MSD v CDI

[SteveF_911]

I have a 66 2.0 with Webers and a points ignition system.

I am about to upgrade my ignition to either a MSD or a M&W CDI unit. The M&W being a copy of the Bosch CDI as used in most 911.

I use the car mostly for historic and club racing and have found I have a plug fouling problem when the car has been idling for a while. This always clear after a short time but it can be a bit of a problem when I compete in historic rallies and have to wait for my turn at the cucuit.

Question. What are the advantages/disadvantages of the MSD over a more conventional CDI?

Price is about the same.

Thanks in advance
Steve

[Early_S_Man]

Steve,

I think the M&W folks would be quite furious at the implication that their unit is merely a 'copy' of the Bosch CDI! A functional replacement of similar size, yes ... but the design appears to be quite a bit more recent [perhaps as much as 15 years] than the msd. In the operational rpm range of an early 911 engine ... the MSD box isn't putting out multiple sparks, anyway, so any claims in that area are really a moot point! Above 3000 rpms the MSD is a completely traditional CDI ignition, pure and simple!

For your purposes, I suspect very little difference in performance. Being that M&W is a 'local' company for you , and also since no other Pelicahead has tried the M&W unit ... I say 'buy local' and let us know how it performs!

Another low-cost alternative would be to find a used Bosch CDI unit and install it ... eBay has them at quite reasonable prices from time to time. That would be my personal choice, BTW!

[SteveF_911]

Warren,

Thanks for the advice, I have been in contact with the M&W people and I think I will give there unit a go. They are not realy an expensive option and the Bosch units are hard to find over here. The ones that are available are going for a premium.

Quote from M&W

"We are currently designing a true Porsche replacement unit which will not
only look like the original unit but also have a true selectable rev
limiter.

Regards

Wayne
M&W"

[sithot]

Having discussed this very matter with Neil Harvey (here in the States) at Performance Developments, I'm quite satisfied that the M&W is a better mousetrap. Whether I'll get one or not is another story. It is however, a very slick piece of equipment and he promised me it would definitely fire my plugs!

http://www.performancedevelopments.com/

Tom

[Lorenfb]

"The M&W being a copy of the Bosch CDI as used in most 911."

A copy? Really now!

Why would anyone consider using a CDI unit which is more complex and thus
potentially less reliable than the VERY simple and PROVEN (30+ years) Bosch
unit? Many Porsche owners are aware of the aftermarket CDI units and their
poor reliablility records.

An ignition unit should do the following & anyone more is marketing hype:

1. produce a minimum energy level - 60 millijoules
2. produce adequate output voltage to the spark plugs - 30KV to 40KV
3. simple in design
4. can withstand temp variations - -20 deg F to 150 deg F
5. can withstand voltage variations - 6 volts (cranking) to 16 volts (overvoltage)
6. not require special wiring, e.g. tach adapters, or mounting brackets
7. not require special ignition coils

Check out this web site ( www.systemsc.com ) on the Technical page on the
Ignition Systems section for some insights on ignition systems.

Given the lack of real benefits of aftermarket CDIs, why risk a potential CDI
failure with a unit other than a Bosch unit? I guess one can always buy two
and keep a backup in the trunk.

Pelican Parts has many sources for rebuilt parts, e.g. Bosch CDI units.