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tirwin tirwin is offline
Hey, nice marmot.
 
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Join Date: Feb 2011
Location: Marietta, GA
Posts: 5,158
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Quote:
Originally Posted by 7783911 View Post
Ok, I am dense.....my 83 sc has two vacuum ports on the dizzy..the outer one is Advance? and is connected. The "inner" one (toward alternator) is retard?? and is currently disconnected and capped off. My original question was should i be putting that line back on and if so, what adjustments need to be made as a result.

Thanks...
Yes, the one towards the fan/alternator is retard. The other is advance.

The short answer is no, don’t worry about it. Bottom line is your shop seems to have done it so I would talk to them about why they did it before changing anything. It is not going to hurt anything in the meantime.

Longer version. The last few years of the SC, Porsche was making changes to deal with emissions compliance while preparing for the ‘84-‘89 Carrera platform.

It was my understanding that the primary reason for the retard vac line on the dizzy was to retard timing at idle. The theory being that retarded timing at idle means the fuel burn in the cylinder is hotter which results in less pollutants. Hotter temps also helps the catalytic converter. If you’re sitting in traffic, you’re polluting less. The side effect is the engine runs hotter. That is the most likely reason your shop did it - i.e., to have cooler engine temps. If you live in a hot climate and sit in rush hour traffic a lot, then hotter engine temps would be a bigger concern. It is an air-cooled engine after all. No air flow, no cooling.

As strlj points out there is apparently another reason - the timing is retarded when you come off the throttle.

My confusion was in the word choice. The advance vac line is a helper to the distributor. There are weighted springs inside the distributor that increase the timing advance as rpms increase. The advance vac line adds additional timing advance over and above what the weighted springs can provide. This is the really important one of the two. If this isn’t working you don’t get max power when you really need it (best case) or you can have detonation (knocking). Depends on a variety of factors. This one absolutely must be connected and functioning correctly.
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'83 911 SC 3.0 coupe (NA)

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Last edited by tirwin; 04-29-2019 at 05:45 AM..
Old 04-29-2019, 05:32 AM
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