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MG MGB Technical - Mallory Unilite vs 123Ignition

Anyone know which is better for racing. I need to upgrade my Aldon Distributor to one of these units.
Thanks Andrew
ASH Andrew

123 is has fixed curves, but 16 of them. The Unilite (I think) only has one curve but you can swap springs around and tweak them to get different curves. If one of the 123 curves is right for your application then that will be easiest, if not with the Unilite you should be able to tune the curve to whatever you need.

And that's the crucial point - what curve do you need? You will have to put the engine on a rolling road and determine the timing that gives best power for full throttle at, say 500 rpm increments. Only then can you start on which distributor is best. Much easier to do for a vacuumless distributor, which is what you should be using for competition anyway

Another alternative is an electronic advance module that the MGOC used to sell that allowed you to select the advance at intervals, used in conjunction with a distributor without either vaccum *or* centrifugal advance. Gives the flexibility of the Unilite with the ease of the 123. Even better would be knock-sensing, then you wouldn't even have to both with the rolling road.
Paul Hunt

Ash you ask about a distributor for racing. A racing engine usually uses a short advance curve, usually all in by 2.5k. When on the track the revs when it counts will always be above the curve and on full advance anyway. Most of the reports on the 123 for street and racing have been good. Peter Burgess reported higher dyno results with the 123 which you would have to put down to a more accurate and better quality spark as advance curve will not affect peak power.
DENIS4

Not sure about the 123 spark being more 'accurate', it actually jumps at 500 rpm increments or so rather than being the smooth curve which you should get with mechanical.
Paul Hunt

If you have a look at the data on the 123 from Peter Burgess's site http://www.mgcars.org.uk/peterburgess/123GB4RV.pdf
you will see that advance reaches a maximum well before a race motor will be developing max power

The details on the last sheet are usefull in that it gives an indication of the charateristics of each curve so you can choose one initially that should be close to what is needed for your engine

John Turner
John Turner (Midget & MGB)

Andrew,

although i do not know the mods done on your engine, i made the best experiance with a d45 set to the specs of the old Abingdon Special Tuning dizzy. I think you should contact Jeff at Advanced Distributers and ask him for some adwise. 0
The 123 is a potential problem on race engines as it is not capable to coope with the extra temperature that stage tuned engines will produce and it is mentioned to substitue all the stock dizzys only but not those of engines in race tune.
I have no data upon the Aldon dizzy and never had one on my test bench. Others that have used it did not have any problems with it, so it seems to be very close to the ST dizzy specs, as far as i could compare the state of tune and the perfomance of the cars fitted with an Aldon.

For cars that do not log that many Miles as a daily driver, points should be your choice as the electronics might become problems with the heat under competition conditions. I had this once just after changing from point and rechanged again. No probs anymore since.

Cheers

Ralph
Ralph

When I spoke of the accuracy of the 123 distributor I was referring to the phasing of the spark which is a weak point with some dizzies. Ash had requested our thoughts on a racing distributor which will be on full advance at all times when competing, or should be.
DENIS4

Poor phasing, which is where the rotor moves away from the cap contact at one extreme or the other of vacuum advance is a known problem with after-market triggers when fitted in place of points. This problem only occurs with vacuum advance, with centrifugal the relationship between rotor and cap contact is fixed. I'd sincerely hope that the designer of the 123, or any other *distributor* (i.e. includes both trigger and mounting plate) wouldn't make such a fundamental error even with vacuum advance phasing, let alone static phasing. A competition distributor wouldn't normally have vacuum advance.
Paul Hunt

Well here is my 2 cents. I would go with a MegaJolt system. Its more detailed, precise and also cheaper.
james

If the regulations of your racing allows it then EDIS, with either a Megalite or megajolt controler would be a good option. It gives you complete control via a programable 3D map. See http://www.kewengineering.co.uk/upgrades4mgs/Electronics/index.htm
Mind you, I would agree with the observation that you will probably be at full advance most of the time anyway on a track.
I D Cameron

Phasing also relates to the spark occurring every 180 degrees crankshaft dead on, and not all over the place as many setups do. A crank trigger type would be good but usually not aloud in vintage,
DENIS4

This thread was discussed between 26/10/2008 and 12/11/2008

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