Advance curve for 23D4 41189A distributor

[RotoFlexible]

I have seen some discussions of advance curves in the past, but unfortunately the search function isn't working for me this morning. My apologies if this has been covered.
I've found someone who will morph my 40953 distributor into a 41189A (for a Weber Sprint conversion) as well as rebuild it. Of my Four Pillars of Wisdom (Wilkins, Buckland, Bean, and the 1966-vintage Elan shop manual), only Wilkins has anything to say about advance curves. Unfortunately, his numbers don't match up to those my distributor man has for the 41189A (presumably from Lucas). The numbers below are advance at the distributor, i.e., RPM and advance are half of that at the crankshaft, with no static advance added):

Lucas figures
RPM ........... Distributor Advance (degrees)
400 ........... 0
600 ........... 1
1000 ........... 5
3200 ........... 7

Wilkins figures (normalized to dist. rpm and advance)
RPM ........... Advance
<1000 ........... 0
1250 ........... 1.25 (2.5 crankshaft)
1500 ........... 2.25 (4.5 ")
1750 ........... 3.5 (7.0 ")
2000 ........... 4.65 (9.3 ")
2250 ........... 5.75 (11.5 ")
2500+ ........... 7.0 (max. advance) (14 crankshaft)

Wilkins shows a curve to match these figures. This means no advance under 2000 (crankshaft) RPM and full advance at 5000 RPM. The factory curve, by contrast, is very steep from idle to 2000 (crankshaft), then quite flat from there to max advance at 6400 (crankshaft).
He will set it up any way I want. Any opinions or additional data? The later workshop manuals may have something, but Wilkins notes that "in the manuals, Lotus get confused between crankshaft rpm and distributor rpm; in some cases, static settings have been added, in others they have not!"
Thanks in advance for any insight.

[stuartgb100]

Andrew,

I started a thread back in the autumn of '05 that received a deal of opinion (though as I recall, not conclusive). The Search function is not working for me, either, so I cannot be more specific.

However, in the meantime this may be of interest:

Lucas put me in touch with H&H Ignition Solutions here in the UK. After about 2 months of to and fro-ing, phonecalls to Paul Matty. QED, etc, we finally settled on H&H's standard spec for this distributor.

This spec was based on a batch of unused 41189D distributors that they had inherited and subsequently analysed, and also backed up by a wad of Lucas distributor data from the '70s that I sent them (they had not seen this data before).

My distributor settings as follows:

No advance below 400 rpm

600 dizzy rpm Lucas 0 - 2 degrees, H&H 1 degree
1000 dizzy rpm Lucas 4 - 6 degrees, H&H 4.5 degrees
3250 dizzy rpm Lucas 6 - 8 degrees, H&H 8 degrees

This is dizzy rpm (so x2 for crank rpm) and is in addition to the 12 degree static setting (so a maximum of 28 degrees advance at 6500 crank rpm) and is on a standard twink (points, cams etc).

I fully expected this to be a bit of a compromise, and that more research etc would be needed. However, I've had so much fun driving a really free-revving and willing engine that in the last 12 months I haven't thought about it. Your post has resurrected the topic.

In the meantime, whilst the Search function seems temperamental, here's a couple of links to explore:

http://www.jcna.com/library/tech/tech0015.html

(a Google on Marcel Chichak will give more results)

http://www.teglerizer.com/mgstuff/advance_curves.htm

HTH.

Regards,
Stuart.

[types26/36]

I started a thread back in the autumn of '05 that received a deal of opinion (though as I recall, not conclusive). The Search function is not working for me, either, so I cannot be more specific..

Stuart,
Even although the search might not work there are ways of getting round it
I think these are the threads you started
http://www.lotuselan.net/forums/viewtop ... ght=#10136
http://www.lotuselan.net/forums/viewtop ... ght=#10120

[bcmc33]

For information - I posted a question regarding the search not working, and was advised to put key words in double quotes ("......"). This now works every time.


Brian Clarke

[RotoFlexible]

Thanks Stuart et al., those are exactly the pointers I need. I'll check out these various resources and come up with some numbers. I did find an excellent article by Marcel Chichak on tuning Lucas distributors, the how and some of the why. It is amazing how much you learn doing one of these projects.
Edit: The article by Marcel Chichak is the same as Stuart cited in his post. I found it on a US Triumph owner's site.

[RotoFlexible]

OK, we now have three data points. Time to get out the graph paper. As the attached diagram shows, the Lucas and H&H/sgbooth curves are very close, and quite different from the Wilkins curve. The mystery is why the Wilkins data is so different from both the Lucas and H&H numbers.
Stuart, I believe from previous posts that you have a Sprint, so when you write "a standard twink (points, cams etc)" does that mean a standard Sprint twink? With Webers/Dellortos? The static advance you are running suggests this is the case. If so, then we have a real-world example of someone who is happy with near-Lucas settings (and more importantly, is not experiencing pinking or detonation at low revs.) That argues in favor of using either the Lucas or H&H numbers and ignoring Wilkins on this matter.

[stuartgb100]

Andrew,

Yes a standard Sprint with webers (AFAIK). However, the 41189 distributor was not limited to just the Sprint, but also the SE using the C type cam and webers. Only the static timing changed. I am not aware that the advance characteristics were modified for the Sprint.

If I'm correct, then the Lucas/H&H settings would be specific to the 41189 distributor, irrespective of which model it is fitted to.

Regards,
Stuart.

[Garibaldi]

OK, we now have three data points. Time to get out the graph paper. As the attached diagram shows, the Lucas and H&H/sgbooth curves are very close, and quite different from the Wilkins curve.

-----------------SNIP---------------------

The mystery is why the Wilkins data is so different from both the Lucas and H&H numbers. That argues in favor of using either the Lucas or H&H numbers and ignoring Wilkins on this matter.

<<<<<IGNORANCEALERT>>>>>>>>>>>
IRT ignoring Wilkins' distributor advance: is it possible that these are figures that he obtained through iteration to find the optimum curve? Secondly, has anyone had their Twink "dyno-tuned [US]" or "tuned on a rolling road [UK]?" During the time of the mechanical/vaccum advance distributor, changing advance to optimize for individual engines was possible/if not commonplace.

GP

[ppnelan]

Andrew,

Why don't you sell your 40953, as it is a NLA item just for Stromberg (the best torque!) Twin Cams, and buy a new/recon 41189 ?
After all, they are easy enough to get hold of, in the UK at least.
You may even make some money on the deal...

Matthew

[RotoFlexible]

Andrew,

Why don't you sell your 40953, as it is a NLA item just for Stromberg (the best torque!) Twin Cams, and buy a new/recon 41189 ?
After all, they are easy enough to get hold of, in the UK at least.
You may even make some money on the deal...

Matthew

Actually, there is a NOS 23D4 41189A on ebay (UK) right now. I'll be interested to see what it will go for. However, this gentleman in Ohio will rebuild my distributor to as- or better-than-new condition and appearance, recurve it to my spec or Lucas spec, and document before-and-after performance for about $75. Hard to beat that, and I know exactly what I'm getting. But you make a good point...

[Garibaldi]

-----------SNIP-------
However, this gentleman in Ohio will rebuild my distributor to as- or better-than-new condition and appearance, recurve it to my spec or Lucas spec, and document before-and-after performance for about $75

----------SNIP--------

This is a resource that I hope you can share with the list.
GP

[steveww]

http://www.123ignition.nl/ are working on a version for the Ford/Lotus engine. Marcel is doing the development work on his Lotus Cortina, it should be available in time for the summer.

[iain.hamlton]

Andrew, All.

There has been lots said about this in the past....

http://www.lotuselan.net/forums/viewtop ... highlight=

I went so far as to measure my distributor. After doing so, I find it best to set up the maximum value (over 2500 rpm) and work back to the static.

best regards, iain

[RotoFlexible]

Andrew, All.

There has been lots said about this in the past....

http://www.lotuselan.net/forums/viewtop ... highlight=

best regards, iain

That's the topic I was looking for! Thanks. It seems that the bottom line is that the Lucas numbers for the 41189A will work fine.

This is a resource that I hope you can share with the list.

Certainly, although I must emphasize that I haven't actually seen his work yet. I've seen some recommendations on the web and had a very encouraging email exchange with him. His name is Robert Sarama, and you can reach him at [email protected].
Maybe we should have a forum to list resources that members have found. I am looking for a Weber carb reconditioner in the U.S., for example. Pierce Manifolds in Calif. is the only one I've found so far.