[DeTomaso] C302B heads & Rocker Arms

[Daniel C Jones]

> Saw some C302B heads.  They had 1.63 ratio rockers in them.

More likely they were 1.65:1 ratio rockers.  The standard ratio is 1.73:1,
with the usual alternate ratios being 1.8:1 or 1.65:1, though there are
other ratios available.  Often the 1.65:1 ratio rockers are used on the
exhaust side of a cam with a dual pattern.  My custom cam was spec'd with
a longer duration lobe on the exhaust but shorter rocker ratio to keep
intake and exhaust lift similar.  For heads with a reasonable intake to
exhaust flow balance, Vizard suggests the rocker ratio on exhaust is best
kept 0.1 to 0.2 of a ratio lower than the intake ratio.  He states that the
exhaust is less sensitive to valve acceleration than the intake but is
sensitive to duration.

> Maybe someone was trying to balance the exceptional intake flow of these
> heads with the not-as-good exhausts for a particular cam.

All the C302B's I've flow tested have had a good intake-to-exhaust flow
ratio.  However, it's not unusal to see heads that were ported for high
compression (15:1) engines intentionally biased towards the intake.
High compression engines require less relative exhaust flow.

Dan Jones