MSD - Even / Odd Cylinders

[JK McDonald]

I am being told that each MSD Ignition box should be selected to match the part number and the application. Some units have rev-limiters, hotter spark, and special additional applications or uses.

This seems straightforward enough. But then I am given some technical jargon stating that PN 6200 is for 4 –6 – 8 cylinder cars with even firing cylinders. PN 6246 is for 4-6-8 cylinder cars with odd firing cylinders. I am told that this has something to do with the rev-limiting function. Please help.

Thanks, Karen

The explanation below concerning the rotational odd / even cylinder firing cycle makes a lot of sense. Thank you for your help -

Karen

[jluetjen]

The 911 motor is an even firing 6-cylinder, which means that a cylinder fires every (2x360)/6 degrees or 120 degree. There are some GM, Ford(?) and Maserati V6's which are odd firing V6's as a result of their cylinder banks being 90 degrees apart (or at least not at a 60 degree angle) and they maintained a common crank pin. The result is that the cylinders fire with a pattern of 90-30-etc between individual ignition events. V4's like Lancia's, and boxer 4s have a similar feature.

To be honest. most of these engines were designed as V8's less 2 cylinders to so that they could share manufacturing tooling with the V8's. They're OK for lower rev applications, but tend to be rough at higher rev's.

But fear not, Porsche never compromised their 6 cylinder and 8 cylinder designs in this fashion.