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MG MGB Technical - Electronic ignition performance

Hi all.

I'm the owner of a 73 BGT, overbored to '040, lightened flywheel, fast road cams (not that wild) and K&N airfilters.
The car has still the standard ignition system.

If I change it to an electronic ignition system (Lumenition or similar) will I get a performance increase, or the advantage will be just a maintenance free system?


Thanks, Valter.
Valter >99 VVC & '73 BGT<

Maybe a little performance increase, if your distributor bushings are worn, but mainly it will free you from points maintanance. RAY
rjm RAY

Valter. Neither, in truth. The one test that I have seen which was conducted in a scientific manner, under controlled conditions, showed no performance increase due to the use of an electronic points replacement system. The Lucas distributors were designed to be maintained (cleaned, inspected and lubricated) on a annual basis and this must be done if the distributor is go continue working as intended. Ideally, this is done by pulling the distributor from the block, carefully mounting it in a vise, and doing the cleaning and lubrication at that time. I consider removing the points plate highly desirable because it allows me to see the mechanical advance weights and it allows me to inspect and lubricate the sliding portions of the points plate.

Installing a new points set and condenser is a minor portion of the annual cleaning/inspecting/lubricating process and actually easier to do than to remove and reinstall the points replacement system.

Les
Les Bengtson

The electronic system definitely gives a smoother idle but mot much else. I had two systems a Lumenition Magnetronic system on my GT which has been troublefree for about ten years and the one on my roadster which I obtained off e-bay from Simon Lawther the first one of which did not work. The replacement worked for about six weeks and then failed most embarassingly on the MOT ramp. Even this one when working gave a noticably smoother idle but nothing else.
Iain MacKintosh

Whilst any distributor will need the regular maintenance mentioned by Les, ignition performance from points will deteriorate slightly over time whereas that from an electronic trigger won't (normally). This is why North American spec MGBs had electronic ignition from the mid-70s whereas UK and others didn't, they were required to go 50k miles and stay in spec without any adjustments, even though that is way over what any reasonable owner would have asked it to do. An electronic trigger won't give you noticeably better performance over correctly adjusted points. Some claim that electronic triggers avoid the inevitable voltage drop that occurs with points contact resistance, in fact the reverse is true. Electronic triggers lose 1v which is why American spec coils were 5v instead of 6v. Even a set of old points I had only lost 0.08v, 0.27v was being lost in the wiring to and from the points i.e. only 0.35v in all, which is still there with electronic triggers. Good quality points are nowhere near as bad as people make out, last year I changed them in my roadster and V8 after about 15k. Since changing to checking points by dwell instead of gap adjustments are very rare indeed. The roadster ones hadn't even needed any adjustment in all that time, staying within the wider tolerance of the 45D distributor. The V8 had required one tweak to bring it back within dwell spec as they have the narrower tolerance like the 25D. I only changed them as the roadster was starting to take a couple of seconds longer to fire up than normal, there was no change on the V8. If you check gap rather than dwell then you have to make sure there is no spike and hole first, and by the time you have dealt with that you might as well change them, which is why some people may complain about them. Quality of replacements is the big issue, Unipart or ideally NOS Lucas are good, some no-names seem to wear down the heel very quickly.

The drawback of electronic is that whilst in general they are more reliable, when they fail they usually do so suddenly and completely, and substitution is the only diagnosis. Points usually give some warning, can usually be dealt with at the roadside, and are cheap to carry (with a condenser) as a spare. I've never had points or a condenser fail in 40 years. Some no-name magnetic triggers are crap, moving the spark point so much it occurs off the cap contacts, and even the named varieties move it more than I would expect.
P Hunt

I had a Piranha electronic system in my 1971 daily driver MGB for over ten years. This system has an optical chopper and is now sold as Newtronic. In all that time I never touched the distributor and the system never gave me a moments concern. The car started well, ran well and gave good fuel consumption. Yes I know the dissy should be maintained, but I'm basically a lazy guy and it was working fine, so I left it alone. As Paul says, when they fail, they do so completely, but I think failure rates are low. But don't expect a power boost.
Mike Howlett

This is slightly off subject but closely related. Anyone got views or opinions on CDI or multiple spark systems ? Barrie E
B Egerton

I had a capacitive discharge (if that's what you mean by CDI) unit in the early 70s. It was a Sparkrite I built as a kit, and don't laugh but it was triggered off the points. You could switch it between conventional and electronic, it didn't make any difference that I could tell so although I took it off that car I never bothered fitting it to anything else, and it is still in a garage drawer.

The fancier and more modern systems are suited to triggering very lean mixtures and so do make more of a difference there, especially in adverse conditions.
P Hunt

Hi Barrie,

Like Paul I had a home built CDI from the early 70s to the early 90s, built to a Wireless World design. It worked in two cars (Morris 1500 OHC and VW Golf) with a total life of nearly 20 years. It was triggered by the points. It was recommended that the plug gaps be opened to 40 thou, to give a better chance of firing the fuel, as the time of the spark was much shorter. Being lazy I didn't check the gaps very often, and when I did they were at 80 thou +, but no noticeable problems.
I found that cold starting was much better, and required far shorter times on choke. No noticeable difference in fuel consumption or power, though articles at the time quoted up to 10% greater power.
Sole maintenance was an occassional tweak of the points gap, to make up for heel wear, which showed up as increased fuel consumption. Points lasted forever, due to the low current switched, into a resistive rather than inductive load.

Silicon Chip has recent updated multi spark CDI and programmable trigger articles and kits. Google Capacitor Discharge Ignition to find the articles.

Herb
Herb Adler

When you read the blurb on capacitive Discharge ignitions it all sounds very attractive, but in reality provides very little. First of all the Multiple spark only occurs at lower revs, when the coil has more recovery time anyway, and although the spark energy is greater, the spark duration is shorter. So at higher RPM when the ignition system has to deliver faster, you still get one spark but it has a shorter duration. Doesn't seem like you get a great deal for your considerable wedge!
Personally I'd go electronic every time, just for it's consistancy and ability to compensate for shaft wear, but then again I have never been let down by one......yet! I should also imagine that they can switch faster than a points set up, and provide a fatter spark at high revs, but whether that leads to better combustion, I can only guess. And, it has to be said, the V8 engine tuners seem to prefer the Mallory twin point dizzy!
Allan Reeling

Twin-point is even more of a waste of money, especially for 4-cylinder cars. The V8 can deliver twice the sparking rate and Jag V12 three times at peak revs not much less. The factory used dual point in the 20s and 30s for some of their record attempts, but those engines were very different. The V8 with standard ignition revs far too easily into the red, unlike the 4-cylinder. I've never reached the orange in mine, acceleration is obviously tailing off and there is all that noise which makes me cringe.
P Hunt

This thread was discussed between 12/01/2010 and 15/01/2010

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