Re: Ignition timing question

["Jeff M" <tystorm@email.msn.com>]

Me thinks the reduced timing/not in boost of your Sy is from the dizzy air
mix caused by the Vortec swirl heads, fast burn they are so, less timing?
These heads are great for low rpm VE numbers, big torque for little V6 but a
bit restrictive at higher air velocities/rpms.  My Ty motor does not have
the swirl port configuration anymore and my timing is advanced more as
compared to stock (also because my compression ratio has dropped too), so
this may confirm it.

Jeff M


> I was going through some of my *old* engine stuff & came on some
> distributor curves once set on a '65 SBC.
>
> The timing was around 15° static, centrifugal max about 25°, starting @
> 1000 (engine) RPM, maxed @ 3000 RPM (total = 40°).  Vacuum advance would
> add another 12° or so at low engine loads.
>
> Studied some timing specs for various Syclone (7749 ECU) chips just now -
> *radical* differences!  Overall timing looks to be about *half* what the
> old dizzy specs were.
>
> Assume the normally aspirated section of the Advance vs. MAP & RPM table,
> i.e., ignore values above 1 bar.  Timing maxed at 3200 RPMs at about
> 16-17°; around 20° max added for light load conditions.  Naturally, retard
> needed under boost, but the NA part of the table is real different from
> what I'd expect.
>
> Seems to me *lots* of timing could be added at cruise & light load (light
> for a turbo) conditions - am I missing something here?  Are these big
> differences for emissions reasons?
>
> Thanks for any clarification -
>
> Puzzled - Barry - Sy#26
>
> Timing looks to be about half what the old distributor curves were
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