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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
Posts: 2,826
My 930 factory manual seems to lack some significant graphs etc beyond 77, 78-79 US/CA models, although it often references RoW and Japan model numbers. Go figure..

However it says

(on page 28-14, titled "IGNITION SYSTEM 1978 MODEL"):

"California version cars are equipped with a distributor having a double vacuum unit.

At idle, the intake vacuum produces ignition retard, which is eliminated when the throttle is opened slightly.

Boost pressure is used for full throttle ignition retard control. This is to prevent excessive ignition advance at full throttle (initial ignition timing is 5 degrees earlier than U.S.A. version)"
So this appears to be smog-related for CA only, but the salient point is that early 3.3L California cars (a) have two nipples on the can and (b) use that second nipple for active boost retard. Assuming that not too much was lost in the translation from German.

The graph on page 28-4d entitled "Vacuum Retard/Advance Curve - Turbo Engine 1978 - California" shows different ignition curves either side of a "pressure" centerline, up to 300 mbar pressure on the left, and up to 400 mbar vacuum on the right.

(the graphs for the other models covered in my manual show only advance due to vacuum).

Now, whether the '80 up (RoW) or '86-up (US) distributors with two nipples behave like the '78 California distributor - or differently again - is a good question, and one I cannot reliably answer, as my manual doesn't provide graphs for those cars..
'77 S with '78 930 power and a few other things.
Old 09-11-2007, 03:49 PM
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