[Mgs] Pertronix and overheating in MGA

[Paul Hunt]

Does the Pertronix say it *should* be 60 degrees?  Or are you just going by
what the points are?  Points give a fixed dwell in degrees or percent over the
range of engine revs as it is governed by the shape of the cam.  This means
that as the revs rise the points closed i.e. dwell i.e. coil recharge *time*
gets shorter and shorter.  At high revs (and by that I mean higher than our
engines usually go) you can get insufficient coil charge time and a reducing
spark.  By contrast electronic systems generally give a fixed dwell *time*
which means the degrees or percent may well be low to start with but should
increase as the revs rise.  At higher rpms an electronic trigger should be
giving a longer coil recharge time than points.  The difference is negligible
at the sort of rpms the MGA and MGB engines run at, V8 engines only have half
the dwell and coil recharge time that the 4-cylinder engines do and very
nearly the same peak rpm and don't suffer from weak spark.  This is why
dual-point systems are a waste of money but twice the trouble on 4-cylinder
MGA and MGB engines.

PaulH.

  ----- Original Message -----
  ... The Pertronix dwell was
  only 40 degrees, versus the desired 60.