Lotus Elan

Distributor / Ignition questions

PostPost by: seniorchristo » Sat Dec 31, 2016 10:07 pm

I have a 1967 Elan with a tall block conversion, Weber carbs, Sprint like cams and unknown compression ratio.

I found when checking my ignition timing the settings were 18 crankshaft degrees at 700 RPM with a maximum of 33 degrees at full advance. The distributor is a - 41225D with a vacuum retard capsule that is not hooked up. According to the Lotus manual this distributor should have a total advance of 14 crankshaft degrees which approximates my readings. Is this appropriate for my engine?

Also, the wiring from the coil and distributor go to an electrical box which I assume is electronic ignition. I thought electronic ignition eliminated the points and condenser but mine are intact. I am an electrical dummy but determined to learn enough to keep my Elan running reliably. Thanks :)
Chris
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PostPost by: rgh0 » Sun Jan 01, 2017 12:04 am

Hi Chris
The exact advance curve you need depends on details of the engine build and fuel being used so it really needs to be fine tuned on a dyno.

You current curve is not really the best for you current engine specification

A good starting point would be the 41189 D Cam / Big Valve curve or the 41225 European / Domestic non emissions Dellorto curve. These have around 10 - 12 degrees static up to about 1000 rpm and then a linear curve to around 25 to 29 degrees at around 5000 rpm.

The engines will generally tolerate a quicker advance than these curves so you can try setting it up with the maximum coming in around 4000 rpm which gives a better mid-range response and better cruising economy.

Your mysterious box is probably either an electronic rev limiter or a transistorised ignition unit that is triggered by the standard points.

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PostPost by: seniorchristo » Sun Jan 01, 2017 3:34 am

Rohan
I seem to remember reaching maximum advance around 3000 rpm which could indicate worn springs. Can I expect better performance if the curve is extended to 4000 as you suggest? I am planning on having the distributor rebuilt but I won't have the option of a dyno or even trial and error testing. The shop I plan on using (Advanced Distributors) has an excellent reputation with British Cars and they curve the dizzy based on basic engine parameters. Thanks
Chris :)
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PostPost by: rgh0 » Sun Jan 01, 2017 4:15 am

33 degrees total advance at 3000 rpm should have your engine knocking heavily, 18 degrees advance at 700 rpm is to much. Potentially the dizzy you have was recurved at some stage because 12 degrees static to 1000 rpm timing plus 15 degrees of mechanical advance above that is not far of what you would want. 3000 rpm is a little early for full advance though, i would aim for it to be full advance at 4000 rpm.


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PostPost by: Allison » Mon Jan 02, 2017 10:33 am

Hi Chris,
your electrical box could be a Boyer Bransden unit. I use these to prolong the life of the points - and they are excellent! The idea is that you still use the points (and possibly condenser) to trigger the ignition but only with a fraction of the electrical current. The Boyer Bransden unit is where the main part of the current flows.
On one Elan, the life of the points is extended from about 1,500/2,000 miles to around 20,000 so you have a lot more reliability on the road. All cars seem to be different but if yours was a "points eater" then this might explain why you have a points based "box of tricks"
Best wishes
Peter
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PostPost by: seniorchristo » Mon Jan 02, 2017 12:59 pm

Peter
Here is a picture of the box. There are 6 wires coming out including those from the coil and distributor.
Thanks, Chris :)
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PostPost by: billwill » Tue Jan 03, 2017 12:55 am

Allison wrote:Hi Chris,
your electrical box could be a Boyer Bransden unit. I use these to prolong the life of the points - and they are excellent! The idea is that you still use the points (and possibly condenser) to trigger the ignition but only with a fraction of the electrical current. The Boyer Bransden unit is where the main part of the current flows.
On one Elan, the life of the points is extended from about 1,500/2,000 miles to around 20,000 so you have a lot more reliability on the road. All cars seem to be different but if yours was a "points eater" then this might explain why you have a points based "box of tricks"
Best wishes
Peter



I use a Maplin kit system to do the same as the unit you describe. It reduces the current through the points to a max of 1 amp, while 'amplifying' that amp to whatever the coil really needs.

I increased the wattage rating of the resistors that limit the current to 1 amp, because the original Maplin (Vellerman ?) design has resistors with way insufficient power rating. If you stopped the engine in a position that the points were closed and ignition was turned on they would surely have burned out.
Bill Williams

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