82 SC - disconnecting advance retard?

[ohecht]

I have set my total advance to 35 BTDC, and the car is running great, with only the idle varying slightly (and worse fuel economy). All of the fuel settings (pressures, mixture) are right.

I would like to try and run without the vacuum retard at idle to see if that helps smooth the idle. Is there any danger to this? Does that vacuum connection do anything other than slightly retard the timing at idle?

I searched, and it seems that some run this way, but there are a lotof ariations between model years and I did not see anything for an 82 running 35 total advance.

Thanks,

Olivier

[stlrj]

Disconnectiing the retard will lose you some throttle response. The vacuum connections are there to speed up the sluggish centrifugal advance mechanism and, of course, for smog.

[ohecht]

Does that apply to the retard mechanism, too? My distributor has both vacuum advance and retard, and I would leave the advance line connected.

Olivier

[stlrj]

Ain't nothing retarded about the retard! It just dumps the 10 degrees of retard as soon as you crack the throttle for an instant 10 degrees of advance which does wonders for throttle response.

Joe

[ohecht]

OK, that does make sense.

Thanks,

Olivier

[moosthuizen]

Olivier

Im new in the game. Mind explaining to me what you did, how and why. I have a '80 911 sc, can I do it on mine as well? I set my timing at 5 BTDC. What is this you did ot 35 BTDC?

Marius
'80 911 sc

[ohecht]

I did nothing to the vacuum lines after getting this advice, since I was forgetting the effect of the instand advance from opening the throttle.

The best advice I have seen for setting the mixture and timing for a SC, since the factory specs are more for emissions than performance, is from John Walker's Workshop. John is an expert with his own shop, and you can confirm all this information by searching for his posts.

I set the mixture on the rich side to 3.5% CO with a Gunsten Gastester (costs about $130). Rather than follow the regular directions of setting the timing at idle with the hoses disconnected, etc. (there are also a lot of differences in the dist advance/retard mechanisms even amoung the SC years, so you should refer to your own car's data plate), JW's advice is to just set the total advance to 35 degrees BTDC. There is no mark on the pulley for this, so you will need an adjustable timing light, and you just set it at high RPMs, when all the advance mechanisms in the distributor are "maxed out". Listen for detonation, and back off if you hear any. The fact that all the advance mechanisms are at their limit is why it's called "total advance". You do all this with al the vacuum lines connected. What you did to set to 5 BTDC at idle is fine, too, you just set the beginning point for the advance curve, while I set the ending point. The overall timing is still usually in the same ballpark.

I did the mixture first, since a richer mixture will resist detonation more. I went right to 35 degrees total advance and never heard any detonation. My car s running stronger than ever, the only side effect I have noticed is poorer fuel economy, which is a trade off for the rich mixture and extra power.

[UTKarmann_Ghia]

Nice explanation Oliver. BTW, hows the tranny working for you? Mine is shifting like BUTTER

[ohecht]

Mine is running well, which seems like a small miracle based on what was lying on my workbench 2 months ago!

It sticks occasionally in gear (very slightly), but nothing major. Mostly 3rd and 4th, which I think are taking longer to break in (and I reused the hub on that set).

It worked really well before the rebuild, with only the 1st syncro as an issue, so I have a fairly high standard to compare it to.

Olivier

[john walker's workshop]

so you remove the vacuum retard hose and the idle advance goes up to "whatever". the total advance does not change, or the built in mechanical advance curve thru the rpms. or you leave the hoses attached, and as soon as the throttle opens, the advance goes to the same place as if you didn't have the retard working, and the mechanical advance takes it from there. so what's the difference. you don't get any extra power from the retard releasing, in other words. both basically start in the same place. hose off gets you a smoother idle, but the idle speed goes up with the advance in timing and has to be turned down, which affects the previous idle mixture reading, so that also needs to be readjusted. the typical problem with doing this, is that the idle speed screw may bottom out before getting the idle speed turned down to the 950-1000 range. also, retarded timing at idle produces less hydrocarbons.

[stlrj]

the advance goes to the same place as if you didn't have the retard working, and the mechanical advance takes it from there. so what's the difference

The difference being the instantaneous advance that dumping the retard results when cracking the throttle that the slow moving mechanical advance could never duplicate when getting on the throttle at any rpm.

A DME controlled ignition dumps the retard electronically with the movement of the air flow meter.

[ohecht]

I agree, and I did not disconnect any of the hoses due to this advice. I think my air sensor plate may be dirty or slightly out of adjustment, as it seems that the inconsistent idle is related to the fact that the idle dips low after closing the throttle (sometimes).

On a scale of 1-10 in terms of annoying CIS problems I have had and usually fixed, this is about a 2.

Olivier

[john walker's workshop]

if you remove the vacuum from the retard, the timing advances to say, 10° initial. with the hose connected, if you open the throttle just a tad, the vacuum drops and the timing advances to 10° initial. there is no actual difference in the mechanical function, and you get no power benefit from that instantanious advance, because both ways start at 10°. the retard was only added to lower HC at idle.

[stlrj]

I agree no power increase but a noticable difference in throttle response with the retard connected.

[moosthuizen]

Thanks Oliver, you realy explained it well. Im learning a lot, and with your explanation I've gained more knowledge.

Seems you sorted out your troubles

Marius
'80 911 sc

[William Miller]

JW, I have a 83 ROW k-basic CIS. It's a bastard case because the block is an 82 US 930-16.
After a lot of searching I now have all the ROW CIS parts back on the engine except for the dizzy.

After reading these last few threads I have answered a lot of my questions.

The ROW dizzy was simular to the early SC with no vac retard.
I've never seen the ROW distributer curve. I've herd roumers that people re-curve to that as a benchmark. Is the roumer true? Is there any difference? Is there anything I'm missing?

Should I just set timing as described above and be done with it?

[William Miller]

BTW, I also can't find the ROW rev limiting rotor. I've herd that the turbo rotor fits and is avalible at our host.
Part number H602-901-01 7000 rpm

The ROW is 602-901-02 6800rpm.

Will it work? Any comments?

[dimps8]

It maybe a tad harder to start with it disconnected, at 10 deg.

[john walker's workshop]

until it starts, and a vacuum is created to actually retard the timing, it will be 10°, hose off or on, when the starter is cranking.