Actual seat timing of tight lash [.016] vs @.020 UDHarold voodoo solid flat

[Pappy]

If my Voodoo solid flat calls for lash set at .016, how much does actual seat timing differ from the duration @.020?

[Geoff2]

That would depend on rocker ratio.
0.016" lash at the valve with 1.5 rockers means 0.011" tappet lash, [ tappet off the seat 0.011" ]. 1.7 rockers & the tappet lash becomes 0.0095".

[blackford]

If my Voodoo solid flat calls for lash set at .016, how much does actual seat timing differ from the duration @.020?

.020 lash vs .016 lash will change your seat-to-seat duration by several degrees. If your cams ramps are mild SFT street ramps, it could be quite a bit more because the opening/closing ramps are very gradual. I'll give you an example from EA Pro. If I change the actual lash from .016 to .020 on a street SFT cam, the seat-to-seat timing decreases by about 14 degrees. This is due to the slow opening and closing ramps, so even though it's only a few thousandths of valve lift, it's a lot in terms of seat-to-seat duration.

I have a Comp Cams street Magnum SFT cam that I lash to .015 instead of the recommended .022. The seat-to-seat duration changes from approximately 287 to 308. Changing from 1.7 to 1.5 rockers changes seat-to-seat duration from approximately 285 to 306. I say "approximately" because EA Pro gives duration at .003 valve lift and not seat-to-seat, plus EA Pro makes some assumptions on the opening/closing ramps of my cam. The ramp rating of my cam is in the low 30s based on 236 duration @ .050 tappet lift and 145 duration @ .200 tappet lift. If your cam has more aggressive ramps, then the change in seat-to-seat duration will probably be less.

[Stan Weiss]

If my Voodoo solid flat calls for lash set at .016, how much does actual seat timing differ from the duration @.020?

That would depend on rocker ratio.
0.016" lash at the valve with 1.5 rockers means 0.011" tappet lash, [ tappet off the seat 0.011" ]. 1.7 rockers & the tappet lash becomes 0.0095".

Geoff,
While is answering your question if he also posts up the 0.020" duration and 0.050" duration he could then get a rough estimate for his seat duration.

Stan

[Pappy]

The cam is 266/276 @.020 and 233/241 @ .050
It is a tight lash cam and calls for .016” lash with a 1.5 rocker.
I’m almost certain from Harold’s posts that he didn’t use constant velocity ramps, and my guess is that his ramps were more of a constant acceleration type. What I’d like is to know is when my intake is actually closing. I’m thinking his closing side is about 3 degrees later due to asymmetry and then I’m expecting the duration at the seat is a bit more than @.020. Just trying to understand what I have and if 9.6 CR is enough with an aluminum head, or if I can go higher and still be safe.
This is for a 331sbc.

Eric

[Horder]

I recall a time when Harold was discussing the advertised durations of the VooDoo solid flat tappets. He made mention that the advertising group had more say in those #’s than they should have. He was happy with the advertised durations in the catalog for the hydraulics but the solids came out after and the numbers were “massaged”. I believe that cam to be a bigger cam than the #’s indicate. A friend ran one in a 10.25:1 327 with 461 heads. No issue on pump fuel at all. Great cam. Tremendous throttle response.

I know you are looking for specifics. I apologize that my answer is vague.

[Tom68]

The cam is 266/276 @.020 and 233/241 @ .050
It is a tight lash cam and calls for .016” lash with a 1.5 rocker.
I’m almost certain from Harold’s posts that he didn’t use constant velocity ramps, and my guess is that his ramps were more of a constant acceleration type. What I’d like is to know is when my intake is actually closing. I’m thinking his closing side is about 3 degrees later due to asymmetry and then I’m expecting the duration at the seat is a bit more than @.020. Just trying to understand what I have and if 9.6 CR is enough with an aluminum head, or if I can go higher and still be safe.
This is for a 331sbc.

Eric

Aly heads, 9.6:1 bit of a cam, vehicle weight and gearing ? Nonetheless you should get away with 87, go up in comp if you want to run better fuel.

[Stan Weiss]

The cam is 266/276 @.020 and 233/241 @ .050
It is a tight lash cam and calls for .016” lash with a 1.5 rocker.
I’m almost certain from Harold’s posts that he didn’t use constant velocity ramps, and my guess is that his ramps were more of a constant acceleration type. What I’d like is to know is when my intake is actually closing. I’m thinking his closing side is about 3 degrees later due to asymmetry and then I’m expecting the duration at the seat is a bit more than @.020. Just trying to understand what I have and if 9.6 CR is enough with an aluminum head, or if I can go higher and still be safe.
This is for a 331sbc.

Eric

Sorry I don't have any Cam Doctor files for Lunati cams. I have some rough numbers from a Lunati VooDoo 704 HFT lobe that I have adjusted some.

Stan

_______I__N__T__A__K__E
Rocker_Arm_Ratio_=_1.500_________Valve_Lash_=_0.01600________Valve_Angle_=_23.0

VALVE_____Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area
_________0.00000____28.00_|__73.00_|_281.00_|__39.53
_________0.00600____24.72_|__68.13_|_272.85_|__39.52
_________0.01000____22.87_|__65.60_|_268.48_|__39.50
_________0.02000____18.98_|__60.58_|_259.56_|__39.43
_________0.04000____12.84_|__53.34_|_246.18_|__39.24
_________0.05000____10.24_|__50.47_|_240.72_|__39.13
_________0.10000____-0.42_|__39.51_|_219.09_|__38.32
_________0.15000____-9.71_|__30.30_|_200.59_|__37.20
_________0.20000___-19.07_|__20.99_|_181.92_|__35.44
_________0.25000___-28.68_|__11.36_|_162.68_|__33.41
_________0.30000___-38.62_|___1.37_|_142.75_|__30.66
_________0.35000___-49.11_|__-9.13_|_121.75_|__27.08
_________0.40000___-60.83_|_-20.85_|__98.32_|__22.94
_________0.45000___-75.75_|_-35.74_|__68.51_|__16.56
CAM_____________________________________________________ICL
_________0.00600____33.91_|__83.59_|_297.50_|__27.92_|_114.84
_________0.01000____28.66_|__74.02_|_282.67_|__27.87_|_112.68
_________0.02000____21.22_|__63.42_|_264.64_|__27.74_|_111.10
_________0.04000____11.77_|__52.15_|_243.92_|__27.43_|_110.19
_________0.05000_____8.08_|__48.16_|_236.24_|__27.28_|_110.04
_________0.10000____-6.76_|__33.22_|_206.46_|__26.18_|_109.99
_________0.15000___-20.78_|__19.28_|_178.50_|__24.45_|_110.03
_________0.20000___-35.40_|___4.61_|_149.21_|__21.82_|_110.00
_________0.25000___-51.10_|_-11.12_|_117.78_|__18.20_|_109.99
_________0.30000___-70.35_|_-30.35_|__79.31_|__12.94_|_110.00

[CamKing]

If my Voodoo solid flat calls for lash set at .016, how much does actual seat timing differ from the duration @.020?

Stan's numbers are pretty close. It'll gain about 18 degrees. 7 on the opening side, and 11 on the closing side.
Harold's lobes are symmetrical from about .050" and up. What makes them asymmetrical, is the lack of a lash ramp on the opening side.
On the closing side, he slows the valve down as it reaches the lash point. On the opening side, he accelerates the lift curve, right off the base circle.

[Pappy]

Thank you all.

Eric