harlequin Posted July 3, 2020 Report Share Posted July 3, 2020 I have borrowed a Gunson gas tester from a friend to check my Stromberg carbs on my TR6 which was all ok, I noticed that it also checked dwell angle so just out of interest I checked it and was surprised to get a reading of 25°. My Haynes manual gives a figure of 35°+/-3° for a distributor with points The car is fitted with an Aldon Ignitor module instead of points, so to my question, is the low dwell angle normal for these modules? and if so does this mean that my coil is not becoming fully saturated/charged and I am possibly losing performance? George Quote Link to post Share on other sites
RobH Posted July 3, 2020 Report Share Posted July 3, 2020 (edited) There must be some tolerance and production variability in the position and strength of the hall magnets and in the sensitivity of the hall sensor but since the things are potted you can't tell by looking, and of course the makers never divulge the figures. However, that should just be a trigger and the dwell is probably set electronically inside the unit and is not adjustable of course. Even with the recommended dwell, there is insufficient time to fully 'charge' a coil at higher revs. If your dwell angle really is that much shorter, then the effect will be worse. That would certainly weaken the spark further relative to low/medium revs but whether that translates to any loss of power must depend on the particular characteristics of the engine. It is quite likely that there is still enough spark energy present to initiate proper combustion. The use of a high-output coil may compensate a bit by having more energy anyway, so that the greater drop is not noticeable. I think the definitive answer to your last question can only be provided by a rolling road test. If you are really interested, I found this excellent paper on ignition systems which covers the background well: http://tr4a.weebly.com/uploads/2/1/9/8/21980360/capacitive_discharge_ignition_vs_magnetic_discharge_ignition..pdf Edited July 3, 2020 by RobH Quote Link to post Share on other sites
harlequin Posted July 3, 2020 Author Report Share Posted July 3, 2020 Thanks for your reply Rob As you say the manufacturer seems shy about giving out figures which is a pity, the module is probably 10 years old so perhaps the magnets are fading or the sensor is weak so it would have been good to have a figure to check against. Meanwhile 2 thirds of the required dwell angle cannot be good so I shall investigate further. Thanks for the link to the ignition system wright up, I will attempt to go through it and hopefully take something onboard George Quote Link to post Share on other sites
stuart Posted July 4, 2020 Report Share Posted July 4, 2020 Yet another reason to stick with points Stuart. Quote Link to post Share on other sites
SpitFireSIX Posted July 4, 2020 Report Share Posted July 4, 2020 The dwell meter is for setting points. Results are meaningless on your semiconductor system. Curiosity killed the cat. Quote Link to post Share on other sites
harlequin Posted July 4, 2020 Author Report Share Posted July 4, 2020 (edited) 5 hours ago, SpitFireSIX said: The dwell meter is for setting points. Results are meaningless on your semiconductor system. Curiosity killed the cat. Agreed but the coil remains the same beast no matter what triggers it and will require the same amount of time to become saturated, this is why 8 cylinder engines often have dual points to increase the dwell angle from about 30° (due to the 8 lobe distributor cam) by using a bit of overlap. (I have been doing some reading ) I am going to check the dwell angle on a friends car that is pretty much the same as mine just to see if it's the same 25° As Stuart stated "there is a lot to be said for keeping things simple and using points" George Edited July 4, 2020 by harlequin Quote Link to post Share on other sites
Mike C Posted July 4, 2020 Report Share Posted July 4, 2020 1 hour ago, SpitFireSIX said: The dwell meter is for setting points. Results are meaningless on your semiconductor system. Curiosity killed the cat. I'd have a look at the switching speed and wave form of an electronic switching system if I wanted to compare it to cam operated points. I've had no problems with an Aldon, unfortunately it reliably fed sparks to the plugs until the tacho went off the dial one time I went to change with an unexpected throttle linkage jammed wide open. Quote Link to post Share on other sites
RobH Posted July 4, 2020 Report Share Posted July 4, 2020 Where this gets complicated is that with points both the 'on' and 'off' times vary in proportion so the reading remains constant(ish) over a rev range. Some of the 'cleverer' electronic systems give a fixed 'on' time at low revs in order to minimise coil heating. That means the ratio of on-to-off changes so the meter doesn't show the correct dwell - in fact the slower the revs the shorter the indicated dwell % will be. You can tell if this is happening if the reading changes with a change in revs. Quote Link to post Share on other sites
harlequin Posted July 4, 2020 Author Report Share Posted July 4, 2020 If the Aldon was one of the clever ones mine no longer is as it gives the same reading from 800 rpm to 2500 rpm George Quote Link to post Share on other sites
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