Lash change effect on seat duration

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blackflag
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Lash change effect on seat duration

Post by blackflag »

How many degrees of seat duration does a lash change of .004 make? Thanks
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CamKing
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Re: Lash change effect on seat duration

Post by CamKing »

Depends on which direction you're changing the lash, and the ramp velocity.
Anywhere from 8 to 40 degrees
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Re: Lash change effect on seat duration

Post by hysteric »

CamKing wrote: Fri May 17, 2019 2:29 pm Depends on which direction you're changing the lash, and the ramp velocity.
Anywhere from 8 to 40 degrees
I take it the 8-40 are the 2 extremes of ramp velocity scale?

Would it be safe to say that the 40 degree change would be a very slow ramp? And if so would that .004 make little difference to actual performance because the valve is barely open?
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Re: Lash change effect on seat duration

Post by Stan Weiss »

Comp Cams SBF Solid Roller. Cam Card calls for .021" also shown at .017" and .025" Note more than just seat-to-seat duration changes.

Stan

PS Let me add since it effects difference in lifter raise this is with 1.65:1 rocker arm ratio.

Code: Select all

Lash_=_.021"_what_cam_card_wants
VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____47.69_|__84.37_|_312.05_|__61.01
_________0.00600____44.55_|__80.80_|_305.35_|__60.99
_________0.01000____42.73_|__78.67_|_301.39_|__60.98
_________0.02000____38.71_|__73.99_|_292.70_|__60.91
_________0.04000____32.32_|__66.84_|_279.16_|__60.69
_________0.05000____29.68_|__63.94_|_273.61_|__60.56
_________0.10000____18.96_|__52.59_|_251.56_|__59.70
_________0.15000____10.52_|__43.84_|_234.35_|__58.68
_________0.20000_____3.06_|__36.19_|_219.26_|__57.27
_________0.25000____-3.97_|__29.07_|_205.10_|__55.41
_________0.30000___-10.85_|__22.20_|_191.36_|__53.71
_________0.35000___-17.79_|__15.20_|_177.41_|__51.04
_________0.40000___-24.96_|___7.98_|_163.03_|__48.74
_________0.45000___-32.52_|___0.38_|_147.86_|__45.30
_________0.50000___-40.80_|__-7.88_|_131.31_|__41.46
_________0.55000___-50.19_|_-17.26_|_112.55_|__36.16
_________0.60000___-61.45_|_-28.50_|__90.05_|__29.76
_________0.65000___-76.72_|_-43.55_|__59.73_|__20.32

-------------------

Lash_=_.017"
VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____50.15_|__87.08_|_317.23_|__61.64
_________0.00600____46.57_|__83.12_|_309.69_|__61.62
_________0.01000____44.55_|__80.80_|_305.35_|__61.61
_________0.02000____40.22_|__75.74_|_295.97_|__61.50
_________0.04000____33.48_|__68.09_|_281.57_|__61.30
_________0.05000____30.71_|__65.07_|_275.78_|__61.15
_________0.10000____19.71_|__53.37_|_253.08_|__60.20
_________0.15000____11.15_|__44.49_|_235.64_|__59.16
_________0.20000_____3.64_|__36.78_|_220.42_|__57.71
_________0.25000____-3.42_|__29.63_|_206.21_|__56.06
_________0.30000___-10.30_|__22.75_|_192.46_|__54.09
_________0.35000___-17.23_|__15.77_|_178.54_|__52.11
_________0.40000___-24.38_|___8.57_|_164.20_|__49.07
_________0.45000___-31.88_|___1.01_|_149.12_|__45.60
_________0.50000___-40.10_|__-7.19_|_132.71_|__41.73
_________0.55000___-49.39_|_-16.45_|_114.16_|__36.93
_________0.60000___-60.46_|_-27.51_|__92.03_|__30.55
_________0.65000___-75.22_|_-42.07_|__62.72_|__21.75

-------------------

Lash_=_.025"VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____45.55_|__81.92_|_307.46_|__60.39
_________0.00600____42.73_|__78.67_|_301.39_|__60.37
_________0.01000____41.04_|__76.70_|_297.74_|__60.35
_________0.02000____37.29_|__72.36_|_289.65_|__60.29
_________0.04000____31.25_|__65.63_|_276.88_|__60.05
_________0.05000____28.68_|__62.87_|_271.55_|__59.95
_________0.10000____18.22_|__51.82_|_250.04_|__59.10
_________0.15000_____9.89_|__43.20_|_233.10_|__57.91
_________0.20000_____2.49_|__35.60_|_218.09_|__56.61
_________0.25000____-4.52_|__28.52_|_204.00_|__55.00
_________0.30000___-11.40_|__21.65_|_190.25_|__53.00
_________0.35000___-18.36_|__14.63_|_176.27_|__50.69
_________0.40000___-25.54_|___7.39_|_161.85_|__48.00
_________0.45000___-33.15_|__-0.25_|_146.60_|__45.01
_________0.50000___-41.51_|__-8.58_|_129.91_|__40.68
_________0.55000___-51.01_|_-18.07_|_110.91_|__35.93
_________0.60000___-62.48_|_-29.52_|__88.00_|__28.98
_________0.65000___-78.29_|_-45.10_|__56.61_|__18.90
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Re: Lash change effect on seat duration

Post by F-BIRD'88 »

No, the 40 deg change would be if you are beyond the lash ramp, getting up on the opening flank /closing flank of the cam.
Not where you want the running lash point to be.
You can play with lash +/- but stay on the lash ramp of the cam lobe...
How do you know where the lash ramp ends?
You can ask the cam grinder/designer.
You can measure it yourself with a CAM DR
Or on the motor with dial indicator and degree wheel.
The "lash point" on a cam lobe may be slightly different on the opening and closing sides.
If you set the lash too loose, now the closing valve seats much harder. More noise, accelerated valve seat wear, valve may bounce at rpm. Not good.
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Re: Lash change effect on seat duration

Post by Stan Weiss »

F-BIRD'88 wrote: Fri May 17, 2019 10:43 pm No, the 40 deg change would be if you are beyond the lash ramp, getting up on the opening flank /closing flank of the cam.
Not where you want the running lash point to be.
You can play with lash +/- but stay on the lash ramp of the cam lobe...
How do you know where the lash ramp ends?
You can ask the cam grinder/designer.
You can measure it yourself with a CAM DR
Or on the motor with dial indicator and degree wheel.
The "lash point" on a cam lobe may be slightly different on the opening and closing sides.
If you set the lash too loose, now the closing valve seats much harder. More noise, accelerated valve seat wear, valve may bounce at rpm. Not good.
You seen to not want to listen to what a cam grinder/designer has just told you. #-o

Lets look at the Chevy 30 30 cam. Should have lash of .030"
@ 0.26" lash seat-to-seat increase about 25 degrees.
@ 0.22" lash seat-to-seat increase about 53.8 degrees.

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Re: Lash change effect on seat duration

Post by cgarb »

Please, we all could use a lesson on how to correctly lash valves again...after all nobody out there is intelligent enough to figure that out on their own.
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Re: Lash change effect on seat duration

Post by F-BIRD'88 »

And what is the seat to seat duration change on that 30-30 cam when you increase the lash from .030" to .035" and then increase the lash to .040" ?
And what is the "lash point" on that cam.
Where the lash ramp becomes the open/close flank.

What is the effective seat to seat running duration change of a hyd cam where you replace the hyd lifters with solids and set a slight lash. Eg: .004" lash or .006" lash?
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Re: Lash change effect on seat duration

Post by Stan Weiss »

So you have a "lash point" which I will call a given "lifter raise".

At that given "lifter raise" how does changes in rocker arm ratio and / or RPM effect seating velocity?

Do you have a max seat velocity that you done want to go over?

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