Hi Robert,
It is generally reckoned that the earlier distributors gave better
performance as they weren't concerned with emissions, but there were 24 (at
my count) different distributors used over the years! You would have to
chose based first on high or low compression, then on other factors of the
engine design, or you could end up with a worse curve than the original.
Even then the very crude mechanical design probably meant that the original
curve was only an approximation to the ideal, and since then used engines
and distributors have much wear, parts replacements possibly not to original
spec, different fuel grades etc. any one distributor will probably give
different results on different engines and no two distributors of the same
serial number are now the same! Original springs are not available, one has
to find someone with a distributor testing machine and a supply of springs
for tweaking and trial and error - which only gets to back to the original
approximation anyway, and despite all the curves and recommended dynamic
settings the only rear setting for any particular installation is to have it
as advanced as possible but not pinking on any combination of throttle, revs
and load.
What I would love to investigate is a system using a knock sensor which
would continually advance and retard the ignition giving an ideal setting
for every possible combination of engine, fuel, revs, throttle opening etc.
If you want to go to points you are probably best off with a new 'Eurospec'
unit which will be of a known curve, and as Europe was less fussed about
emissions than North America in the early days probably give better
performance.
Personally, if I had a working Opus I would use it purely for its rarity
value, but carry something else as a spare! Next choice for originality
would be the 45DM4 with CEI (the CEI units are still available)which seems
to have been interchangeable with the Opus. After that my choice would be a
45D4 European unit with points - the 45D4 is slightly smaller than the 25D4
and is easier to adjust and remove complete with its clamp plate, the loss
of the vernier adjustment of timing is neither here nor there. But with all
these you are back to the 'advance it till it pinks then back it off till it
stops' method of setting. I would not use an aftermarket electronic unit or
you are back to carrying points as a spare for when they fail.
Thanks for that site link. Interesting, if a little tedious to navigate.
PaulH.
----- Original Message -----
From: "Robert Guinness" <rjglaw@swbell.net>
To: "MG listserv" <mgs@autox.team.net>
Sent: Tuesday, October 21, 2003 7:48 PM
Subject: Re: Factory Distributor Swap
> ... I am trying to decide
> whether I should go "original original" with an Opus, go "later
> original" with the CEI swap, or just use the 25D that the PO installed.
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