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dizzy advance/retard lines

I noticed that the 83SC engine I have has only one vacuum line to the dizzy and the idle retard is not hooked up (capped off). Does this make a difference in my idel control...today, the car is still being broken in from a top end rebuild , starts great, warms up graet abut once warm idle is at 1100 which is too high, I can check with my shop when they check their work (ie adjust valves/change oil) after first 500 miles but I thought I would get forum opinions too

Thanks

Bob
Old 04-22-2019, 07:25 PM
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It is not an issue. The purpose of the idle retard was to cause the cylinder temp to be hotter at idle to burn more pollutants. Basically it was for emissions. If you want your engine to run cooler, leave it plugged.

Member psalt posted about this quite extensively. If you want to read up more on it, search for his old posts.
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Old 04-23-2019, 01:24 AM
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Thanks Tirwin
Old 04-23-2019, 04:04 AM
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is the cold idle lower than that.

does it idle up or down once warm
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Old 04-23-2019, 06:33 AM
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cold idle is good and when warmed up it settles to 1100 which strikes me as 200 too high..probably just an adjustment is required post top end rebuild.
Old 04-23-2019, 06:50 AM
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so does it idle up or down as it warms up.
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Old 04-23-2019, 06:54 AM
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In reality, the vacuum retard was designed to increase throttle response while reducing emissions. It adds an instant 10 degrees of advance whenever you tip in the throttle at any rpm while helping your engine run cooler. I can't imagine why anyone would want to degrade their performance and cause their engine to run hotter, would you?

Them Porsche engineers kinda knew what they were doing...


Cheers,

Joe

Last edited by stlrj; 04-24-2019 at 05:35 AM..
Old 04-24-2019, 05:24 AM
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so now i am confused by above responses

the one vacuum currently hooked up is the advance (on left side of dizzy). now its being suggested its in my benefit to hook up the capped vacuum retard as well....i figured it was there for a reason but to date no one seems to think its necessary, but my engine runs on the cool side already due to top end redo including il cooler and external cooler repairs to lines and trmbone. SO sounds like it wont kill be either way i go?
Old 04-24-2019, 05:32 AM
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Quote:
Originally Posted by stlrj View Post
In reality, the vacuum retard was designed to increase throttle response while reducing emissions. It adds an instant 10 degrees of advance whenever you tip in the throttle at any rpm while helping your engine run cooler. I can't imagine why anyone would want to degrade their performance and cause their engine to run hotter, would you?

Them Porsche engineers kinda knew what they were doing...


Cheers,

Joe
Incorrect.

The vacuum ADVANCE adds additional advance beyond the weighted springs of the distributor.

The RETARD only affects idle.

Why in the world would you want to retard timing when you’re tipping in on the throttle???
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Old 04-25-2019, 11:31 AM
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so I am back at square one..do i rehook up that vacuum (83 sc engine) or not, if I do, will i need to make other adjustments
Old 04-25-2019, 11:51 AM
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Quote:
Originally Posted by tirwin View Post
Incorrect.

The vacuum ADVANCE adds additional advance beyond the weighted springs of the distributor.

The RETARD only affects idle.

Why in the world would you want to retard timing when you’re tipping in on the throttle???
Not exactly true.

Whenever you take your foot off the throttle while cruising at 5k or any rpm, as in shifting gears, it pulls the timing back 10 degrees (good for emissions and you'll never notice it) but as soon as you touch the go pedal you get an instant 10 degree kick and throttle response to boot.

Again, them engineers were dang smart!
Old 04-25-2019, 06:02 PM
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based on the last response, i makes sense to re-install that missing line.
Old 04-25-2019, 06:14 PM
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Quote:
Originally Posted by stlrj View Post
Not exactly true.

Whenever you take your foot off the throttle while cruising at 5k or any rpm, as in shifting gears, it pulls the timing back 10 degrees (good for emissions and you'll never notice it) but as soon as you touch the go pedal you get an instant 10 degree kick and throttle response to boot.

Again, them engineers were dang smart!
Your post is very confusing.

The ‘83 dizzy has two vacuum lines. The retard and advance. Agreed? Your previous statement made it sound like retarding timing when increasing rpm is a good thing. The RETARD line doesn’t ADD advance. I don’t understand that logic at all. Letting off throttle is one thing, and I guess I can see where the retard would kick in when lifting off the gas, but retarding timing when increasing rpm makes no sense at all. Please educate me. You always want the advance vac line connected, which is not what we are debating.
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Last edited by tirwin; 04-25-2019 at 09:17 PM..
Old 04-25-2019, 09:10 PM
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Lord...so may varying opinions...i agree engineers knew what they were doing but in this day and age with all the smog devices removed etc, is that advance rally necessary or just leave the port capped?
Old 04-28-2019, 10:59 AM
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My translation: At idle, the retard is on. Tip into the throttle, the retard goes away, advancing the timing 10 degrees.
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Old 04-28-2019, 12:42 PM
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Quote:
Originally Posted by tirwin View Post
The RETARD line doesn’t ADD advance. I don’t understand that logic at all.
The second you are off idle you get the 10-ish degrees advance back that the retard function stole.

Retard does not add, it only takes away. However, I see what stlrj is intending. It "gives it back" quickly by falling out of the picture with off idle reduced vacuum.

Cripes. RDM said the same thing.
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Old 04-28-2019, 01:26 PM
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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...
Old 04-28-2019, 07:00 PM
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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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Last edited by tirwin; 04-29-2019 at 05:45 AM..
Old 04-29-2019, 05:32 AM
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Let us not forget, however, the German engineers that designed this genius device shared the same DNA that got us to the moon and may be difficult to comprehend.

Last edited by stlrj; 04-29-2019 at 05:48 AM..
Old 04-29-2019, 05:44 AM
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Tirwin...I really appreciate that explanation..and yes, I will leave as is and when i get to the shop for post rebuild checkup I will ask them about pros and cons of capping the retard line

Thanks!
Old 04-29-2019, 07:35 AM
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