Spark Plugs

[chris68]

Can anyone recommend best plugs for a 2.0ltr 'S' spec motor. Is there much to choose between Champion, Bosch, NGK...?

Cheers,
Chris

[frog67elf]

Best plugs for a 2.0S motor are NGK B7ES.
They are fairly cheap at around US$2.50 and are a great alternative to the very expensive Bosch platinum plugs which go for round $US25.0 per plug. I had plug fouling problems for almost 6 months before I figured out the problem. I assume you also have a Bosch or MSD CD bosx right? If not you NEED one. Otherwise, despite the sparkplug upgrade, you will continue to have plug fouling problems. I went to the MSD 6AL CD ox last winter and it makes a world of difference.

[chris68]

Hi,

Thanks for the reply. My car's currently got a standard ballast resistor ignition i.e. ballast resistor, coil and contact breaker - no transistorised ignition unit. It's close to completion after a long restoration so I don't know what the common problems are?

What does the MSD ignition unit do? Is it easy to add?

Many thanks,
Chris

[Barry]

Hi Chris, the MSD unit differs from your current setup as follows.

Your conventional coil runs at 9-10 volts just from your resisted battery voltage. When you turn the starter, the battery voltage is dropped because of the starter motor load, but the ballast resisitor is by-passed to compensate, maintaining a decent spark when cranking. The points directly trigger the coil, and take the full charging current. The condensor is there to eliminate arking at the points. The trouble is that the coil is near its limit running a 6 cylinder engine at 7000 revs, leading to weaker sparking. This in turn leads to a slowdown in the flame front, which means that combustion is not fully completed in time to get the full power from the air/fuel mixture.

An MSD type system uses a dedicated power supply, which is of heavier gauge than the original coil supply. This is direct wired to the battery (via the starter motor terminal in my case). The unit just uses the original coil (or CDI box) feed for an ignition-switched source, to turn the unit on and off. The unit is still triggered by the points: but as these are now acting only as a signal source, they take almost no current, and the condensor is not needed. The unit now takes it's charging current from the new (direct to battery) feed, and charges an internal capacitor. This, when triggered by the points, discharges into the 'coil' (slightly different to the original coil, although it looks the same), at some 400-500 volts. This enables the 'coil' to charge at an much, much quicker rate than standard. It also allows the 'coil' to produce a much greater voltage and current, leading to a larger, hotter spark. In fact there is so much 'sparking energy' available, the unit is able to produce a steady stream of sparks over a crank angle of 15 (ish?) degrees at lower revs (3200 rpm rings a bell). After that the unit produces one very powerful spark.

Benefits I had were very easy starts, smooth idle, bit more power, cleaner running. Did not seem to be any downsides, although be careful working near the HT side with the car running, as the voltages/current are now very, very high!

When you fit an MSD type unit, they have a different type of coil (technically a transformer I think). You may also want to uprate your HT leads. You may have to fit a 'Tacho Driver': some tachos don't like the signal that the points give out after conversion, and the MSD driver is there to cure this. I used the same spark plugs after conversion, with standard gaps. Installation took a couple of hours. As you have a conventional system, worth retaining the original stuff in the car, and do any wiring to enable you to revert to original should the MSD give proplems: shouldn't though, they seem pretty reliable.

HTH

[Nick Moss]

I have had high rev spark problems with 2 '68 911s recently, both cured by fitting the '69-on Bosch CDI system. The tachos needed modifying to take the CDI signal. The Bosch system is very similar to the MSD system and I would recommend any early system be upgraded.

[Barry]

Is the mod done on the tacho itself, Nick, or via an external unit?

[hot66]

my new '67 has an MSD fitted

[Nick Moss]

Is the mod done on the tacho itself, Nick, or via an external unit?

There is apparently an easy mod with a diode, but I couldn't get any detailed info off the US BBSs. I have had a couple of tachs modified.

[Barry]

Hmm, thanks Nick, I'll have to ask my friendly electronics wizard exactly what is going on with these tachs. He certainly grasped how the 'tacho adaptors' worked as soon as he saw mine, so is probably a good place to start.

Would obviously be helpful to the various SWB owners if we knew exactly what needs to be done, and whether it's DIY'able.

[chris68]

Hi,

Thanks for all the info, very interesting. It looks like I should do something to mitigate future ignition problems.

I have a lumenition kit which I took off a previous car. Does anyone know whether these provide any improvement to an early Porsche at starting and high revs?

The lumenition can be used with the original ballast resistor and coil setup. As far as I can make out, it isn't a capacitor discharge unit, but works in the convention way by halting the current in the coil primary to create the high secondary ignition voltage.

Cheers,
Chris