Digital Igntions...

[pyro883]

never really understood anything about them...What do they do? Does it help timing?

[truckster]

If, when you say digital, you're talking about HEI, the advantages are that you have higher voltage/ hotter spark and since you eliminate the points, far less maintenance.

[pyro883]

I was really referring to products like MSD

[Billla]

"Electronic" (capacitance discharge or CD) ignitions overcome the recovery time limitations of a standard ignition coil.

A coil consists of two wire coils, one inside the other. The outer coil connects to the distributor points, the inner coil connects to the central tower on the distributor. It works by creating a magnetic field in an outer coil when the points close putting current to the outer coil, then when the points open power is interrupted to the coil and the field "collapses" which creates a high-voltage spark in the inner coil...which is then distributed to the spark plugs. 12V/high amps in, 30,000 volts/low amps out...it's physics and it's called "induction" - the two coils don't actually touch.

At higher RPM, there is insufficient time for the outer coil to build up a full field, so the field is weaker...and therefore so is the spark created in the inner coil. The better the coil the higher RPM the coil is capable of sustaining, but this is typically advertised as creating a "hotter" spark - like 45,000 volts. What they're not telling you is that the reason they create a hotter spark is to make up for how quickly it degrades at high RPM...45,000 volts at 3000 RPM may only be 16,000 volts at 5500 RPM.

A CD ignition takes over to augment the spark the coil produces when it starts to fall off by using a capacitor to store energy...as the coil delivers less voltage, the CD ignition fills the gap so we have that 45,000 volts all the way to redline.

The benefits are primarily seen at high RPM (above 5500) but the hotter spark can produce benefits at highway speed and has shown to slightly improve milage.

An HEI experiences less RPM fall-off due to the design of the coil and that the coil output is directly connected to the rotor vs. having to go through a wire. Generally the stock item works well to about 4500-5000 RPM, the aftermarket items (MSD, etc.) go to 6000+.

Generally, an HEI is your best bet for a daily driver and a CD ignition only if you expect to run regularly at higher RPMs.

My $.02

[pyro883]

sweet explains it a lot better for dummy me. I have an HEI now and its just going to be daily driver/street rod deal.

[72lb4x4]

Good explanation Billla!

[WorkinLonghorn]

If I can butt in here with my own "dumb question", this is the part I don'tunderstand;

The benefits are primarily seen at high RPM (above 5500) but the hotter spark can produce benefits at highway speed and has shown to slightly improve milage.

If your plugs are gapped at say .045" and you're cruising down the hiway at 2500 RPM and it takes 9,000 volts to jump the gap,then what benefit is a "hotter" spark,how is it different? Is the spark broader,or last longer or what? And with coils claiming 60,000 volts,how come I don't hear about people running .060+ gaps? Thanks-Brian

[Billla]

Originally Posted by WorkinLonghorn

If your plugs are gapped at say .045" and you're cruising down the hiway at 2500 RPM and it takes 9,000 volts to jump the gap,then what benefit is a "hotter" spark,how is it different? Is the spark broader,or last longer or what? And with coils claiming 60,000 volts,how come I don't hear about people running .060+ gaps? Thanks-Brian

There ain't no such thing as a "dumb question" - any knowledge I have came from asking those same questions And some of this question is beyond my theoretical (vs. practical) knowledge, so I welcome comment as always.

You're absolutely correct that if you've got enough voltage to jump the gap, more isn't better. A wider gap - requiring a stronger spark - improves combusion efficiency somewhat and so offers some improvements in economy.

The issue is still the recharge time, but as noted there's no significant benefit to CD ignitions or aftermarket stuff unless you're turning higer R's...which is why the HEI is such a good deal for 99% of us.

Since the racers are going to find this thread sooner or later, it becomes a whole 'nother question when we factor in NOS, 12:1 CR, race gas, etc....the thread here is focused on engines making <= 1.2 HP/CID.