Ignition Timing

[Helmsy]

I want to check my timing and adjust (if necessary) so would like to know your procedures for checking timing (I have a Euro model).

In the manual I have it says to check timing (for a 930/66):

USA 1 +/- 2degs at idle (950rpm +/-) Vacuum Hose CONNECTED

Euro 2 +/- 2degs at idle (950rpm +/-) Vacuum Hose CONNECTED

And to adjust timing:

USA 26 +/- 1deg BTDC at 4000rpm Vacuum Hose DISCONNECTED

EURO 29 +/- 1deg BTDC at 4000rpm Vacuum Hose DISCONNECTED

I want to check my vacuum unit on the distributer is working properly so would like to know how you guys adjust your timing and if there are any hints and tips to getting it just right.

[930turbo]

I have a '77 3.0. Mine is set @ idle vacuum retard connected, 5 degrees ATDC. I gain about 500 revs if I disconnect the vacuum hose indicating that it's working.

[les_garten]

Originally Posted by Helmsy

I want to check my timing and adjust (if necessary) so would like to know your procedures for checking timing (I have a Euro model).

In the manual I have it says to check timing (for a 930/66):

USA 1 +/- 2degs at idle (950rpm +/-) Vacuum Hose CONNECTED

Euro 2 +/- 2degs at idle (950rpm +/-) Vacuum Hose CONNECTED

And to adjust timing:

USA 26 +/- 1deg BTDC at 4000rpm Vacuum Hose DISCONNECTED

EURO 29 +/- 1deg BTDC at 4000rpm Vacuum Hose DISCONNECTED

I want to check my vacuum unit on the distributer is working properly so would like to know how you guys adjust your timing and if there are any hints and tips to getting it just right.

I have an '85 Euro and I've always timed it like in RED here. I used that as a little insurance against detonation or a tank of bad Gazz. I don't much care what it is doing at Idle.

.

[A930Rocket]

I time my 87 at 4000 rpm.

[billjam]

This subject has me puzzled as well.
What timing is best to use if your motor isn't strictly US or Euro?

For example, I have an 86 US car (930/68) and I have deleted all the emissions control stuff (smog pump, O2 sensor, cat, etc.) and most of the cold start gizmos. It has SC cams and the dizzy with boost and vacuum ports.

In the Porsche manual (page 28-2b) it gives the following values:
Europe, ROW: 29 degrees before TDC at 4000 rpm (with vacuum disconnected)
USA: 10 +/- 2 degrees after TDC at 1000 rpm
California, Japan: 5 +/- 2 degrees after TDC at 1000 rpm

I have only recently put this engine back together after a major rebuild. I've played with a few settings and have settled on about 7 or 8 degrees ATDC at 1000 rpm and it seems to perform OK, but I don't know if this is the optimum.

Comments??

Can anyone explain why the Europe and ROW models are timed at 4000 rpm and not at idle?

[beepbeep]

Originally Posted by billjam

Can anyone explain why the Europe and ROW models are timed at 4000 rpm and not at idle?

Knock insurance. 930 engine is low C/R design that is unlikely to develop any boost at idle. Knock will occur where torque/VE is highest (around 4000 RPM).

That's why you want to be dead sure that advance is absolutely correct around 4000 RPM. If it's incorrect at idle, it will mess up emissions and do other stuff but it won't destroy the engine.

[maximo]

Originally Posted by beepbeep

Knock insurance. 930 engine is low C/R design that is unlikely to develop any boost at idle. Knock will occur where torque/VE is highest (around 4000 RPM).

That's why you want to be dead sure that advance is absolutely correct around 4000 RPM. If it's incorrect at idle, it will mess up emissions and do other stuff but it won't destroy the engine.

good information !

[930turbo]

You can check both. The total advance is important for detination as others have indicated, however, the idle setting is important for more than just emissions. Your intake vacuum at idle will vary significatly with initial timing. Intake vacuum has an influence on mixture via the control pressure regulator. For example, if your initial timing is too advanced, your vacuum will be above design and cause the mixture to go lean. It is best to have the timing correct on both ends of the curve to avoid compromising other things in your quest for the perfect tune.

[jwasbury]

Originally Posted by 930turbo

Intake vacuum has an influence on mixture via the control pressure regulator. For example, if your initial timing is too advanced, your vacuum will be above design and cause the mixture to go lean.

FWIW, I tested my Control pressure regulator (WUR), and found that it does not respond to vacuum, only to boost. This is on my '79 US model.

[billjam]

I guess what all this really means is that if timing is set around 5 to 10 degrees after TDC at idle, it should also be about 29 degrees before TDC at 4000 rpm (with vacuum disconnected) if everything is working OK.
Correct?

[les_garten]

Originally Posted by billjam

I guess what all this really means is that if timing is set around 5 to 10 degrees after TDC at idle, it should also be about 29 degrees before TDC at 4000 rpm (with vacuum disconnected) if everything is working OK.
Correct?

That ain't how I'd do it, and I wouldn't make that assumption. How about put your light on it, run it up to 4000, dial in your timing and you're done? What's wrong with doing it that way?

.

[A930Rocket]

Thats how I do it.

...How about put your light on it, run it up to 4000, dial in your timing and you're done? What's wrong with doing it that way?
.

[Helmsy]

So if I run at 4000rpm disconnect vacuum and dial it in and then find that it isn't right at idle with vacuum connected then I can presume I have a faulty vacuum unit on the dizzy?

[les_garten]

Originally Posted by Helmsy

So if I run at 4000rpm disconnect vacuum and dial it in and then find that it isn't right at idle with vacuum connected then I can presume I have a faulty vacuum unit on the dizzy?

How about a distributor from another car/series? Anything is possible. These cars/parts are old and all portions of the distributor/ignition system should be inspected regularly for function. Advance springs, plate movements advance retard mechanisms, etc.

[e170drvr]

Yes, Assuming you have the correct distributor connected properly set with the proper timing at 4000 rpm, also proper idle speed you should be in spec, otherwise your distributor probably needs some freshening.

[930turbo]

Your '79 has two ports, one vacuum and the other boost. The port on top is influenced by vacuum, the port at the base/front is boost. This allows the vacuum to lean slightly under light load and enrich slightly under boost.

FWIW, I tested my Control pressure regulator (WUR), and found that it does not respond to vacuum, only to boost. This is on my '79 US model.

[930turbo]

The timing needs to be correct at both ends. You're checking two things during this tuning exercise, the total advance and the mechanical advance - or more importantly - mechanical retard @ idle. I just had an example this past weekend. An '83 SC that would not idle down below 2k when the total advance was set to spec. The distributor was at fault. It did not return all the way to initial due to sticky internals. I only had about 18 degrees of mechanical advance instead of 23.

[fredmeister]

You should really check the entire function under vacuum and boost.
I found that idle timing of anything ATDC or even 0 degrees BTDC yields horrible off idle and low rpm performance. I could run faster than the car until 2500rpm.
It is important to limit advance to under 29 degrees at 4000rpm because detonation is the worst thing to happen to your engine. However, you don't want to get disappointed at low speeds if this forces a bad idle timing.
That being said, I time my 79 930 with the vacuum and boost hoses on my dizzy the following way.
Idle speed 950rpm timing to 4-6 degrees BTDC with vacuum hose connected. Remove the hose and see how far advanced it goes. This tells you how much vacuum retard the can is producing and check against specs from the workshop manual. If it don't work fix it.
Then I reconnect it and remove the boost hose and supply pressure to it with a small pressure hand pump and see how much it retards timing. This checks that the boost retard is working and how much you get.
Then run it up to 4000rpm and set the timing with the knowledge that under boost (when under load, not when checking it in the garage now) it will retard back that amount. This should be around 26-29 degrees max from what I see normally.
This gives me a good running car at low rpm around town and pulls hard when boosting.

I really wish some tuner experts would publish a timing chart that we could use for setting up our cars. Most of us here by now have modified the cars with k27 turbos and headers and a little more boost and I would like new data to go by that works.
I don;t want to destroy my engine until I find out the hard way. Plus who knows what distributor is on their 30 year old car, me being the 4th owner and being that Porsche supplied a few different versions over the years. California, US, ROW etc.
Which one has the ultimate advance curves and vacuum/boost retard features? lots of questions!

[jwasbury]

Originally Posted by 930turbo

Your '79 has two ports, one vacuum and the other boost. The port on top is influenced by vacuum, the port at the base/front is boost. This allows the vacuum to lean slightly under light load and enrich slightly under boost.

FWIW, I tested my Control pressure regulator (WUR), and found that it does not respond to vacuum, only to boost. This is on my '79 US model.

AFAIK, there is only one port that goes to the Manifold on my WUR (which is the correct p/n for a '79 US), the port on top is a vent which is plumbed to the airbox.

[e170drvr]

Fred, are you saying that you set your timing at 4000 rpm boost hose disconnected. so that it is advanced from your target value by the number of degrees of retard you were able to get with the hand pump?