Lotus Elan

Lucas distributor

PostPost by: SpeedModel » Sun Mar 18, 2018 3:38 am

The original 40953A 23D4 distributor on my Elan S1 was changed for a later Lucas 41471 E 43D4 by the prior owner. I would be grateful to learn the difference between these two distributors and how performance could be impacted by the change.
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PostPost by: nmauduit » Sun Mar 18, 2018 10:19 am

The main difference would theoretically lie in the timing curve as the later model was designed to match later engines

http://mgaguru.com/mgtech/ignition/pdf/ ... _specs.pdf

though in practice actual curve depends on the condition of the distributor innards, unless it is new or just checked/calibrated

http://mgaguru.com/mgtech/ignition/pdf/ ... s_dist.pdf

depending on level of tune you expect, the first step would be to check when advance starts increasing, when it reaches its maximum, and the static and max advance level. Once this setting optimal for your specific engine, if your are still not satisfied with the ignition curve, then the next step would be to start playing with the distributor mechanism, springs etc. or get it recurved from a known good place. Of course, ignition is only one part of a completely tuning an engine (everything being in good condition, it relies for instance on a good carburetion state of tune). Working with a rolling road or similar reliable reference may be required to fine tune to a level of detail difficult to feel otherwise.
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PostPost by: ricarbo » Sun Mar 18, 2018 4:24 pm

The 41471 is listed by several sources as being a replacement for the 41189, which was fitted to later engines. It has a different curve from the 40953.
According to Miles Wilkins book, the 40953 has a total advance of 24 degrees and the 41189 has a total of 14 degrees and the curves are different.
I don?t know how the different distributors would affect performance. Given that modern petrol is different, I would imagine neither distributor is ideal, even if it is unworn.
What I do know is that the 43D4 type is a different body from the 23D4 type and so all the parts are different. The 43D4 is slightly larger, with a longer rotor arm. They both have a contact breaker gap of 0.015?, plus or minus 0.001?. The dwell angles are different, 60 degrees (plus or minus 3) on the 23D4 and 51 (plus or minus 5) on the 43D4, meaning the coil has less time that it is connected to the battery. I don?t know if this has any implications, for example on which coil to use. What I would say is that my Sprint has a 41471, standard coil and optional electronic ignition and seems quite happy.
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PostPost by: SpeedModel » Mon Mar 19, 2018 2:47 am

Thank you for the insight gentlemen. This 41471 43D4 distributor is fitted with a 7 degree cam, less advance than anticipated. I will try to find a distributor shop in my area with a curve test machine and have it measured. Afterward I will update this thread with any new information gleaned.
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PostPost by: ricarbo » Mon Mar 19, 2018 8:04 am

I think the 7 degrees will be distributor degrees, therefore 14 crankshaft degrees, as the 41189.
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PostPost by: nmauduit » Mon Mar 19, 2018 8:48 am

ricarbo wrote:I think the 7 degrees will be distributor degrees, therefore 14 crankshaft degrees, as the 41189.


yes, so while waiting for a confirmation, checking the static setting to 14 or even 16 in case of a Weber head would lead to 28-30 total advance (to check with a strobe light, including when the max is reached), would let the car run decently while choosing the next step for a better tune if required.
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