearance

http://garage.grumpysperformance.co...ng-cam-and-shifting-the-lca.10553/#post-44949

http://garage.grumpysperformance.co...et-it-to-last-cam-install-info.90/#post-57942
camtimebush.png

lobe_diagram_lg.jpg







LSA_01.jpg
0810chp_05_z+comp_cams_camshaft_technology_insite_tech+lobe_separation_angle.jpg


116_0403_basic_10_z.jpg


READ THRU THESE CAREFULLY
http://www.compcams.com/Community/Artic ... 2026144213

http://www.popularhotrodding.com/tech/0 ... index.html

http://www.hotrod.com/techarticles/113_ ... index.html

http://www.circletrack.com/techarticles ... ation.html

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=480

viewtopic.php?f=52&t=2782&p=7215&hilit=+overlap#p7215

viewtopic.php?f=52&t=90

viewtopic.php?f=52&t=2782&p=7433&hilit=+overlap#p7433


example
LOOK heres TWO cams IDENTICAL EXCEPT FOR THE LSA,(LOBE SEPARATION ANGLES) assuming both cams are installed with identical LCA (LOBE CENTER LINE ANGLE)remember lobe center angles can be changed thru indexing the cam when degreeing it in, LSA is ground into the cam during manufacture, the tighter LSA of the crane 110921 builds a bit more cylinder pressure and results in slightly more torque over a NARROWER rpm band so its better with a manual transmission, the crane 114681 with its wider LSA tends to work better with an auto trans with its wider torque band but very slightly lower peak torque, the crane 110921 has more overlap and better savaging in the mid rpm band, but it idles rougher at low rpms and that overlap doesn,t help if you use nitrous
COMPARE the TIMING

110921.jpg

narrower LSA, more overlap & more effective compression, because the intake valve closes earlier
114681.jpg

wider LSA, less overlap & less effective compression, because the intake valve closes later



USING THE .050 LIFT figures, notice that the tighter LSA (LOBE SEPARATION ANGLE)cam CRANES 110921 has the intake close at 45 degrees ABDC while the wider lsa CRANES 114681closes the valves at 50.0 ABDC (the wider LSA results in the valve closing 5 degrees later on the pistons compression stroke, effectively reducing the effective compression ratio
 
Last edited by a moderator:
heres a reasonably useful chart for selecting a compatible LSA
READ THRU THIS LINK

http://www.popularhotrodding.com/tech/0 ... index.html

lcadc1.jpg

"Lobe Centerline Angle Determination Chart
To use this chart, first establish the number of cubes in the INDIVIDUAL cylinder, per inch of valve diameter. To get this number, divide the engine displacement by the number of cylinders, then by the intake valve diameter. Find that number on the vertical axis, then move across to the green line. At the intersection point, drop down to the base and read off the LCA required. Because big-block Chevys have angled valves, they need to have about 2 degrees less than this chart indicates.
"


examples

1

lets assume your building a 383 SB chevy
383/8=47.875 round that off to 48 cubic inches per cylinder
divide that by the intake valve diam, of 2.02 and we get 23.76
using the chart and plugging in the numbers we find that about a 106 LSA is about ideal

2

lets assume your building a 540 BB chevy

540/8=67.5 round that off to 68 cubic inches per cylinder
divide that by the intake valve diam, of 2.30 and we get 29.56
using the chart and plugging in the numbers we find that about a 101 LSA is about ideal


3

lets assume your building a 283 SB chevy
283/8=35.375 round that off to 35 cubic inches per cylinder
divide that by the intake valve diam, of 2.02 and we get 17.5
using the chart and plugging in the numbers we find that about a 113 LSA is about ideal
 
Last edited by a moderator:
I know this is an old thread but I just found it. If I understand you correctly LSA and LCA are related yet separate. At the end is David Vizard's graph for determining LCA based on the ratio of CI of one cylinder to the diameter of the intake valve. My question is in all three examples when using the chart the reading is given as the required LSA but I thought the chart refered to the required LCA which is not exactly the same thing. Is the chart actually refering to LSA or LCA?

Jason
 
thats a good question and I'm sure it needs to be discussed here in more detail.
the chart below,is supposed to point out LSA, but its
mislabeled



before you reach for your wallet, do some basic math and read a few dozen related links
http://www.wallaceracing.com/calcafhp.php

http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/

http://www.gmhpclub.com/performancecalculators.htm

http://garage.grumpysperformance.com/index.php?threads/port-speeds-and-area.333/#post-37705
USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations
http://www.wallaceracing.com/runnertorquecalc.php
http://www.wallaceracing.com/ca-calc.php
http://www.wallaceracing.com/area-under-curve.php
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.circletrack.com/enginetech/1 ... ch_engine/



http://www.wallaceracing.com/calcafhp.php

http://hpwizard.com/engine-horsepower-calculator.html

http://www.hotrod.com/articles/airflow-research-cylinder-power/

http://www.powerperformancenews.com/tech-articles/cylinder-head-tech-airflow-vs-power/

http://www.calculator.net/engine-horsepower-calculator.html

http://www.calculatoredge.com/new/horsepower.htm

lcadc1.jpg

0810chp_05_z+comp_cams_camshaft_technology_insite_tech+lobe_separation_angle.jpg


116_0403_basic_10_z.jpg


(LOBE SEPARATION ANGLE)
which can,t be changed once the cam is manufactured
LCA
(lobe CENTER ANGLE)
Which can be adjusted by advancing or retarding the cams index to the crank rotation, as desired
with bushings or an adjustable timing set.
keep in mind the goal here is to increase or decrease the overlap , that occures as that has a major effect on the efficiency of the headers ability to efficiently scavenge the cylinders while both valves are simultaneously open

exhaustpressure.jpg

EXFLOWZ4.jpg
 
Last edited:
Thanks for the clarification. Do you find that his chart is accurate as to a general rule? Does this chart apply to inline motors as it is generally applied to V8's. I'm asking as I have a Ford 300 inline six, which is essentially a stroked 240. All the parts are interchangeable and share the same block. At 50CI per cylinder and 1.94 valves would require a 102.5 LSA and with 2.02 valves, which is rather large for the cylinder head, would require a 103.5 LSA. That seems awful narrow, but I think I remember seeing where strokers like or prefer narrower LSA's compared to non stroked motors. It would seem from the chart that engines with large cylinders and small valves like a narrower LSA and small cylinders with large valves like a wider LSA. Have you found that to be fairly accurate? Do you think same principles apply to inline as much as it does to V8's, such as valve timing events? Does the fact that the inline 6 has a u shaped flow head versus a crossflow affect cam selection and valve timing events, especially exhaust gas scavenging. Thanks for the time and knowledge put into your answers.

Jason
 
Yes the chart on LSA, is valid and a useful guide, and as the cylinder displacement goes up
the tighter LSA becomes more critical to effective breathing efficiency

lcadc1.jpg

tends to be rather accurate and helpful, but the cylinder head port shape and flow restrictions and filling characteristics are far more dependent on the valve curtain area,and how effectively you select components to take full potential advantage of exhaust scavenging during the valve timing overlap period
116_0403_basic_10_z.jpg

porting+valve_area.jpg

and the bore diameter and stroke length and rpm range you intend to allow the engine to breath effectively in than the inline vs v block lay out
duration is the amount of time a valve is off its seat,but keep in mind that the first few degrees at the beginning and end of the valve travel,

LiftCurveAread.gif

are not very conductive to effective air flow rates and the exhaust scavenging, and will be dependent on both the cams duration and intended rpm range , and the displacement, compression ratio and how efficient the exhaust scavenging is,
EXFLOWZ4.jpg

and that always requires a low restriction exhaust and headers designed to match the other components, if your going to expect anything even approaching , efficient cylinder fill rates

volumetric.gif

related info
http://garage.grumpysperformance.com/index.php?threads/is-backpressure-hurting-your-combo.495/

http://garage.grumpysperformance.com/index.php?threads/x-or-h-pipe.1503/

http://garage.grumpysperformance.com/index.php?threads/calculating-required-exhaust-pipe-size.11552/

http://garage.grumpysperformance.com/index.php?threads/calculating-header-design.185/
 
Last edited:
Back
Top