LS376/480 query

[teamHOLDENracing]

Gents

I'm having some custom manifolds made for my LS376/480 and have all the technical specs required for calculating optimal primary lengths except one: timing (in degrees) that the exhaust valve starts to open before the piston reaches TDC.

I can't find the info anywhere and getting anything out of GM is proving impossible.

Can anyone point me in the right direction?

Many thanks

Andy

[harry b]

You could just measure it out with a degreekit.

[teamHOLDENracing]

Any way of doing that without taking a head off?

[Boosted LS1]

If you know the exhaust centreline and duration (divide by 2)then you should be able to count backwards to the valve opening point.