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Advance curve for 1 2 3 distributor


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I am fitting a 123 distributor, any advice on which curve to select .

Martin you dont listen do you. B

Stuart.

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As Neil says the curev will be much the same as the 6. Because the 6 and 4 have similar combustion chamber shapes and size and compressions (and turbulence does most of the timing anyway) so we need similar curves. Like these:

http://phys.org/news/2015-03-million-migratory-birds-cyprus.html

Note these are disy degrees so at the crank they are double these values. All in the centrifugal swing gives about 28 ckdeg at 3000rpm. Add the static timing of around 10BTDC ( right?) and we have about 40deg advance at 3000rpm. For most old engines it will be around 35-40BTDC

The 123 has I think a vac advance facility, to connect ot the throttle edge take-off. That should advance the spark further at cruise , to give at 3000rpm about 45BTDC. This gives more more time for the less compressed, leaner mixture to burn correctly. So the 123 vac advance setting that adds about 10 to 15 ck deg is the setting to try first.

Peter

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FWIW if you do use the A/R facility if fitted on a 123 then you do need a flame trap or similar in the line as any excess fuel/vapour that managed to make its way into the dizzy will destroy it. Not applicable to standard dizzys.

Stuart.

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Read this thread page:

 

http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1380262350/

 

Then try the excellent 'MintyLamb' 123 Ignition Curver to see what is offered as steps 0-9 & A-F

 

http://www.mintylamb.co.uk/123ign.html

 

They all suggest a static of 10 degrees - where they go between that and full advance is quite interesting and worth viewing as a graph to compare with the orig spec.

 

This link gives a nice graph of the effects on rate of advance controlled by different weight springs in a mechanical advance system ( as orig)

http://www.setyourtiming.com/timing_settings.html

 

Cheers

Peter W

Edited by BlueTR3A-5EKT
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Spark timing summary:

http://www.innovatemotorsports.com/resources/myths.php

It mentions factors that affect optimum timing: rpm, compression ratio, load, mixture, cylinder filling. Most of which can be different from the original factory engines.

 

Measuring the best spark timing is difficult, if not impossible. The torque changes little for a big change in advance or retard from peak.

http://www.daytona-sensors.com/engine_tuning/Timing_Torque.gif

'MBT' is Maximum Brake Torque

Feeling a difference while driving is well nigh impossible to get to that last percentage point of power, although it will get onto the plateau on that curve. But the spark could still be 5 ck deg too advanced or too retarded from best. But we dont know what best is....for the full range of operating conditions.

 

Peter

 

Fig2.8 shows the top few percent of the MBT curves for different rpm ( N) and loads ( Pim, KPa).

http://liu.diva-portal.org/smash/get/diva2:23960/FULLTEXT01.pdf

The peakiest curve was for 1200rpm at 40kPa ( ie 0.4Bar, ie light load)

So thats where the TR engine will show the greatest diffferences in 'feel' with different spark advances, hence the region of the 123 settings to change for best part load running.

Edited by Peter Cobbold
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  • 2 weeks later...

 

Interesting video from TR member on tune 123 on a 6 cylinder car with a Kent TH6 camshaft.

 

12 mins in he shows his optimal settings.

 

Interesting that he has a higher advance at tickover to keep it smooth and (peter ?) I assume to maximise the efficiency of the burn at tickover.

This then drops off to what looks to be a normal curve, i assume to avoid pinking.

 

Snowy

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