Camshaft lsa and low end torque

[gregsdart]

As a neophyte in cam specs and design, it has occured to me that a better method of overlap value determination might be a good idea. Case in ooint. I have run two roller cams that look very similar by the .050 numbers, yet probably are much different. Cam A, 283/296/113 @.050, .486 untake lobe lift intake, .460 lobe lift exhaust. Spec'd for a 1.5 rocker, .026 lash.
Cam B, 284/296/113, lobe lift .510 intake,.500 exhaust, spec'd for 1.7 rockers, lash is .019 int, .020 exh, and it is an inverted flank grind roller. I am sure that the overlap potential flow is much higher on cam B, than cam A

[gregsdart]

As a neophyte in cam specs and design, it has occured to me that a better method of overlap value determination might be a good idea. Case in point. I have run two roller cams that look very similar by the .050 numbers, yet probably are much different. Cam A, 283/296/113 @.050, .486 intake lobe lift , .460 lobe lift exhaust. Spec'd for a 1.5 rocker, .026 lash.
Cam B, 284/296/113, lobe lift .510 intake,.500 exhaust, spec'd for 1.7 rockers, lash is .019 int, .020 exh, and it is an inverted flank grind roller. I am sure that the overlap potential flow is much higher on cam B, than cam A

[skinny z]

...a better method of overlap value determination might be a good idea.

Are you referring to the method that determines what the value is? Or a method for determining what the value might be for a given application?

[Stan Weiss]

If you have Cam Dr lobe lift files you can look at area and break the area down to different parts of the lobe like Dr Blair talks about.

The example below is the Crane version of a Pontiac RA IV cam. Note that cam lobe area doesn't change, but the different area break downs will change by advancing or retarding the cam. The break down area will also change with a change in LSA.

Stan

_______I__N__T__A__K__E
Rocker_Arm_Ratio_=_1.500_________Valve_Lash_=_0.00000

Intake_BTDC_(IVO_to_TDC)_=_1.164
Intake_Pumping_(TDC_to_BDC)_=_68.423
Intake_Ramming_(BDC_to_IVC)_=_11.496
Intake_Overlap_(IVO_to_EVC)_=_26.038

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____54.80_|_125.20_|_360.00_|__39.12
_________0.00600____31.84_|__98.92_|_310.76_|__39.05
_________0.01000____26.66_|__87.45_|_294.11_|__38.99
_________0.02000____19.48_|__71.92_|_271.39_|__38.82
_________0.04000____11.12_|__60.95_|_252.07_|__38.51
_________0.05000_____8.00_|__57.35_|_245.35_|__38.37
_________0.10000____-4.12_|__44.21_|_220.09_|__37.37
_________0.15000___-14.18_|__33.72_|_199.54_|__36.08
_________0.20000___-23.73_|__23.98_|_180.25_|__34.28
_________0.25000___-33.32_|__14.25_|_160.93_|__31.96
_________0.30000___-43.49_|___4.01_|_140.51_|__29.14
_________0.35000___-54.83_|__-7.42_|_117.74_|__25.50
_________0.40000___-68.65_|_-21.28_|__90.07_|__20.19
_________0.45000___-89.31_|_-41.84_|__48.86_|__11.16
CAM_____________________________________________________ICL
_________0.00600____27.77_|__90.14_|_297.90_|__26.00_|_121.19
_________0.01000____22.53_|__77.20_|_279.73_|__25.93_|_117.34
_________0.02000____14.78_|__65.40_|_260.18_|__25.78_|_115.31
_________0.04000_____5.21_|__54.28_|_239.49_|__25.46_|_114.53
_________0.05000_____1.45_|__50.18_|_231.64_|__25.27_|_114.37
_________0.10000___-14.18_|__33.72_|_199.54_|__24.05_|_113.95
_________0.15000___-28.41_|__19.15_|_170.75_|__22.12_|_113.78
_________0.20000___-43.49_|___4.01_|_140.51_|__19.43_|_113.75
_________0.25000___-61.28_|_-13.92_|_104.80_|__15.29_|_113.68
_________0.30000___-89.31_|_-41.84_|__48.86_|___7.44_|_113.74

_________0.00600____29.03_|_326.94
_________0.01000____34.27_|_314.00
_________0.02000____42.02_|_302.20
_________0.04000____51.59_|_291.08
_________0.05000____55.35_|_286.98
_________0.10000____70.98_|_270.52
_________0.15000____85.21_|_255.95
_________0.20000___100.29_|_240.81
_________0.25000___118.08_|_222.88
_________0.30000___146.11_|_194.96


_______E__X__H__A__U__S__T
Rocker_Arm_Ratio_=_1.500_________Valve_Lash_=_0.00000

Exhaust_Blow-Down_(EVO_to_BDC)_=_9.685
Exhaust_Pumping_(BDC_to_TDC)_=_54.940
Exhaust_ATDC_(TDC_to_EVC)_=_1.568
Exhaust_Overlap_(IVO_to_EVC)_=_11.289

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BBDC__Deg_ATDC_____________Area
_________0.00000___106.90_|__87.10_|_374.00_|__40.27
_________0.00600____83.70_|__54.16_|_317.86_|__40.21
_________0.01000____78.72_|__43.04_|_301.76_|__40.13
_________0.02000____71.42_|__28.84_|_280.26_|__39.97
_________0.04000____62.85_|__17.97_|_260.82_|__39.66
_________0.05000____59.66_|__14.29_|_253.95_|__39.51
_________0.10000____47.03_|___0.59_|_227.62_|__38.50
_________0.15000____36.48_|_-10.44_|_206.04_|__37.10
_________0.20000____26.59_|_-20.69_|_185.90_|__35.30
_________0.25000____16.71_|_-30.91_|_165.81_|__32.74
_________0.30000_____6.10_|_-41.38_|_144.72_|__29.91
_________0.35000____-5.68_|_-53.53_|_120.79_|__25.93
_________0.40000___-19.98_|_-67.92_|__92.10_|__20.61
_________0.45000___-41.55_|_-89.34_|__49.10_|__11.14
CAM_____________________________________________________ECL
_________0.00600____79.78_|__45.49_|_305.27_|__26.78_|_107.14
_________0.01000____74.54_|__34.02_|_288.56_|__26.70_|_110.26
_________0.02000____66.62_|__22.50_|_269.12_|__26.54_|_112.06
_________0.04000____56.78_|__11.08_|_247.86_|__26.18_|_112.85
_________0.05000____52.86_|___6.84_|_239.69_|__25.98_|_113.01
_________0.10000____36.48_|_-10.44_|_206.04_|__24.73_|_113.46
_________0.15000____21.64_|_-25.75_|_175.89_|__22.80_|_113.70
_________0.20000_____6.10_|_-41.38_|_144.72_|__19.94_|_113.74
_________0.25000___-12.37_|_-60.28_|_107.34_|__15.82_|_113.95
_________0.30000___-41.55_|_-89.34_|__49.10_|___7.43_|_113.90

[JC565Ford]

I don't think that's what MT's point was.I'll take a crack at it MT. Those two camshafts would be massively different but with the same LSA. So comparing them using the LSA would be pointless. Again I'm an ignoramus but it sounds like you (MT) are agreeing with the premise that LSA is largely irrelevant?

Not irrelevant as LSA is related to the actual timing events. LSA is just kind of "short-hand" is describing it.
But you can move the events sooner or later and keep the same LSA. That is possible.

I've only played with it a little in EngMod 4T, but moving around the opening and closing events (narrowing and spreading the LSA) can show some big spreads in the results of an engine. That very much depends on the capabilities of the heads and exhaust used. Everything effects everything.

[Tom68]

...a better method of overlap value determination might be a good idea.

Are you referring to the method that determines what the value is? Or a method for determining what the value might be for a given application?

20 thou overlap numbers would help compare idle quality for cams with different lobe aggressiveness.

[skinny z]

...a better method of overlap value determination might be a good idea.

Are you referring to the method that determines what the value is? Or a method for determining what the value might be for a given application?

20 thou overlap numbers would help compare idle quality for cams with different lobe aggressiveness.

I understand it to be seat to seat timing that bests defines overlap but between hydraulics and solids, I also understand that it's difficult to compare.
That said, cam specs, seat timing and how they're measured are all over the map when you're crossing brands.

[Stan Weiss]

On a solid lifter cam as you change valve lash (doing lash loops) you change seat-to-seat duration and overlap.

Stan

[gregsdart]

I see a lot of difference in the two cam/rocker combos in my post earlier. The higher lift cam has .009 less lash on intake, a higher rocker ratio, a more agressive lobe profile, which all increase potential flow. Stan wiess chart above if i read it right gets into that kind of detail.

[Tom68]

I see a lot of difference in the two cam/rocker combos in my post earlier. The higher lift cam has .009 less lash on intake, a higher rocker ratio, a more agressive lobe profile, which all increase potential flow. Stan wiess chart above if i read it right gets into that kind of detail.

You need it like this to see it BUT you need the curves built from the actual valve movements, rocker ratios aren't constant and you have different ones anyways.

lift-5-650x378.jpg

[Stan Weiss]

As a neophyte in cam specs and design, it has occured to me that a better method of overlap value determination might be a good idea. Case in ooint. I have run two roller cams that look very similar by the .050 numbers, yet probably are much different. Cam A, 283/296/113 @.050, .486 untake lobe lift intake, .460 lobe lift exhaust. Spec'd for a 1.5 rocker, .026 lash.
Cam B, 284/296/113, lobe lift .510 intake,.500 exhaust, spec'd for 1.7 rockers, lash is .019 int, .020 exh, and it is an inverted flank grind roller. I am sure that the overlap potential flow is much higher on cam B, than cam A

Let just do a little rough math.

Cam A ► 0.020 - (.026 / 1.5) = 0.00266667"

Cam B ► 0.020 - (.019 / 1.7) = 0.00882353"

We can do the same thing for 0.050 duration

Cam A ► 0.050 - (.026 / 1.5) = 0.032667" - 283 degrees

Cam B ► 0.050 - (.019 / 1.7) = 0.038824" - 284 degrees

Stan

[JC565Ford]

Overlap is a necessary evil.......

I stopped looking at it that way -

Initiates the beginning of your intake stoke. It's a tool. Figuring out how to use it effectively is the issue, at least for me anyway.

[Tom68]

Overlap is a necessary evil.......

I stopped looking at it that way -

Initiates the beginning of your intake stoke. It's a tool. Figuring out how to use it effectively is the issue, at least for me anyway.

Necessary evil in production cars, a power producing necessity in race cars.

[hoffman900]

Overlap is a necessary evil.......

I stopped looking at it that way -

Initiates the beginning of your intake stoke. It's a tool. Figuring out how to use it effectively is the issue, at least for me anyway.

Necessary evil in production cars, a power producing necessity in race cars.

I think Warp knows some things.

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

You need just enough to “talk” to the intake port. Anymore just sucks fuel out the exhaust. Fuel in the exhaust pipe just makes things glow, it makes no power as it’s now not in the cylinder. George Bryce even talks about how little overlap he runs on his Pro Stock Bike engines.

[Tom68]

Literally, Billy Godbold, Mike Jones, the late Harold Brookshire, and I’m sure unnamed cam designers, all tell you they could care less what the overlap is. It is a result.

Necessary evil, flow though is only bad for economy and emissions, good for chamber purging and flame shows.