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MG MGB Technical - Pertronix Ignitor II

Anyone out there using a pertronix Ignitor II on there MGB and if so what has been your experience? Also did you purchase the Flamethrower II coil and have you had any problems with it? Any compatibilty issues with a ballasted system that supplies 6V to this coil (.6 ohm)?
Frank

Frank,

I use the Pertronix II and the regular Flame Thrower 40,000v coil.

You can barely tell the difference between the Ignitor and Ignitor II, but The Ignitor II senses current levels in the coil and adjusts the dwell to maintain peak energy throughout the entire RPM range. Dwell time is increased or decreased with changing engine RPM and operating conditions. This provides more energy at high RPM reducing misfires while improving engine performance. Compared to the original Ignitor develops an average 3 times more available energy between 3000 and 5000 RPM and nearly doubles available plug voltage.

Flame Thrower 40,000v 3.0 ohms is designed for the Ignitor for optimal performance. Four cylinder engines require a minimum of 3.0 ohms of resistance. The Flame-Thrower II super low resistance (0.6 ohms) 45,000 volt coil.

Regards, Ray


Ray 1977mgb

The 6v coil, and ballast that supplies 12v to it, should both measure in the order of 1.5 ohms and not 0.6 ohms. As such both chrome bumper (unballasted 12v)and rubber bumper (ballasted 6v) systems end up as about 3 ohms total resistance, which is what is needed for points operation. However 12v Sports coils are about 2.4 ohms. With electronic triggers and full electronic ignition systems the coil resistance can differ greatly from this as the way they are 'fired' can be very different. But you will not see much difference in starting or running between a correctly maintained points system and any electronic system.
Paul Hunt 2

Paul....the new Pertronix Flame Thrower II coil is a .6 ohm coil and is recommended for use with the Pertronix Ignitor II set-up although not mandatory is my understanding. I must admit to being a neophyte when it comes to truly understanding all this. Perhaps you could visit the Pertronix website...read up on their blurb about this and enlighten me...you always have a way of making these things easier to understand. Thanks for your reply!
Frank

I thought the benefit of the Ignitor II (and the Crane XR-3000) was that they offered variable dwell which does help start the car faster and provide hotter spark at rpms over 3500, where points tend to bounce, dwell time decreases, and ignition timing becomes more critical.
Jeff Schlemmer

Electronic variable dwell triggers can use a very low resistance coil as they tend to send a pulse of energy into the coil of a consistent duration regardless of rpm, and none at all when the engine is stationary but the ignition on. By contrast points systems usually connect power to the coil as soon as the ignition is turned on as the engine usually stops (in one of two positions) with the points closed. This is one of the reasons that the currents in a conventional system have to be controlled by the resistance (e.g. the coil or coil + ballast). Even then it is a compromise, a coil will almost certainly overheat if the ignition is left on with the engine stationary for any length of time, as the currents are designed to be 'safe' when running and the average current and hence heating effect is around 60% of the stationary heating effect. If the currents were reduced to be safe with the engine stationary it would almost certainly compromise spark energy too much.

I'm pretty sure that some points *can* bounce over 3500 rpm, and one feature *can* help under certain circumstances, and another feature under others. And yes a good, new aftermarket gizmo probably *will* perform better than some ancient, worn and under maintained original item. Mallory dual-point distributors for example are sold on their longer dwell giving more consistent energy at higher revs. But when you consider the V8 dwell is half that of the 4-cylinder for almost the same peak rpms, and the V12 half as much again, any reduction in 4-cylinder coil charge time at peak rpms pales into insignificance. MG did use dual-point distributors in the 30s, but on high-revving competition engines. When you consider how crude the mechanical and vacuum advance mechanisms are, and how approximate to the ideal curve for any engine (even when fed with the original leaded fuel those curves were designed for) again I submit that any advantages of electronic triggers are marginal at best. I would have thought that the fixed 'on' period of a variable dwell system would have been way way shorter than the variable 'on' period of points at cranking speeds, and so cannot see how it contributes to starting as well as smooth running at the upper end.
Paul Hunt 2

The issue that is rarely addressed, is that the coil builds higher voltage the longer it is fed juice, up to the max voltage for that coil. But the coil virtually never develops full voltage as once it reaches a hi enough voltage the spark jumps and discharges the coil. If 3,000 volts is enough to jump the spark at the plug, the coil voltage will never exceed 3,000 volts, whether it has long duration or short. If the ignition system has a wide plug gap, and hi compression with a rich mixture, it might take 15,000 volts to spark.

Transistor switched ignitions provide more dwell than a stock set of points and are far more reliable. I don't know what difference "variable dwell" makes in the real world.

Barry
Barry Parkinson

Well, one great feature of the Ignitor II is that it senses the "key left on" situation and shuts down the system to prevent damage. It also increases dwell at very low (starting) rpms.

The Crane XR-3000 system has an LED on the ignition box that lights during spark. Its perfect for setting initial timing - turn the distributor until the light comes on and lock it down!
Jeff Schlemmer

This thread was discussed between 07/06/2006 and 13/06/2006

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