View Single Post
CamB CamB is offline
CamB's Avatar
Join Date: Apr 2000
Location: Auckland, New Zealand
Posts: 5,111
I fall into the camp which thinks that:

- an MSD is cheaper than a second hand Bosch
- it is new, not second hand
- the multiple sparks below 3000rpm seem to help plug fouling and low speed driveability on cars which run rich at low RPM (this means carbs and MFI)

The Pertronix, if it sparks twice at >3000rpm, doesn't intuitively add much.

As I understand it, it won't, and can't, replace twin plugging, because twin plugging is needed for:

- very high dome and high compression (it ignites the mixture better, apparently)
- wide pistons with high dome (like 98mm and wider)

The twin plugs fire at the same time - one spark, one explosion - lit at both ends.

There is a good explanation on Steve Weiner's site at

Specifically, about half way down this page:
1975 911S (in bits)
1969 911T (goes, but need fettling)
1973 BMW 2002tii (in bits, now with turbo)
Old 01-28-2004, 08:41 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #19 (permalink)