Lotus Elan

Which ignition coil for race engine?

PostPost by: Vali » Wed Mar 30, 2022 10:43 am

Which ignition coil do you racers use with the raceengins (rpm around 8000)?

TTR supplied me a 1 Ohm ignition coil without any branding for my car with conversed electronic ignition distributor.
https://www.tonythompsonracing.co.uk/parts/models/elan-s1/electronic-ignition-2007-ttr-spec-for-competition-all-steel-engines-over-150bhp/
I guess there should be a resistor wired between for it?

Or use a 3 Ohm ignition coil like I do on my road Elan S4?

Pertronix with the Flamethrower has a table sheet which says 4 cyl engines below 6000 rpm should use their 3 Ohm Flamethrower coil but for high rev 4cyl engines above 6000 rpm a 1.5 Ohm coil should be used ...
According to FIA I must use a 3 Ohm ignition coil but I´m afraid it won´t work well if the coil has no time to recharge at higher rpm? If I understand the FIA then systems like a MSD is not allowed, too.

FIA rules for Period F:
6.5.1
Cars of Period F with evidence of period use of electronic ignition may use a non-period electronic ignition system provided this system is triggered by contact breaker(s), utilises an ignition coil with a minimum resistance of 3 ohms, the spark is distributed by a rotor arm and the timing of the spark is controlled entirely by mechanical means.

Multi spark systems and systems where the timing of the spark is altered electronically are not permitted.Exceptionally, where evidence exists that alternative methods of triggering were legally used in period, this may be utilised provided the method is identical in every respect to the period method.



What are your experiences with ignition systems and how is it done on your racecars?

I would like to plan and fabricate my wiring harness for the car soon and before that I want to know what I will use for the ignition system.
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PostPost by: rgh0 » Wed Mar 30, 2022 7:51 pm

I use a points ignition and a Bosch 3 ohm coil with no problems to 8000+ rpm.

cheers
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PostPost by: batfish » Thu Mar 31, 2022 8:05 pm

Hi I have always used Lucas sports coil, either with points or Aldon Ignitor.
Andy
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PostPost by: mbell » Thu Mar 31, 2022 9:51 pm

I can't comment on the racing aspect. But my experience of coils on the road is that 3 ohms is fine, a 1.5ohm (with out ballast) will overheat after an hour or so. Now if running at high revs and short races, you might get away with the 1.5 ohm coil.

I'd probably size the wiring based on a 1 ohm coil (~12amps) to be safe but run a 3 ohm coil. Unless I had suitable test period to test reliability of a 1.5 ohm coil.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: 2cams70 » Fri Apr 01, 2022 2:03 am

Think of it this way. Provided you've got the fire started it doesn't really matter whether you've got it started using a matchstick or a huge blowtorch. The result is the same. The timing of the spark is far more important. That analogy could relate to a lot of things come to think of it!!
1970 Ford Escort Twin Cam
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PostPost by: Vali » Sat Apr 02, 2022 8:32 am

Thank you for your replys. :)
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PostPost by: Vali » Tue Apr 26, 2022 6:16 am

mbell wrote:I'd probably size the wiring based on a 1 ohm coil (~12amps) to be safe but run a 3 ohm coil. Unless I had suitable test period to test reliability of a 1.5 ohm coil.


So you would use a wire with 2.0mm² or bigger for it to the positive terminal of the coil.
If you look at Pertronix with the Flamethrower they recommend in their install instructions a 12 gauge wire which would be 4 mm² wires which might be overkill but helps to get more voltage to the coil (less voltage drop)

But what´s about the negative side? The 2 wires from the electronic ignition modules are all only 0.75mm² if I´m not wrong. Same goes for the wires of the rev limiter modules (like Omex or Lumenition rev limiter).

A 0.75mm² wire would not handle 12 amps from 1 ohm coil for a long time and get hot, too? :?

All the install instructions I can find only tells about removing the ballast resistor and get a 12 gauge wire into but never mentions the negative side ...
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PostPost by: Billmack » Tue Apr 26, 2022 7:07 am

Got to be something wrong with that 12 amo figure
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PostPost by: Andy8421 » Tue Apr 26, 2022 9:51 am

With due thanks to Georg Ohm:

I = V / R
= 12 volts / 1 ohm
= 12 amps

However, when the car is running you have to consider the duty cycle (on / off ratio) of the current down the wire, and also that the coil is an inductor and won't look anything like a 1 ohm load at the switching frequency of the points / ignition electronics.

Then again, with the engine stopped, if the points are closed, the coil will draw 12 amps (most electronic ignition systems will detect this condition and not power the coil if the engine is stopped). This can cook the coil, and I believe Lucas advised against leaving the ignition on in one of their technical publications.

..and when it comes to sizing wire, it is generally a combination of acceptable voltage drop and acceptable temperature rise. Acceptable voltage drop is a function of the circuit design parameters, and acceptable temp rise is usually driven by the temperature stability of the insulation.

So, in the best tradition of engineering, it all depends......
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PostPost by: Slowtus » Tue Apr 26, 2022 4:14 pm

With due thanks to City & Guilds

As for the wire, if you really want to go at it...R = ρl/A.
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PostPost by: mbell » Tue Apr 26, 2022 5:24 pm

Vali wrote:So you would use a wire with 2.0mm² or bigger for it to the positive terminal of the coil.


I haven't done the calculation to know what size I would use, I would use use a wire sized based on my worse case expected. The worse case you mentioned was 1ohm coil, so unless you rule that out I would sized based off that.

Vali wrote:The 2 wires from the electronic ignition modules are all only 0.75mm² if I´m not wrong.


What do the modules manual say about supported coils? I suspect those modules won't claim to support the switching current of a 1ohm coil. I know my 123dizzy specify minimal coil resistances (1.5ohm my memory).
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: Vali » Fri Apr 29, 2022 6:00 am

There is no manual for my system.
It´s from TTR/ H&H Ignition Solutions.

I got hold of H&H Ignition Solutions and they told me the coils are OE factory specification to ran it with original vehicle wiring of cars of that era.
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PostPost by: mbell » Fri Apr 29, 2022 5:56 pm

OE Spec would be 3ohm coil or 1.5 ohm coil + 1.5 ohm ballast.
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