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Ignitition questions

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Morris

Morris

Yoda
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My car is not getting the gas mileage that I think it is capable of, and I believe spark may be a factor. My spark seems kinda weak to me. I am used to seeing spark that pops so hard you kinda feel it in your chest. Mine seems kinda dull and insignificant. My start-ups are a little harder than they should be, and my idle is rough.

My ignition set up is a bit... errr... unconventional for spridgets. I have a locked distributer (no mechanical or vacuum advacne) with an optical pick up that triggers 70 before TDC. The my spark advance is computer controlled and based on a RPM/Engine Vacuum table. I don't have any kind of amplification. I just have a coil that is grounded by a relay in my ECU computer.

What I am wondering is what is the best way to increase my spark output. Are the high performance coils (ie. MSD Blaster 2, ACCEL Pro, etc.) sold by most parts store worth the investment. Or are they basically a bunch a pretty decals on a plain ol' coil?

I would like to buy a Mallory CD Multi-spark system, but I am also wondering if there is something simpler and cheaper I can do to give me a hotter, better spark.

Any thoughts/opinions/words of wisdom?

thanks.
 
Hello Morris,

"I just have a coil that is grounded by a relay in my ECU computer."

The points set up in the distributor are more than just an operating contact. The capacitor across the points is necessary to give a decent spark so if you don't have one across your relay contact I would suggest trying that first?

'Sports coils' do give a higher voltage but still need a capacitor.

In my opinion upgrading the ignition system with modern high output electronic systems are not a noticeable improvement in driveability as most cars of this era are not so critical of spark intensity as modern engines that run weaker mixtures.

Alec
 
Morris:

You don't have the polarity reversed on your coil, do you?

Also, some original (Brit-type) coils have a ballast resistor built-in while other systems use an external "ballast wire" or resistor. Be sure that you don't have your coil double-balllasted.

For the record, I went to my local discount auto part store and bought a standard 12V coil for a '66 Chevy along with a generic ballast resistor. This is fired by a Pertronix ignition module (sitting under the cap of a stock-looking Lucas 25D distributor). All of this cost me just over $100 USD and it makes a spark that you could almost weld with.
I run my carb very "fat" (rich) for power, but I never have fouling problems.
I am running an old-style, side-wire distributor cap (because I think they look cool) and solid-core, copper secondary wires (Bonus: These wires are good for killing annoying cell phones).

One thing: I have my ballast resistor running through the coil 100% of the time...even when cranking the starter. Technically, this gives a weaker spark during starting (due to reduced voltage available) but it hasn't been a problem. I did it this way just to keep things simple.
 
Nial,

I basically copied you on my ignition set up (minus the Pertronix trigger).

Alec,

My car is fuel injected, so I am running mixtures closer to a modern car. How does the capacitor (condensor?) circuit wire? Is it just inline between the points and the coil (-) terminal?
 
I was going to ask about your ignition setup. Is it actually a relay... or is it a solid state device? Most electronic ignitions, even mapped ones, use solid state firing and it's my understanding that they have a certain amount (less than on a points ignition) of capacitance built into the circuit.

IF your system has no capacitance, I'd start with that as Nial suggested. All that should be required is to buy a condenser for a points type ignition and wire it in. The condenser shell gets connected to ground and on a negative ground setup (which I assume you have) the condenser terminal with the wire on it goes to coil (-). I believe these condenser/capacitors are typically rated for about 23 microFarads. I believe that electronic ignitions typically have about half that value built into their modules. Dave Russell would probably know for sure.
 
I think that's 0.23 microfarad (uF). My Haynes book gives 0.18 to 0.23 uF for all non-electronic ignitions.

You shouldn't need a larger coil to get a decent spark--if the spark is weak, there is something wrong, and that should be fixed first. If you are using a conventional ignition (except for the computer control, of course) you definitely need a capacitor. If you haven't been using one, it's likely that the relay contacts are fried.

The conventional wisdom is that the capacitor prevents excessive arcing at the points--but this is only half the story. It also causes the current in the coil to be AC, at a frequency of about 10 KHz. This is essential for getting a high voltage at the coil output--it is, after all, a transformer, and transformers need AC for a continuous output, even for a few milliseconds.

As for timing, that may or may not be a problem, but the strength of the spark is independent of timing. I don't know what kind of relay you're using, but it will take at least a few milliseconds to open, after your computer tells it to. This constant delay has to be included in the timing, especially at high speeds.

I'd love to hear more about your setup. Is this your own design?
 
Awesome info guys. Thanks.

The design is not my own. I am using a Megasquirt ECU with the Megasquirt and Spark Extra set-up. The trigger is from an Optroninc system.

The car had been running really rough lately so I did a compression check this morning. 150-150-145-100. Doh!

It may be a bit before I get a chance to experiment with my ignition set up.
 
Can you do a leakdown check? If not, squirt some oil into the low cylinder, if the psi goes up you have a ring problem. if not it's probably the valves. If you can do a leakdown just listen through a small hose like you would use to synchronise the carbs. If you hear air from the breather: it's rings, from the exhaust: the exhaust valve and from the carb: it's the intake valve.
 
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