45 replies to this topic

[Dangerous]

Hardrevin, that's quite an assumption on your part too

To make it clear, Multi Spark Discharge systems are called MSDs. "MSD ignition" to me means any multi spark ignition system, whoever makes it, just like 'radial tyre' means a radial tyre, not a Bridgestone or a Dunlop tyre.

To clarify things more, or maybe confuse them more, the MSD (brand name this time) ignitions manufactured by Autotronics aren't all MSDs - the base model at least, which is still sold as a MSD branded unit is not an MSD. It's also only the top of the range MSD (brand) ignitions which are both MSD and CDI units combined.

[antelopeslr5000]

Beer, Chocolate lol...

The term 'MSD' is confusing. Dangerous IS CORRECT when he says not all Autotronic MSD ignitions are Multiple Spark, some are just CD ignitions (like the MSD Blaster Ignition) but the majority of Autotronic MSD ignition systems are a combination of Multiple Spark and CD ignitions (and not just the top end of the range systems either).

I don't know of any ignition systems manufactured today that are just Multiple Spark. I'm not saying they don't exist, just that I don't know of any.

Speaking of combining things... I had a chocolate flavour beer from Belgium the other day, a Floris Chocolat. It was quite unusual, it smells like chocolate, tastes like chocolate but I woke up the next day with a terrible hangover!

So try combining a Freddo with a VB when you get a chance Hardrevin'!

[Dangerous]

Bang for buck and reliability wise, have you considered using the later RB series or VG series power transistor unit (PTU) and the Z32 VG series direct fire coils, ie one coil per cylinder?

[Dangerous]

Some answers for Eddie.

First up, spark power. The job of the spark is to ignite the fuel/air mixture around the spark plug, so that the flame front (the outside of the burning ball of fuel/air mix) expands at just the right time to hit the piston when it's at top dead centre with enough force to push it down again. The spark does not cause all of the fuel/air mixture to explode at once - it starts small, around the spark, then spreads in a ball shape until all of the fuel/air is ignited.

If the spark is too early, the flame front (explosive 'ball' of combustion pressure) hits the piston before it's near top dead centre, wasting some energy, and causing knock. If the spark is too late, the piston is already starting to travel down again, so the combustion pressure can't transfer as much energy to the piston, with a resulting loss of power.

There can be a problem with too much energy in the spark, where the spark actually pushes some of the fuel/air mixture away from it, instead of igniting it properly - a bit like if you try to explode too much TNT - some of it will detonate, but some unexploded chunks of TNT will be thrown outwards by the large force of the explosion.

Multiple sparks. On a standard ignition system, the single spark is quite capable of reliably igniting the fuel/air mixture. If you up the power of the engine by quite a bit though, by putting in lumpier cam, larger valves, more fuel, turbocharging etc, the fuel/air mix becomes more dense, and more turbulent. The dense fuel/air mixture is harder to ignite, and the increased turbulence can actually 'blow' the single spark out, just like blowing out a candle. Once it does this, the mixture cannot ignite, and a misfire occurs. By making the sparks multiple short sparks, if one gets blown out, it is replaced almost immediately by another one, so the mixture is still ignited. A multi-spark ignition system simply has a large number of smaller and shorter sparks in the same time period as a conventional system has one spark.

Hope that answers your qustions from post # 1

As for when you need upgraded ignition systems, that's got to be taken on a case by case instance, as it depends on how many of what type of mods you are making for an engine. As a very rough guide, if you are starting to experience misfires at the rev range where your engine seems to want to make most power, then you may have an issue with sparks breaking down.

Talking Holden 6s and 8s, in my opinion (and it's only mine, others will no doubt differ), the stock Commodore style electronic ignition systems are a good improvement for anything from standard motors all the way up to 'barely streetable', or where peak power is starting to be made around 4000 rpm and upwards. Usually at this point, the coils aren't big enough to supply strong spark at the increased redline. If you're using the car for drags as well as street, where you're obviously hitting the redline more, you might have more of a need to upgrade coil and/or ignition sooner, and seriously start to think about better plugs and leads.

[Tiny]

Brett: If youd have read the posts above, you would have seen that after 3000RPM there isnt enough time to have more than one spark.

CDI (Capacitive Discarge Ignition) is basically an amplifier for teh spark. Bigger brighter spark. Over 3000Rpm, you dont have time for more than one spark, but the bigger brighter spark from both the CDI and MSD systems are what makes them worthwhile!

Cheers mate.