Dizzy options

[Richb77]

All.

I have a choice between a couple of dizzys and wanted to understand the advantage of one over the other (other than cost).

Option A is a Lucas 43D Fully electronic (no points)

Option B is the same but a (upto 3 times the spark power) and 30 quid extra.

Is the extra spark oomph worth it for a mildly tuned 1600 Xflow? (GT spec plus a couple of horses).

Cheers you lovely repository of important knowledge.

[Graham]

You need enough spark, more give no benefit, in fact its more likely to leak away if cap, rotor and leads are anything less than 100 perfect. i see mo point in paying the extra

[Richb77]

Thanks Graham. Sound advice as always!

[Dyno]

Do you really think they can get 3x more energy into a spark as the one already supplied by an OEM electronic ignition?

Most give a max off approx 130 Kjoule and as far as I know it is the max they can supply because more is deadly and not allowed by laws. In F1 they used to build "deadly" ignitions but I think also no longer allowed for many years. Maybe some drag racers still got this kind of ignition.

The only "better" ignition available is Capacitive ignition. It does not supply more energy but start the fire at a higher voltage and can fire instant, without waiting for coil charge like inductive. This means very high RPM's possible even with 12 cylinders and distributor. They can also fire wet plugs. Reason why Porsche had it as original equipment in the 70thies. They where prone to wet plugs at cold start with contact points. Today with electronic modules it is no longer an issue but capacitive like MSD still do better. The original capacitive ignition from Porsche is even weaker as today inductive ignition but, the spark does nog drain away over the wet plug like it can do with inductive, just because they always start he fire at high voltage. (inductive still has to build up the voltage and as soon as it find a leak it drains away)

[Miniliteman]

Dirk,

think Rich is talking about a system like the Aldon Ignitor I (option A) and an Aldon Ignitor II (option B).
The first is just an electronic transistor replacing the points. The second has an additional current (coil-current) control circuit with a special low ohm coil so that the coil gets "charged" over a wide rpm-range. At higher rpm the coil energy with option B is alot higher than with option A.

As to energy think you have a typo there, as a good spark energy is approx. 130 milliJoule (not kiloJoule).

The capacitive ignition is a good choice on an engine with very high compression and alcohol fuel as it delivers one big bang despite fouled plugs and high pressure (dragracers). On a more normal engine this type of ignition has a big drawback.
If the ignited mixture is blown out by a lean mixture or good swirl that's it, the mixture will not ignite again. (the high voltage spike is high but also short). With a normal ignition system when the mixture is blown out the energy still stored in the coil will re-ignite the mixture. We did a comparason once on a high power Pinto engine, MSD 6AL compared to a Lumenition system. No difference between these w.r.t. bhp.
My advise always is if you have a DGAV or similar carb use the cheaper system (like Ignitor I); if you have twin carbs like 45DCOE's use the Ignitor II.

Regards, Leon.

[Dyno]

OK, now I see, but I use the "standard" kind of contact point replacers with 1,5 Ohm coils, this will supply a real big spark, about the same as the one that does control the dwell. Only drawback is, if you leave contact on for little too long, it will take the coil and sometimes also the module.

Totally agree and also did the same test. We used a good tuned engine and there was totally no difference in power between the most expensive spark and the one from a cheap contact point replacer. As Graham already said, you need a good spark to ignite the mixture, the rest is spare energy. We did the test after I found a lot of standard VW T1 engines came in with stupid expensive MSD distributors and boxes (was approx 1000 € at the time of the test) and I found it was silly to spend so much money at the wrong place.

MSD does fire more than once at low RPM, just in case the first spark did not ignite the mixture. I do not recommend anything less than just what is needed and only use MSD kind of ignitions if I know it is safer as a normall ignition. My Rover V8 engine has capacitive ignition and distributor (because I also have turbo in mind).