Electromotive Direct Ignition Controller & Coil Assembly (top), & Custom Distribution Manifold (bottom)

Direct Ignition and Tuning Equipment

as published in British V8 Newsletter, Volume XIV Issue 3, December 2006

by: Howard Fitzcharles

Distributor ignition is OK up to a point, but when you look at the drive of most distributors you will see a lot of free play between the piston position and whatever is in the distributor that actually triggers the coil. Whether it's a set of points, a light emitting diode, an electromagnet or whatever. Then you have to fire a coil, sending current to the distibutor cap, along to a carbon brush, then to a rotor, jumping a gap to a peg, and back out of the cap to a wire before it gets to the spark plug where it is trying to jump another gap to light a fire in the combustion chamber. Whew - what a trip!

Maximum horsepower, as far as ignition timing is concerned, occurs when ignition timing is advanced right up to almost the point of detonation. In other words, if you were to advance your timing slowly until you got detonation you would see horsepower increase until you reached an abnormal combustion (which is commonly misnamed valve ping or valve rattle). The trouble with detonation is that high RPM detonation is not easily heard, unlike the low-RPM-under-load detonation "rattle". With gear lash and timing-chain stretch causing loose play in the drive of a distributor, at speed the drive is bouncing back and forth so you must keep the timing slightly retarded to account for the variation in the actual timing. You have shorted yourself on power because you are forced to run a slightly retarded timing because of this "spark scatter" variation. An ignition that is triggered directly off the crankshaft is much more accurate and consistent.

Because a more consistent initial signal allows more timing advance, higher combustion chamber pressures are achieved. The final result is that the engine produces more power!

What about ignition timing through the RPM range? Most Kettering ignition (standard "points type") systems use a combination of vacuum control and centrifugal controls to get the timing close to what is needed through the RPM and load range. Here, they really get sloppy and - guess what! - as soon as you make any significant modifications to your engine you completely change the needed advance curve of the distributor. You can NOT guess what this new curve is. You will need a "distributor machine" to even change the curve. And guess what again! You may find it hard to even find one in your town. Call some repair shops and see. A race car shop will be your best bet. What curve is best for your particular engine can be different than another identical engine.

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What to do? It's simple: Direct Ignition! In a typical direct ignition system, a trigger-wheel is mounted on the crank pulley and a sensor (called a "pick-up") is mounted close to that wheel. Crank position, as sensed by the pick-up, is the basis for ignition timing. Direct ignition also uses a different coil strategy, wherein the ignition fires spark plugs directly from multiple coils and not through a distributor cap and rotor. Each coil has two spark plug wire terminals that are in turn wired to two conventional spark plugs. (One spark plug fires on compression while simultaneously the companion spark plug fires simultaneously on exhaust.) The advance curve is handled electrically; knobs on a control panel allow a user to dial in the advance through several RPM ranges. Using these controls, one can optimize the advance curve to match your particular engine. One of the dials is a rev-limiter adjustment. A MAP sensor senses manifold pressure changes, as another input to the electronic controller.

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I have selected an Electromotive brand direct ignition system for my Buick 215cid V8 engine. One thing that sets the Electromotive "XDI" system apart is the ability to charge multiple ignition coils at the same time. The resulting benefit is increased dwell time (up to at least sixty degrees and about 1000 microseconds). Unlike capacitive discharge systems that only put out one very short spark, the XDI puts out a fuller, longer-burning spark at high engine speed. The longer burn time assures effective burning of even lean or poorly balanced fuel mixtures. Full spark energy is available over the entire RPM range.

Electromotive Timing Controller     MSD Knock Sensor System

An optional timing control can be mounted inside the cockpit for fine adjustment of timing as conditions (such as temperature, fuel quality, etc.) change.

How do I know what to set the adjustable timing to? I use an LED display from a knock sensor system made by MSD. The knock sensor sends a signal to the display of LEDs. This way, no matter what the present conditions are, I can keep the ignition timing to an optimum by reading the LED display and setting the timing to it's optimum. The MSD knock sensor can read detonation and give me a display when I can not hear any detonation. This is especially true at high RPM. Detonation (abnormal combustion) can destroy an engine in just a few minutes of high RPM running.

If you are into fuel injection you will find that Electromotive has a cool system that handles fuel control also.

Another very practical tuning aid is called "G-Tech Pro", which is a computer that stores, analyzes, and reports the output of integral accelerometers over time. One use of the G-Tech analyzer is engine tuning: if you know the weight of your car and enter it into the computer, the device can calculate (wheel) horsepower based on the car's actual forward acceleration. I first saw one of these units in a friend's car a few years ago. (The "car" was a turbo-charged aluminum-block 350 Chevy powered Datsun PU.) My friend Oz had the engine on a dyno and knew what it should show as horsepower. We were impressed that the G-Tech numbers matched the actual dynomometer consistently.

G-Tech Pro has three accelerometers. One accelerometer measures lateral acceleration, which is very useful for tire and suspension tuning and driver training. G-Tech tools are a great tool for autocrossers!

A "z-axis" accelerometer measures up-and-down acceleration. This extra sensor provides a big technical advantage: G-Tech Pro can automatically detect and compensate for suspension lift or dive which would otherwise compromise accuracy.

The basic model, called "G-Tech Pro SS", currently costs about $199. The "G-Tech Pro RR" (which replaces the now-obsolete "G-Tech Pro Competition" model) can interface with a laptop computer. At about $299, this unit costs less than a few dyno pulls on an engine dyno! I used to race motorcycles professionally and didn't have such tools so I had to make estimates by timing high speed test runs on straight highway. (Much more dangerous than racing on a race track!) With a G-Tech Pro you can make all of your tests and not spin a wheel or go over the highway speed limit. Cool!

Check out Howard's website! MG's, Triumphs & Jaguars: www.mg-tri-jag.net

Disclaimer: This page was researched and written by Howard Fitzcharles. Views expressed are those of the author, and are provided without warrantee or guarantee. Apply at your own risk.

Photos by Howard Fitzcharles. All rights reserved.

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