Doug,
Look in the Comp Manual for total advance.
I used to run 33-35 degrees in a race-prepped 1147,
but since the combustion chamber is different in a
1296, it depends.
If you have access to a chassis dyno, that's the best
way to find out.
But you can sneak up on it a degree at a time.
Good luck,
Carter Shore
--- Douglas Braun & Nadia Papakonstantinou
<dougnad@bellatlantic.net> wrote:
>
> Hello,
>
> Last weekend I finished messing with my engine (1972
> late MK IV, 8:1 compression).
> I installed the "fast road" cam that SpitBits sells
> (with new lifters), and I had about .090" milled
> off my head, which gives me a compression of about
> 9.25:1, as far as I can tell.
>
> These changes make the engine more or less like the
> non-emission 1300 engines.
>
> The car already had twin HS2s and a Pacesetter
> header
> installed (with stock exhaust).
>
> It definitely has more "zing" now. The 1972 was
> originally
> the wimpiest model year. In stock form, the car did
> 0-60
> in about 15.5. Now, after the cam is broken in, I
> could probably do it in about 11.5 seconds.
>
> It runs well, and still does not knock on regular
> 87-octane gas.
>
>
> My one question is: What is the optimum timing? I
> do
> not mean the idle value but the actual advance in
> the power
> band (say 4000 RPM) at full throttle. (I have no
> vacuum connection
> to my distributor, since it is the "retard" style
> and there is
> no way to connect that to the HS2s).
>
> After looking at all the tables of data for the
> various MK III and
> MK IV distributors in my Bentley book, it looks like
> the
> non-emission cars actually had about 27-28 degrees
> advance
> at 4000 RPM. But it is hard to say for sure since
> the different
> distributors all had different vacuum units.
>
> One bit of trivia: All of the distributors I had
> data for
> (five of them) have about the same shape advance
> curve above 1500 RPM.
> The change in advance from 1500 to 5000 RPM ranges
> from 10 to 12 degrees.
> The only major difference is the amount of advance
> from 0 to 1500 RPM,
> which ranges from 10 to 20 degrees. The models with
> the large amount
> of low-RPM advance are supposed to have retarded
> idle timing to
> compensate.
>
> Doug Braun
> '72 Spit
>
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