Basically the early Lucas units, up to the late 60s, had a symetrical cam
lobe & a tendency to bounce the points at medium-high rpm, with the standard
points. There are/were different points available with more spring tension, or
you can add a spring strip, to raise the limit using this unit. The later
assymetrical lobe design has a ramp that opens them quicker & increases the
coil
saturation time, allowing a more reliable spark at high speed. Then they
came out with the 45D unit which was designed for the HEI system. It has the
larger body, cap & rotor, & the cap has walls inside, all designed to prevent
spark-scatter from the HEI.
A point type distributor based on the 45D body, assymetrical cam, good
points with a locked braker plate, is good for over 7000 rpm in a 4 cylinder,
reliably. (example- my girlfriends POS 1275 Sprite will pull reliably to 8k).
For
max reliability or regular use over 7000, I normally will fit an optical
trigger unit such as Allison or Lumenition.
6 cylinder engines are a different story since the saturation time is
obviously decreased by having 6 impulses per distributor rev vs 4. Dual point
systems were really designed for 8 cylinder engines, where there is absolute
minimal saturation time.
It goes without saying that the distributor has to be in good shape re
shaft, bushings, breaker plate, etc & a critical point is the indexing of the
breaker plate to the body. If it's not locked in the correct orientation, the
rotor tip won't line up with the contact in the cap. You can see where the
spark is going by looking at the carbon track on the tip of the rotor.
Safety FasTR,
Glen
|