PorKen

(US models)

Years 3K -Idle- IdleRPM Notes
78-79 31 00-04 800±50 0,3
80-82 23 08-10 750±50 0,1,4
83-84 20 04-08 650±50 0,1,2

Max advance (vacuum hoses removed)
78-79 <=36 @ 5K
80-82 29-34 @ 6K
83-84 28-30 @ 5K

Notes
0. Idle RPM with hoses attached
1. 3K, idle advance with hoses removed
2. Distributor has vacuum advance only, no vacuum retard
3. 3K advance hoses removed, idle advance with hoses attached
4. Distributor vacuum control range is changed from 81, 140-240mbar to 360-470mbar

GlenL

Thanks, Ken. I Read the Fing Spec Book (RTFSB) which doesn't have all those models.

hacker-pschorr

I'm still confused why the variance. The owners manual for my 79 & 81 list 87 octain as the minimum for fuel. So these numbers are VERY conservative. Also consider this is based on late 70's fuel qualtiy.

Jean-Louis has his euro track car set to 31-32 degrees at 3,000 - hoses removed on his supercharged track car with no issues (3 day weekend, two drivers, 24 sessions so far). This is 5 pounds of boost, no intercooler running half / half 92 & 110 octain fuel.

So what I'm trying to understand is why the factory had such a variance over the years with the exact same ignition system on all the cars. Yes the displacement changed a little 83-84 & the cams changed slightly. The cam difference between 80-84 is hardly even a factor.

hacker-pschorr

Just made a cool discovery (assuming I did this correctly). With only the advance port hooked up (stock) and the retard line plugged / disconnected:

5lbs of boost ignition is retarded by 7 degrees.

toofast928

That's cool. So we can add on initial advance.
What happens if the retard vaccum hose is connected? Does boost pressure in the advance and retard hose equalize?

hacker-pschorr

I just tried that tonight - first starting at 23 degrees @ 3,000 for a stock base line run. It bogged a bit above 5,000rpm a few times. I pulled over, advanced it a bit - maybe around 26-27 based on my cheater marks. Now it's almost perfect. Wednesday on the Dyno we will be able to really dial this in.

What have we learned here? On big boost applications with 16V 928's we can easily control ignition advance under boost. There are small check valves one could buy to control max retardation / advance to stick inline for complete control.

With the discovery of how easily timing can be controlled under boost. The GB Blower wrecking crew is talking about building a no-holds-barred 16V just for the hell of it. Not sure yet if they are thinking my car is the test dummy......hope not. These 16V cars are so cheap to find good runners, trying to stretch one out to 400+rwhp soulds like fun. I have a feeling this will be a project on the table within the next year.

Anyone see Herr-Kuhn around? He was actually the reason I started down this experimental road of playing with the timing vacuum lines. So credit for kicking off this idea is all his.

WOT my rear tires will not hook up anymore, rolling or launching. Guess I need more than 255/40-17's back there.

SMTCapeCod

Ooh, more info on cam advance, please? Were you the person that used the Benz woodruff keys?

IIRC, the FSM and the tech book differ with regard to the recomended timing on my '83 Euro. Not significantly, it just caught my eye some time ago.

I've got low hours on it, but my MSD offers (well, could offer) a lot of different capabilities with add-ons: soft rev-limiting, boost indexed timing retard, rpm switched accessories (like Naws), knock sensor etc. Too bad the forced induction part is absent on my car...

toofast928

So Hacker your saying the best set up for the 16V SC is to disconnect the retard hose to the distb. And set total mechanical timing to 27-31 degrees, 3000 RPM. Each 1 PSI of boost will retard timming 1 degree, roughly................

Hmm I could advance another 5 deg.

hacker-pschorr

None of this is dyno tested so do whatever you want at your own risk.

What I did was hold the motor at 3,000rpm then added 5psi of pressure to the advance side of the diaphram. I then turned down the dial on my timing light - total advance went from 31 degrees to 25. Results could be different at 6,000 - I did not test that.

The person (Herr-Kuhn) who suggested this idea in the frist place also suggested shortening the rod that goes into the distributor from the vacuum diaphram. Changes the leverage & overall results.

As far as my car is concerned - I have a different problem. With timing at 30 degrees @ 3,000 with both lines hooked up stock, it's still cutting out like before. I have a new coil coming tomorrw and two spare ignition moduals to try next. This is weird.

toofast928

Could the cut out be from spark plug blow out? Did you try increacing the spark plug gap?

hacker-pschorr

Increasing the gap? Typically with boosted motors you close the gap.

Is your car still an L-Jet? What fuel pressure are you running & where do you have timing set to?

toofast928

I ment try increasing the spark increase plug gap from .028" to .032. But I gues it doesn't make sense for SP blow out.

Yes still L Jet, looking to convert to MAF.
My fuel pressure is 38 at idle, maxes to 80 psi at 6 pds boost. Total Timming 25 degrees at 3000 RPM. Your specs the same?

Did you monitor the O2 sensor for a rough idea what the A/F ratio is.

toofast928

Hacker?

hacker-pschorr

What?

Oh - air / fuel per the gauge looks good now that I have fuel pressure in the right ballpark area. Before it actually didn't look bad (in the green). The car was bascially flooded so at least I didn't run it stupid lean and pop the motor. Fuel injector cleaner is in my near future - after todays dyno test (3rd timet he charm?)

Spark is at .023 right now - running fine - no buildup after a few days of city driving on a colder plug.

toofast928

Ok so at least open the SP gap to .028.
When you say fuel pressure is in the ball park, what's the max reading?