Lotus Elan

Electronic ignition thoughts

PostPost by: vernon.taylor » Fri Aug 10, 2012 12:53 pm

Salut

Something started me off on thinking about electronic ignition: to limit any responses (which I would gratefully accept) I mean assisted points (or magnetic replacement) electronic ignition. What I've managed to understand so far:

1. Transistor assisted ignition: usually a two-stage transistor amplifier before the coil, resulting in a higher voltage spark, and reduced contact wear.

2. Inductive discharge EI - for example: http://www.boyerbransden.com/IDunits.html. I can't think what this might be - maybe just a controlled (dwell/advance?) version of the above.

3. Capacitive discharge EI - voltage controlled through energy storage in a capacitor. High speed switching transistors used for a fast and high voltage spark.

I'll probably start by experimenting with 1) - should have suitable transistors and bits in a junk box. However I came across a multi-spark capacitor discharge circuit published in Silicon Chips a few years back:

http://www.molla.org/DIY-CDI/SC-DIY-CDI ... -hires.pdf

- it appears similar in operation to the MSD units except that multi-spark operation can be had up to 15,000 revs.

So to my question: is multi-spark electronic ignition a good idea for a road TC (dwell and advance controlled by the distributor) ?

Merci

Vernon
User avatar
vernon.taylor
Fourth Gear
Fourth Gear
 
Posts: 927
Joined: 05 Nov 2010
Location: Vaugneray, France

PostPost by: ricarbo » Fri Aug 10, 2012 4:09 pm

Many years ago i built up a circuit published in Practical Electronics for a capacitive discharge circuit which was quite fun (had to wind my own toroidal transformer, etc). Fitted it to my Triumph TR4 and never had to use the choke again - Strombergs - for a cold start. I coldn't detect any other difference in running. It did make quite a whine, though. Later I built several other kits, some of which failed and the one I have on the Elan is by Electronize Design (now defunct, i think). that incorporates a changeover switch to revert to normal operation in the event the electronics fail, but they never have. A capacitive type, it dumps 600 volts into the standard coil, via a thyristor. Difference is a stronger spark, visibly so on a plug run in free air. Disadvantage is it wouldn't run a rev counter of the RV1 current operated type, so I changed to a voltage operated rev counter. The points no longer wear electrically, but the manual says to put a drop of oil on the distributor shaft periodically and a smear of vaseline on the heel of the points (or oil on the felt pad), so there is still maintenance to be done, but much easier.
I'm pretty sure that just adding a transistor switch to the points will not improve the spark, just avoid the deterioration due to wear and consequent shift in timing. I think there is no difference between 'transistor assisted' and 'inductive'. The standard set up with points is inductive. I still have a copy of the Which report from July 1979 which tested 20 aftermarket systems including the Lucas electronic distributor (magnetic switching, inductive output). Their conclusion was that none of the electronic sytems gave a statistically provable benefit in acceleration performance or fuel consumption or presented an overwhelming case for change. Some gave better cold starting, but some, both capacitive and inductive types, were worse than the standard points set up, if well maintained. Some, but not all, would not work at all if the battery voltage was less than 8 volts, others 5 volts. Some, but not all, gave better running at over 6,000 rpm, when the coil ouput voltage of the standard set up started to drop a bit, but not enough to stop the plugs firing properly. I can email you a copy if you like, but it is from 1979. They also commented that the breakdown voltage of the distributor they were using was around 32 kv. Presumably not a good idea to exceed this.
With electronic ignition the advance remains under the control of the distributor, but the dwell may, or may not, be under the control of the electronics, depending on the design. I do not know if mutispark systems are an improvement, but can see they could clean up incomplete combustion, if that exists as a problem (doubt that it does).

Personally, I like not having to change the points and just check them with a dwell meter to see if the gap has altered, but i do keep up with the other maintance tasks.
Richard
ricarbo
Third Gear
Third Gear
 
Posts: 271
Joined: 14 Apr 2010
Location: Hove, East Sussex, England

PostPost by: vernon.taylor » Fri Aug 10, 2012 8:08 pm

Salut Richard

Thanks for the reply - if you have time to email me a copy of the comparison it could be interesting.

The transistor assisted EI also bump up the primary coil voltage as well as reducing current through the points.

The multi-spark circuit I linked addresses some of the points you mentioned - PCM frequency is over 20kHz, so not audible (older circuits used a 2kHz frequency). The switched capacitor discharge is from a generated and stabilised power supply that works from 5V up.

So the question still remains if a multi-spark system has advantages. It is said that a longer duration spark is an advantage (inductive systems), so I suppose multiple short sparks (same voltage) serve the same purpose? Though as you said, once the fire is lit do you need to keep holding the match or strike another?

I'll have to do some more reading.

@+

Vernon
User avatar
vernon.taylor
Fourth Gear
Fourth Gear
 
Posts: 927
Joined: 05 Nov 2010
Location: Vaugneray, France

PostPost by: ricarbo » Sat Aug 11, 2012 10:10 am

Will do Vernon, hopefully later today. I think that if I didn't have the set up I have, with which I am very happy, I would at least consider the Pertronix kit as it fits inside the distributor and can use the standard coil. it seems quite pricy, though at about ?140. I've never used or even seen one, but comments on other car sites seem favourable. Maybe someone else here has some useful advice?
all the best.
Richard
ricarbo
Third Gear
Third Gear
 
Posts: 271
Joined: 14 Apr 2010
Location: Hove, East Sussex, England

PostPost by: msd1107 » Sat Aug 11, 2012 4:24 pm

One of the advantages of high voltage and/or extended spark duration is more reliable ignition under adverse conditions - i.e. lean AFR.

Fuel economy continues to improve as the AFR becomes leaner. However, the twinc is notoriously resistant to lean conditions. Having a higher voltage and/or extended spark ignition helps this.

So Stromberg users can adjust their needles leaner and still retain acceptable running conditions with improved fuel economy.

Weber users can experiment with leaner idle jets and leaner off idle transition. Keith Frank has done a lot of work to provide constant AFRs to get rid of lean transition spots. Improved ignition should allow the user to select one or two steps leaner and still get acceptable running and throttle response.

David
1968 36/7988
User avatar
msd1107
Fourth Gear
Fourth Gear
 
Posts: 854
Joined: 24 Sep 2003
Location: Hollywood, CA USA

PostPost by: Rob_LaMoreaux » Sat Aug 11, 2012 7:13 pm

Multispark can be usefull, but most wear out the spark plugs too quick to be useful.

The petronix II or an external system that just uses the distributor for trigger then fires a higher energy coil are optimal for a TwinCam. Unfortunately the Ignitor II doesn't fit in the stock distributor last I checked so you end up having to buy the Petronix distributor which also gets rid of the scatter caused by wear in the distributor bushings.

The Ignitor I does not drive higher energy coils, but it does have the advantage of no points to wear out. The Ignitor II (and Petrronix distributor) drives higher energy coils and has adaptive dwell and engine stop cut off.

One of the best solutions has been developed by my coworkers and is headed for production vehicles, but probably won't be available aftermarket for a while. This is called Dual Coil Offset. It uses two coils per plug and fires them very quickly alternating between the two so you only have one high voltage start event. That way the energy is pumped into the gap opfr a long time withou the plug contact wear that multispark produces. A good description is at: http://youtu.be/nZ9elulEcig

I've got an Ignitor I but would love to get the Petronix distributor when the budget permits, unless I convert to EFI using stuff I am working on for work or the MSQuorivva.

Rob LaMoreaux
Rob_LaMoreaux
Third Gear
Third Gear
 
Posts: 372
Joined: 22 Sep 2003

PostPost by: msd1107 » Sat Aug 11, 2012 7:41 pm

High EGR systems have been used/proposed ever since emissions regulations came into effect. There is a lot of published data on this. However, our twincs are not suited for EGR. The first is that there is no provision for EGR. The second is that EGR requires a more robust, extended spark event due to the marginal combustion conditions existing in the highly diluted mixture.

Extended duration or multi spark systems may wear out a conventional spark plug more rapidly. There was a discussion recently on which spark plug to use in the twinc, with the conclusion being that the newer high mileage sparking plugs are over kill for the conventional ignition. However, their greater reliability is good to withstand the increased erosion due to the extended ignition event, so spark plug life would not be of such a concern.

David
1968 36/7988
User avatar
msd1107
Fourth Gear
Fourth Gear
 
Posts: 854
Joined: 24 Sep 2003
Location: Hollywood, CA USA

PostPost by: fatboyoz » Sun Aug 12, 2012 3:48 am

Rob,
The 2012 Pertronix catalogue is showing an Ignitor II for the twin cam 23D4 distributor. Part number 9LU-148.
http://www.pertronix.com/catalogs/pdf/p ... n_conv.pdf
Regards,
Colin.

Rob_LaMoreaux wrote:Multispark can be usefull, but most wear out the spark plugs too quick to be useful.

The petronix II or an external system that just uses the distributor for trigger then fires a higher energy coil are optimal for a TwinCam. Unfortunately the Ignitor II doesn't fit in the stock distributor last I checked so you end up having to buy the Petronix distributor which also gets rid of the scatter caused by wear in the distributor bushings.

The Ignitor I does not drive higher energy coils, but it does have the advantage of no points to wear out. The Ignitor II (and Petrronix distributor) drives higher energy coils and has adaptive dwell and engine stop cut off.

One of the best solutions has been developed by my coworkers and is headed for production vehicles, but probably won't be available aftermarket for a while. This is called Dual Coil Offset. It uses two coils per plug and fires them very quickly alternating between the two so you only have one high voltage start event. That way the energy is pumped into the gap opfr a long time withou the plug contact wear that multispark produces. A good description is at: http://youtu.be/nZ9elulEcig

I've got an Ignitor I but would love to get the Petronix distributor when the budget permits, unless I convert to EFI using stuff I am working on for work or the MSQuorivva.

Rob LaMoreaux
'68 S4 DHC
fatboyoz
Fourth Gear
Fourth Gear
 
Posts: 596
Joined: 04 Oct 2003
Location: Gold Coast QLD Australia

PostPost by: simonknee » Sat Aug 18, 2012 7:28 pm

I've got the Petronix II and it works well, plus looks the part in you cannot see it.
The car definitely feels "snappier" with it fitted.

I already had a 45D based distributor unit, this and the Pertronix were supplied buy Aldon.
Aldon were very helpful as the first Pertronix unit sent didn't fit the base plate in my dizzy.
Also they supplied a fresh one, no quibbles, when it died earlier this year.

The death of the unit coincided with having to jump start the car.
Shouldn't cause an issue but there you go.
Simon
'67 S3 FHC 36/7002
'69 +2 50/1370 (stolen '00)
User avatar
simonknee
Fourth Gear
Fourth Gear
 
Posts: 916
Joined: 18 Sep 2003
Location: London

PostPost by: elansprint » Tue Aug 21, 2012 8:01 am

Vernon nice site about the CDI i had a Sparkrite system on my old +2 30 years ago & it certainly made starting easier & ran strongly i might knock one of them up & try it seems to address all the old problems of low battery starting etc.
Ian
elansprint
Fourth Gear
Fourth Gear
 
Posts: 500
Joined: 12 Sep 2003

Total Online:

Users browsing this forum: No registered users and 13 guests