littlejim Posted July 1, 2017 Report Share Posted July 1, 2017 The other aspect that appeals Pete, is that with nothing to wear out, the timing remains perfect. With the points the rotor arm is wearing away as soon as you set things up and the timing is gradually changing. Whether you notice a difference is another matter, but when you are young it all sounds so important. Quote Link to post Share on other sites
Peter Cobbold Posted July 1, 2017 Report Share Posted July 1, 2017 The other aspect that appeals Pete, is that with nothing to wear out, the timing remains perfect. With the points the rotor arm is wearing away as soon as you set things up and the timing is gradually changing. Whether you notice a difference is another matter, but when you are young it all sounds so important. 5 crank degrees out either way makes about 1% fall in power http://prntscr.com/fqd1c7 Yes, I'm too old to obsess about that. Peter Quote Link to post Share on other sites
Ian Vincent Posted July 19, 2017 Report Share Posted July 19, 2017 Encouraged by the various comments above I took the plunge and fitted a Pertronix Ignitor to my TR3a earlier today. When I removed the points they were fairly pitted but nonetheless, the engine is noticeably smoother and started instantly. I have seen various comments on other Forums (Fora?) to the effect that to get maximum benefit from a Pertronix system (and assuming you have a high output coil) you need to increase the spark plug gap by about 10 thou. Does anyone on this forum have any experience of this - is it correct? And if so, what's the science behind it? Rgds Ian Quote Link to post Share on other sites
RogerH Posted July 19, 2017 Report Share Posted July 19, 2017 Hi Ian, the voltage produced by the coil is not an instantaneous 50Kv - it builds up. A smaller gap will allow an arc at a lower KV - eg 30KV So a bigger gap will only be bridged by a higher KV - eg 50KV. You don;t get something for nothing. The 50KV will take longer to generate so this may limit the revs or the revs may limit the KV The coil may run hotter at the higher level I think that's how it works. Why not try it and see. Roger Quote Link to post Share on other sites
AndyR100 Posted July 19, 2017 Report Share Posted July 19, 2017 I have seen various comments on other Forums (Fora?) to the effect that to get maximum benefit from a Pertronix system (and assuming you have a high output coil) you need to increase the spark plug gap by about 10 thou. Does anyone on this forum have any experience of this - is it correct? And if so, what's the science behind it? Rgds Ian On previous Triumphs (Herald, Spitfire, Stag) when switching to Pertronix I have opened up the plug gaps, I have been as wide as 35 thou, but settled on 30. The idea is that, assuming everything in your HT side is in good order, you'll get a bigger (wider/fatter) spark and the opportunity for a more complete burn. The flip-side is that the extra energy required to jump the gap may place extra load on some duff components in your HT side. I've never had a problem but others may have a different perspective. ....... Andy Quote Link to post Share on other sites
RobH Posted July 19, 2017 Report Share Posted July 19, 2017 Roger -you are correct that the gap determines the breakdown voltage but that has no real bearing on the heat. Heating comes during the 'dwell' period when the points (or semiconductor switch) are closed and the magnetic circuit has saturated. The only thing then limiting the current flow through the coil primary is the DC resistance of the winding and it is the "I squared R" loss from this which gives most of the heating of the coil. There is little extra heating during the discharge when the points open, as the circuit is then just discharging the stored magnetic energy. The voltage rise is pretty quick - the extra delay in reaching 50kV as opposed to 30kV is negligible. The risetime could be as fast as nanoseconds depending on the coil and other circuit characteristics, and revs do not affect it. What does happen with revs is that the dwell time gets shorter the faster the engine speed, so if the dwell is set to give full magnetic saturation at maximum revs, the coil will be baking for a lot longer at low revs (unless you have a more complicated electronic system which compensates.) So counter-intuitively the coil will be getting more electrical heating the slower you drive. The energy available for the spark from a given coil is fixed so if the spark voltage is higher, the duration must be shorter as the area under the curve must remain the same - so you might not gain anything by just widening the gap on a standard coil. To increase the spark energy will require a coil which has higher magnetic flux at saturation which I guess is how the Flamethrower and similar high output coils are designed. As Andy says, using a wider gap will increase the electrical stress on all the HT insulation including that of the coil. Quote Link to post Share on other sites
ianhoward Posted July 19, 2017 Report Share Posted July 19, 2017 Regarding plug gap, I also heard/read the recommendation of increasing the gap - I too have used 30 thou for a long time. As for the coil, I purchased the 'matching' Flamethrower coil at the same time as the ignition module (around 9-10 years ago if I remember correctly), however, this failed on me yesterday, so now have a Bosch 3 Ohm equivalent. It now seems better than it's been! Happy days! Cheers Ian Quote Link to post Share on other sites
Chris59 Posted July 20, 2017 Report Share Posted July 20, 2017 (edited) When I met Martin (DD) last week, his recommandation about the Flame Thrower coil was to increase the sparkplugs gap to .30 (about 1 mm), to help the coil to run less hot. Edited July 20, 2017 by Chris59 Quote Link to post Share on other sites
Ian Vincent Posted July 20, 2017 Report Share Posted July 20, 2017 Thanks all, query answered in a most comprehensive fashion. Rgds Ian PS This forum is brilliant for this sort of stuff. Quote Link to post Share on other sites
RogerH Posted July 20, 2017 Report Share Posted July 20, 2017 Hi Rob, thanks for that very comprehensive explanation. I knew when I was typing that the hole beneath me was getting bigger. Chris, 1mm = 0.040" 0.75mm = 0.030" Roger Quote Link to post Share on other sites
ianc Posted July 20, 2017 Report Share Posted July 20, 2017 On my modified TR4, with Piranha/Newtronic electronic ignition system and Lucas Sport coil, I have been using 32 thou gap on BP7HS plugs, as recommended by Neil Revington, since 1993. Ian Cornish Quote Link to post Share on other sites
Ian Vincent Posted July 20, 2017 Report Share Posted July 20, 2017 Which brings my next question: what is the difference between the BP6HS plugs that I am using and the BP7HS referred to by Ian Cornish? Rgds Ian Quote Link to post Share on other sites
Lebro Posted July 20, 2017 Report Share Posted July 20, 2017 The BP7HS is a hotter plug, ie is less likely to become fouled, the down side is, being hotter it could cause running on. Bob. Quote Link to post Share on other sites
RobH Posted July 20, 2017 Report Share Posted July 20, 2017 Not with NGK Bob - the 7 is cooler than the 6. Quote Link to post Share on other sites
Peter Cobbold Posted July 20, 2017 Report Share Posted July 20, 2017 The ups and downs of plug heat grades:https://www.boschsparkplugs.net/learning-center/article/225/heat-range-conversion-chart Peter Quote Link to post Share on other sites
Lebro Posted July 21, 2017 Report Share Posted July 21, 2017 Not with NGK Bob - the 7 is cooler than the 6. Of course, you are most correct !. Bob. Quote Link to post Share on other sites
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