Setting advance on an 83 SC: final word ?

[Demetri]

Your engine has higher (9.8:1) compression and was tuned to run on 98 RON with 25 BTDC max ignition timing. 98 RON is around 93 CLC octane fuel. Unless you are a magician, you can't run the engine on lower spec fuel with 10 degrees more advance, than the factory could. The answer is you need to raise the octane of the fuel or reduce the timing. Your distributor should only give 20 degrees of mechanical advance, so I would first check it is the right part number, then question your measurements. You also want to check the AFR at WOT to make sure it is not too lean. The only ways to lower the octane requirement of your engine is to improve cooling, lower the intake air temp, or get the oil mist out of your intake.

psalt-

I am not Houdini. My timing is set at 25 BTDC. This is all consistent with my observations. Running it rich at 2 TDC takes care of the knock most of the time. Less chance for knock on cold days and higher chance on hot days. 100 octane gas takes care of it, but it is spendy.

Can anyone recommend a good octane boost?

This thread has been a big help. Thanks guys!

[wolfswest]

Hi guys,

yesterday me and my buddy changed the oil and filter on my sc and out of curiousity we checked the timing of the ignition. we disconnected the advance and retard line and plugged them and we saw that the advance was way more at idle then it should be (stock porsche recommendation) don't know the degrees but the mark was way to the left, so we dialed it in at 5 degrees, put the lines back on and I drove home: the car was remarkably less sportive. So I want to reverse the setting and I started reading here, a few questions here:

2) Others, including some fairly famous mechanics on this forum, generally recommend setting advance to 32-35 at high RPM and letting the idle fall where it may - generally higher: like 10 to 12 degrees. I did that 10K miles ago, I think I ended up at 32 - since I could hear it ping at 35D under WOT and backed it off a bit - and my idle was 10D BTDC with the retard line off - logically 20 degrees less than 5000 RPM which is the range of an SC distributor. My car ran well enough (it did not self destruct, at any rate) and importantly, it ran much cooler than before.

=>okay, let's say I dial it in at 5000 rpm at 32 degrees like suggested in the first post, that's something you do with the vacuum lines disconnected and plugged? right?

=>Since you can't test the vacuum advance without load (blipping the trottle in the garage isn't the same if I believe most of the posts here) , is there a possibility that at some point, not WOT, because there is no vacuum at WOT, it even advance more then 32 degrees?

Or are the degrees that I choose at 4-5-6000 RPM (let's say 32 degrees) with the tubes disconnected while fine tuning the most the distributor will ever have under load while driving??

I hope everybody understands my questions, english isn't my native language.

thx,

Dem

[Lorenfb]

Most on this thread need to consult the 911 3.2 guys, as they use those performance
chips that run the timing into the high 30s. So based on what they're doing with the
timing on their engines, advancing beyond the Porsche spec should be no problem, right?
Remember the 911 3.2 is just a 911SC with a longer stroke.