ivc, dcr and actual ivc

[hydrolastic]

Hello guy's, bear with me i hope i can explain the correctly. BMC A series performance regrind cam 284 in 294 ex currently timed at 107 lc
The cam card says ivo at 38 BTDC IVC at 66 Now it's pretty close (within 3 degrees of the cam card Lc of 104) ( i have offset cam keys) when i had the dial indicator on the pushrod side of the rocker but i thought i would check the lift .360 at the valve but now the IVO is 30 degrees BTDC and the IVC is 56 ABDC so it seems the lash has taken about 8 to 10 degrees off the advertised duration.
My question is that i calculated the DCR of the advertised IVC (66) not the actual IVC of 56 degrees. Do i now have to redo my DCR calculations to the actual IVC? Thank you. Aaron

[wyrmrider]

Hard to tell what the advertised clearance is supposed to be
do they give you a valve lash to work with to set the timing
is this a symmetrical or asymmetrical cam?
you can double check by measuring down from the nose an equal amount, splitting the difference and getting an approximate point for lobe centers
do both intake and exhaust and you can calculate your lca
but do not over-think this
what's your cranking compression with a gauge?
is this a regrind?
If so you may want to check that the grinder did not move the new grind around on the old lobes to make the new profile fit
but how are you going to advance or retard if needed?
Just how sensitive is an A series motor anyway? what's your usage?

[David Redszus]

My question is that i calculated the DCR of the advertised IVC (66) not the actual IVC of 56 degrees. Do i now have to redo my DCR calculations to the actual IVC? Thank you. Aaron

Pay no attention to the advertised IVC. Tighter lash will increase duration, looser lash will decrease duration.

Recalculate DCR with the actual valve events at the lash settings that you will actually run.