Since 911SC does not have a chip, would advancing the timing help.

[Elombard]

Any way to do the timing like this with a light that doesnt have an advance knob?

[speeder]

Elombard, You would have to somehow make a mark on pulley exactly 35deg. BTDC, (don't know why Porsche did not do this on these cars; they did on earlier 911s), probably have to remove pulley to do this accurately. P.I.A.

As to the people who have disconnected their vacuum advance because it "ran crappy with it", there is something wrong w/ unit or vacuum path, (incorrectly routed?), and you will not get 35deg. total w/o it unless you have advanced your timing at idle beyond its optimum for lower RPMs.

My distributor advance works properly on my (previously) stock SC, I get 35deg. total w/ idle set at factory spec. (5deg.ATDC @ 800 rpm). Set timing at idle to factory spec, THEN check total adv., if it is not within spec/guidelines, (there is a small +/-, 2-3deg.?), figure out what is not working! This is not rocket science, and if you want car to perform the way it was designed to, don't Mickey Mouse it. Ignition timing is CRUCIAL to performance throughout the RPM range.

Lastly, a stock SC with timing/mixture/etc. on the money should not ping on 87 octane. Mine didn't w/ 35deg. total adv., even with today's lousy fuel, (especially in CA.). If it does ping, figure out why and correct the problem, they should not need higher octane fuel than they were designed for, and there is NO benefit to running higher octane than what a given motor requires, FWIW. This is one of the most persistent misconceptions in all of motoring.

[RazorRacer]

Elombard,

I took a micrometer and measured from Z1 to 5. Using that setting and red nail polish, I measured and marked 15, 25, and 35. Sears sells an adjustible timing light, too.

Speeder,

I have checked the vacuum hose connection and even replaced the vacuum advance unit (it wasn't broken). My best guess is the distributor weight springs are weak and don't require vacuum advance.

Compared to how it was running when I purchased it, I'd say it's doing great. I spent about 6 months with this BBS figuring out what was wrong. I plan to enhance the performance further, but for now I want to enjoy some p-car driving.

Also, there is a difference between Mickey Mouse and learning.

[MotoSook]

Dennis, Razor and I went through some major trouble shooting of our vacuum advance some time back, see :

close, but no cigar


Hey Razor. Good to see your handle pop up.

[MotoSook]

Dennis,

The vacuum advance does not provide that much advance. When I bought a new one, I tested it with a vacuum guage in line. I'll have to reread the thread, but I think I got less then 5 degrees advance from the v-unit. Setting your idle timing at 9-10 degrees BTDC would compensate for the v-unit and get you to 35-36 degree total.

It works fine so far.

Souk

[emcon5]

Originally posted by emcon5
Yeah, they don't say how it works. All they say is that the stock system has no provision for mapping the timing, and their system does.

OK, I got an email back from Milford, the guys who make the K-star thing. They say:

K-Star picks up the signal from the CDI unit (the igntion computer) and alters it.

I assume it monkeys with the signal from the magnetic pulse generator in the distributor, which sends the signal down the infamous "green wire". How this changes the ignition timing, I guess I don't understand.

Wouldn't any particular plug still fire when the rotor is contacting the connection for it's wire?

There must be more to this than I realize.

Tom

[Bones]

Originally posted by emcon5

OK, I got an email back from Milford, the guys who make the K-star thing. They say:

I assume it monkeys with the signal from the magnetic pulse generator in the distributor, which sends the signal down the infamous "green wire". How this changes the ignition timing, I guess I don't understand.

Wouldn't any particular plug still fire when the rotor is contacting the connection for it's wire?

There must be more to this than I realize.

Tom

h i Tom
i've found two three page articles on the 'k star' system.. i can't post because i don't have permission and i don't want to create any problems ....email me with your email and i'll scan and send them ....is .jpg or .gif ok for you?

[emcon5]

Thanks for the articles Bones, (And indirectly, Keith if he is reading this ).

The article says the K-Star fuel injection mapping portion works by varying the system control pressure. This sounds a lot like the Frequency valve found in the standard K-Jet with Lamda found in 80-83 US market 911SC's. The Main difference being that the K-star is mappable, and the K-Jet/Lamda uses an O2 sensor. That part makes perfect sense to me.

Unfortunately there is no information on how the timing is changed by their system, only that it can be.

Tom

[diy83sc]

It may have been Superman in a separate post that said if a lift or pull of the throttle plate smooths out the idle, the engine is either running lean or rich (i forget which.) Since I don't have access to a CO meter, can I use the same check to see if I am in the ballpark before I go ahead and make the 35 degree adjustments and disconnect the oxy sensor, or do I just simply bring it to my mechanic and have him set the distrib?

Tony

[Superman]

Yes, you can sometimes identify a lean or rich mixture by gently pusing or pulling on the air flow sensor plate while the engine is running. If idle improves by pushing up, then it is running too lean. Vice versa. but these systems are actually more sensitive than that. I have set mixture 'by ear' a lot of times and can usually get it close (I think JW was mildly impressed that it was so close), but I still feel that a "sniffer" is the way to set these. So yes, I'd suggest taking the car to a tuner. The entire process takes John about ten minutes if he dawdles. Much quicker if he were in a hurry, so don't go to somebody that thinks this is a two hour operation. Also, you'll need to find someone who is willing to set mixture at 3.5%. That's not factory spec.

There seems to be nothing wrong with my vacuum or mechanical advance. I removed and disassembled my distributor at one point, for nothing. And still, to get 35 degrees full advance the timing is about 7 degrees advanced beyond factory. There is no hint, whatsoever, of pinging at idle or redline. None. So, I am wondering if Denis' factory spec timing was done with the vacuum hose attached. I think leaving the vacuum hose attached (this is not factory procedure) would erroneously suggest that my timing is at 5 degrees BTDC.

The additional advance makes a significant difference in performance.

[speeder]

I don't remember right now whether you check it w/ hoses attached or not, also don't have Bentley manual here. (It is sitting on disassembled 911). But I do remember that I set it however the spec says, then checked advance w/ my mega-buck snap-on digital T. light and it maxs out @ 35deg. BTDC. I also checked my vac unit w/ a vacuum pump, both sides working, replaced lines, etc. Car started and ran flawlessly hot or cold, even with a few motor issues that are getting fixed now, (head studs, etc.), it helps a lot if CIS is operating correctly, of course.

It is my understanding that vacuum advance affects timing at RPMs significantly lower than red-line, (off idle to mid range), so even if you set your car to 35deg. total w/o vac working, you will not get proper advance and peak H.P. in the lower regions. This is the problem, not wide-open-throttle.

[diy83sc]

Left coast, thanks. I need to read up on adjusting the mixture first, think about doing it myself, finally ask myself if it will make for a better drive than it already is... but I can always go go back can't I

[Superman]

The '83 SC, and I'm pretty sure the '82 SC too, timing is done with the hose disconnected. Should be 5 degrees BTDC. With my hose disconnected, timing is at 12 degrees BTDC, and full advance is 35 degrees. Doug Z can verify that it has quite a bit of low end torque (really, a bunch with the 20/21 cams) and quiet as a mouse. No explanation.

There is a way that mixture can be set without a sniffer. If you have a dwell meter. There is a round plug going to nothing behind the engine compartment fuse box. It has three prongs. I believe you want the green one. Hook your dwell meter to it and a ground and set the dwell meter to "4 Cylinder." O2 sensor plugged in and working. The reading should cycle back and forth, centering on 45 degrees of dwell. Too high, and the mixture is too lean. Too low, and the mixture is too rich.

[Doug Zielke]

Originally posted by Superman
Doug Z can verify that it has quite a bit of low end torque .......

It's like a tractor off the line.
Then, around 4000rpm, the afterburner kicks in!
Love those 20/21's, eh Jim?

[Speedy1]

Well there is a lot of conflicting issues here. My 82sc was smoged by the P.O. and, a week later I started to fix things that didnt work. The motor had a surge problem a miss at idle the rpm's would climb up when hot and very slowly come back to around 950 rpm's, and no cruse control. Well it ended up being a vacume leak, the small hose that comes from the throtle body to the T and to the cruse was broken. also the large hose that goes to the cruse is broken and still is (need help with that one also. What does that one do?) Anyhow how did it pass smog the timing was on the first mark on your left of the pulley and it had a broken vacume line. when I fixed the vacume line I had to readjust the idle so I checked the timing and it was retarted so I bumped it just a R.C.H. past the mark to the right well it ran like a champ but it pinged a bit so I backed the timing back a bit and it is ok now. I don't know where the timing is but it is smoother and idles good but it surges a bit. I replaced the plug wires with new stock ones. replaced the vacume lines and the T. All is good! How can I tell if the fuel ratio was set lean or rich by the clown who smoged it?, because he did not fix the vacume leak, or the shorting stock plug wires. What are the pros and cons for unpluging the O2 sensor? Will the OX lamp come on? Can I unplug the relay under the pass seat instead? Will my cruse still work? Will it kill the fuel economy? Is the timing set with both vacume lines disconected? If not which one gets disconected? What will I gain if the timing is set to achieve 35* total advance with the oxygen sensor disconected and proper air/fuel mixture? 5 -10 Hp? Is that asuming a 3.5% air /fuel mixture. and can that be set by the dwell meter technique?
MORE details please!

[bigchillcar]

JW,
While we're on the topic, what do you recommend for a setting the timing procedure for a '74 with a 2.7 (straight 911 without s-cams)?
Thanks,
Ryan

[curlesw]

Any chance of someone writing a Technical Article, complete with pictures, on this topic? It wolud be VERY helpful as I'd like to do this but have a hand full of thumbs....

Wayne C
83 SC