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Ideal ignition for the TR4?


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Rather than jump into a pre-existing, on-going thread on the subject of ignition systems I thought I would start on new one, specifically about Capacitive Discharge Ignition (CDI). This is one of the earliest forms of electronic assisted ignition and improves the performance of the standard points ignition system, aka Kettering or Magnetic Discharge Ignition, while maintaining some of the simplicity of the earlier system. The Kettering system generates a high voltage spark as needed but the main drawback is that the points erode over time and need to be adjusted or replaced. The early CDI systems use the points as a breaker but promise to greatly extend the life of the points and the spark plugs while improving spark performance. The early system usually incorporate a switch to allow one to disable the CDI and return to normal function. 

There is a paper that explains this in some detail to be found on Paul Anderson's excellent TR4A site:  http://tr4a.weebly.com/uploads/2/1/9/8/21980360/capacitive_discharge_ignition_vs_magnetic_discharge_ignition..pdf

I have taken the liberty of extracting the pages that directly discuss an "ideal" CDI system using the old Hyland Delta Mark 10 box which can be readily found on eBay.

Fred Winterburn, whose father invented the CDI system, also makes his own improved version, but it is quite costly: http://www.capacitordischargeignition.com/

See also: https://mgaguru.com/mgtech/ignition/ig207w.htm

These CDI systems are attractive because they seem to offer improved performance without the sudden failure mode that is often experienced in some of the aftermarket systems. I am a civil engineer whose knowledge about sparks doesn't extend much beyond an analogy to water distribution systems but I know there are knowledgeable folks here whose opinion I would value.

Andy Blackley

TR4-CDI-Ideal-System.pdf

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Edited by Andy303
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The system as you say has been around for many years and is switchable in the event of a perceived failure.

This type of kit I used to sell/fit and ran a Triumph 2.5PI with one fitted for 10 years without problem.  Had to adjust the points when the heal of the cam follower wore, to keep the timing correct.

https://sparkrite.co.uk/electronic-ignition-kits/

Today I run Pertronix on the TR3A and have had good experience with it since 2010.

https://pertronixbrands.com/pages/pertronix-ignition

Cheers

Peter W

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Ask yourself - if CDI was so good why wasn't it more widely used, and why did the alternative of electronically-triggered Kettering become dominant in that market?  Cost-benefit perhaps?

The 'improved performance' the first paper describes at great length is electrical performance in terms of spark energy but if the standard spark is capable of properly igniting the fuel there is no benefit gained from increasing the spark current. There is no evidence presented that this translates to any better performance of the engine.  

Up to the rev limit of a standard TR, electronic systems only out-perform points if the latter are not properly maintained and adjusted.  The performance of the Kettering system does fall off at high revs, particularly for a 6-cylinder engine, because the dwell time becomes too short and proper adjustment becomes more critical, so for high-revving engines it may be useful - but those are not standard TRs.   I question whether you would notice any real difference in normal road use over a good standard system. 

 

Edited by RobH
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Back in the 70`s when I use to race Jaguars to be able to maintain peak RPM we all ran Sparkrite units and the difference was very noticeable as you could switch them in or out on the side of the unit plus it also had a kill switch which could be used as anti-theft device. I think I still have one somewhere but never used on the TR as I have a DD rebuilt dizzy . 

Stuart.

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The main advantage I found in moving to an electronic ignition system on a TR was the elimination of pre-ignition caused by the very low octane of fuels available in California in early 1980s. (I had taken my TR to California, and have since moved back to the UK with it). I like the predictability of ignition from using an electronic system, and I am still using the same electronic ignition I bought and installed in 1984. It has never let me down.

 

TT

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12 minutes ago, stuart said:

Back in the 70`s when I use to race Jaguars to be able to maintain peak RPM we all ran Sparkrite units and the difference was very noticeable as you could switch them in or out on the side of the unit plus it also had a kill switch which could be used as anti-theft device. I think I still have one somewhere but never used on the TR as I have a DD rebuilt dizzy . 

Stuart.

I still have a Sparkrite 2000 unit on my TR6, it was fitted in 1982 and is still going strong. Probably only 2 sets of points in all that time.

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I also at one time ran a Sparkrite unit with a switch to revert to standard.  I did have TRouble with it, repaired a few time (it was always certain transistors which failed).  I am now more than happy with my Accuspark hall effect unit.

Bob.

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I should clarify that the photo of a TR4 in my post is not my car but was taken from inside the article I posted. It is the TR4 of that author.

 

The Sparkrite people make similar claims as the paper. Is it CDI or Hall effect? The description on their website is not clear: http://www.accuspark.co.uk/sparkrite.html

 

I am currently using an unassisted distributor rebuilt by British Vacuum Unit, our equivalent of the DD : https://www.britishvacuumunit.com/

 

I suppose one of my misgivings about the Mark 10 is the sheer size of the thing. How large is the Accuspark unit?

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Sounds like the Sparkrite is now an electronically switched kettering system but perhaps the ad writer doen't really understand it ?

Quote: The Sparkrite SX4000 diverts the main flow of current away from the points and earths the coil through a relay .  (!)

By the way, Hall effect or optical switching are not related to whether the ignition is Capacitor Discharge or Kettering. The switching method merely replaces the points and can be used with either of these systems.  

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13 minutes ago, RobH said:

The Sparkrite SX4000 diverts the main flow of current away from the points and earths the coil through a relay .

Yep, that is correct as I understand it. It is probably a solid state relay. The points only act as the trigger, carrying a very small current then the relay closes to discharge the LT coil producing the HT.

Mick 

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Andy, +1.

When I bought my TR4A, it had a Pertronix distributor installed by the PO. It ran fine for several years, but this Spring, the mechanical advance failed (tore itself to pieces actually). So I purchased a refurbished stock dizzy/points from British Vacuum Unit. After dialing in a little extra advance, the car has never run better!

Jim

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16 minutes ago, Mick Forey said:

 It is probably a solid state relay. The points only act as the trigger, carrying a very small current then the relay closes to discharge the LT coil producing the HT.

Yes Mick- that's how all these points-driven things work but it is very unusual to call the switching unit a relay and usually it is just some sort of power transistor.  Using a relay would imply galvanic isolation between the switch and the output but why would you need that ? 

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I have been using a Newtronic/Piranha electronic ignition system since 1983.

Only modification has been to rub a few thou off the underside of the (Distributor Doctor) rotor arm to accommodate the thickness of the disc which chops the beam of the detector unit.

The small box containing the electronics is mounted on the vertical surface of the bulkhead, above the fuel pump and beneath the wiper motor.

The system has been utterly reliable.

Ian Cornish

 

 

 

 

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CDI can have drawbacks if done badly, but has several advantages if done right regardless of what is used for the trigger (points or whatever). Inductive ignitions have a horrible phase lag between voltage and current so the voltage has to rise much higher to provide the required current for spark breakdown. This results in a large voltage overshoot, and a less powerful spark due to the fact that current and voltage are so out of phase with each other.  CDI has a leading power factor with current rise actually peaking before voltage peaks but with the two being closer in phase (much closer than inductive ignitions). The total peak voltage and any overshoot as a result is determined by the voltage the capacitor is charged to, times the turns ratio of the coil. Since the power is higher (due to a favourable phase angle) high voltage is not needed for spark breakdown. Secondly, the leading power factor makes a CDI almost immune to a shunt resistance since the spark gap prior to breakdown behaves like a capacitance which prefers a leading power factor.  It's for this reason, not a fast voltage rise as is universally written (except by me) that makes CDI so great at firing fouled plugs or firing the spark gap with other shunt resistances such as wet plug wires or wet and dirty spark plug insulators. Here are a couple of articles explaining voltage overshoot and one explaining the real reason for CDI superiority in firing fouled spark plugs. At some point I will re-write the article into one article with phase angle being the common reason for most of the differences between CDI and inductive ignitions. It explains both the voltage overshoot to some extent and also the ability to overcome shunt resistances that would otherwise lead to no spark at the plug gap. Fred 

CDI Superiority in Overcoming Shunt Resistances.pdf Ignition Voltage Overshoot.pdf

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