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-   -   dizzy advance/retard lines (http://forums.pelicanparts.com/porsche-911-technical-forum/1027488-dizzy-advance-retard-lines.html)

7783911 04-22-2019 07:25 PM

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

tirwin 04-23-2019 01:24 AM

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.

7783911 04-23-2019 04:04 AM

Thanks Tirwin

T77911S 04-23-2019 06:33 AM

is the cold idle lower than that.

does it idle up or down once warm

7783911 04-23-2019 06:50 AM

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.

T77911S 04-23-2019 06:54 AM

so does it idle up or down as it warms up.

stlrj 04-24-2019 05:24 AM

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

7783911 04-24-2019 05:32 AM

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?

tirwin 04-25-2019 11:31 AM

Quote:

Originally Posted by stlrj (Post 10437402)
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???

7783911 04-25-2019 11:51 AM

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

stlrj 04-25-2019 06:02 PM

Quote:

Originally Posted by tirwin (Post 10438858)
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!

7783911 04-25-2019 06:14 PM

based on the last response, i makes sense to re-install that missing line.

tirwin 04-25-2019 09:10 PM

Quote:

Originally Posted by stlrj (Post 10439259)
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.

7783911 04-28-2019 10:59 AM

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?

RDM 04-28-2019 12:42 PM

My translation: At idle, the retard is on. Tip into the throttle, the retard goes away, advancing the timing 10 degrees.

Bob Kontak 04-28-2019 01:26 PM

Quote:

Originally Posted by tirwin (Post 10439394)
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.

7783911 04-28-2019 07:00 PM

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...

tirwin 04-29-2019 05:32 AM

Quote:

Originally Posted by 7783911 (Post 10441934)
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.

stlrj 04-29-2019 05:44 AM

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.

7783911 04-29-2019 07:35 AM

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!


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