Ignition systems

Quote from: 65bug on February 20, 2013, 16:25:59 pm

Can these magnetos be fitted with electronic ignition? I don't know too much about them, seems anyone who has one really likes them!

Based on your current combination I assume that you're running a street car.

Some magnetos have the option of electronic pickup (some Mallory Super Mag models). However, there is little to no need for electronic triggering in a mag.

The main reason for electronic triggering is reduced maintenance. But mags aren't as hard on points as conventional ignitions are. For one, since they don't see any power until the engine actually starts there's no opportunity for electricity to arc the gap if it's very small during the period when the ignition is on and until the engine actually rotates. Mag points last a long time, especially given the limited-use application that most mags see. I have mags that were made in the '60s that still have the original points in them.

The secondary reason for electronic triggering is increased coil saturation. It's tough to saturate a coil at high speeds on a V-8 engine when dealing with only 12 volts. Most conventional ignitions don't suffer that problem on four-speed engines. A magneto doesn't suffer that problem at all. It generates its own electricity and saturates the coil at way more powerful voltages than the vehicle's charging system.

Advance curves aside, a 'trick' ignition won't make any more power than a normal one will, at least on a car running street-type compression and speeds. Very high pressures and combustion turbulence can blow out the candles, so to speak. But that's in very extreme circumstances, think 13:1 and 8,500rpm. The advantage with a mag or a capacitive-discharge ignition is that it produces sufficient energy to strike an arc under those circumstances. So unless you're operating in extreme ranges you'll never benefit from the advantages.

Mags have significant advantage over capacitive-discharge ignitions by the way. A CD ignition produces a very high-voltage, low-amperage spark. The spark has enough pressure to maintain an arc under adverse conditions but because it has low amperage it has very low energy (low heat). A magneto, on the other hand, produces a spark with more voltage than a conventional ignition and far more amperage than just about any conventional ignition, at least at faster operating speeds. Heat is what lights fires, not pressure. You need just enough pressure (voltage) to maintain the arc under adverse conditions.

Mags have some pretty significant shortcomings for street-driven cars. To work best they need non-resistor wires and plugs. So forget about running a radio. The advance mechanism consists of a stack of brass plates rather than springs and counterweights. It's really crude--it exists primarily to let the engine fire at low advance. Once it gets up to speed the advance kicks in rapidly and completely. It's almost like a switch--static and full advance. So if you run a cam that produces a lot of pressure at mid-range speeds (like most street-driven cams) then the engine is more prone to detonate at mid-range speeds. Race cams usually trade off low-speed pressure for high-speed operation and the pressure they bleed off down there makes the engine less prone to detonation at slower speeds.

Plus Volkswagens may impose another limitation. Some say the brass distributor-drive gears VW used aren't up to the task for high-speed magneto use. Remember, the magneto produces more power at higher speeds which translates to greater resistance in the magneto. The industrial engines that use mags don't operate at very high speeds. They also have advance mechanisms that are tailored to their limited operating range.

You more than likely already have the very best ignition for your application. You're leaving a lot of performance on the table if you're still running the advance curve that Mallory gave that distributor. The default curve is very long and comes on very late to make good power for most applications. A short advance that comes in relatively quickly will really wake up an engine. A magneto would likely be nothing but eye candy for your application.