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sudo apt-get purge 930
 
equality72521's Avatar
 
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Quote:
Originally Posted by RarlyL8 View Post
Mark, you may see in the notes I sent you that I lock my distributor, which is the same as yours, down at 26* @4000rpm. The reason for this and not 29* is so I can safely use poor grade gasoline in the hot summer. I made the assumption that the specification of 29* in my 1978 manual was for European grade fuel available to the public in 1978. I have never had an issue with detonation and my engine is very healthy after 10 years of flogging the crap out of it.
Just follow what it sais in the manual and you will be good to go.
Yeah, I plan on 26 but I wanted to quote the manual exactly as written.
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Mark 1979 930 Euro ***GONE AND DON'T MISS IT AT ALL***

"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
--clutch-monkey
Old 04-02-2010, 04:49 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #81 (permalink)
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Quote:
Originally Posted by mark houghton View Post
Which still begs the question, why not US also? Surely not emissions related. I won't be comfortable with this until the answer is clear.
I don't like to speak generally for all cars, as there are 4 different distributors out there, but let's take the case of a 1978 to 81 USA (California) car.

USA (California) - It is timed at 31 nominal at 4000 rpm with the vacuum hose disconnected. It has 16 degrees of centrifugal advance at 4000. That means it has a static timing of 31 - 16 = 15 degrees.

EURO - For the Euro distributor the timing is 0 with the vacuum hose connected. At idle the vacuum retard is about 10 degrees, and the centrifugal advance at idle is 0. That means it has a static timing of 0 + 10 + 0 = 10 degrees.

So the USA has 5 more degrees static timing than the euro car. In order to maintain their safety margin Porsche decided that 5 degrees had to be pulled out under boost. That is why the USA car has boost retard. The boost retard is actually more than 5 degrees because the USA car also has more centrifugal advance. The boost retard is around 8 degrees.

Under full load both cars have the same timing:

EURO: 10 static + 12 centrifugal = 22
USA(California): 15 static + 16 centrifugal - 8 boost retard = 23

While I'm at it, let's explode a few more internet myths.

Euro cars have more timing under full boost - Wrong, as we have just seen.

Euro cars have a "more aggressive" timing curve - Wrong, the USA cars have more centrifugal advance, with about the same vacuum retard.

Euro cars had more timing because they had better fuel - Wrong in the late '70's US fuel was, on average, better than european fuel.

If you want more performance, get a euro distirbutor and pull off all the hoses - Wrong, the USA distributor can run more static timing safely with the boost retard feature, and it has more centrifugal advance. Just disconnect the vacuum retard hose.
Old 04-02-2010, 05:32 AM
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Quote:
Euro cars have a "more aggressive" timing curve - Wrong, the USA cars have more centrifugal advance, with about the same vacuum retard.
The curve has nothing to do with total timing. That is but one point on the curve.

Quote:
Euro cars had more timing because they had better fuel - Wrong in the late '70's US fuel was, on average, better than european fuel.
The octane rating in Europe at that time was greater than the 87 octane available in the US. Premium fuel was expensive and hard to come by. There is also the issue of US thermol reactors and the increased engine operating temperatures.

Quote:
If you want more performance, get a euro distirbutor and pull off all the hoses - Wrong, the USA distributor can run more static timing safely with the boost retard feature, and it has more centrifugal advance. Just disconnect the vacuum retard hose.
There is only one hose on the early Euro distributor, idle vac retard. My engine is a California model 1978. I didn't go to the trouble and expense to change out the distributor for no reason. The difference is noticeable stock to stock. When the distributor is modified the difference transforms the driveability. One of the services I would like to offer my clients is distributor tuning, there is a lot to be gained there.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 04-02-2010, 06:40 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #83 (permalink)
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Yes, the curve is important. The USA distributor provides 18 degrees by 2800 RPM. The Euro distributor offers 13 degrees by 3200. If you pull off the retard hose and "lock it down", I think you will like the USA distributor even better. It advances faster, and more. Be sure the advance weights move smoothly. The grease gets a little gummy after so many years.

I stand by my comment on the fuel octane. Professionaly, I have access to a large database that goes back to the '40's, detailing fuel quality, including octane, so I have more than wikipedia insight there.

Getting into the distributor re-curving business now would be like getting into the analog TV business now. Let's just say I wouldn't be investing! There are so many great options that include air temperature as an input. As we know, that is really key from a reliability viewpoint. Someone who posts on this board went to the Colorado parade with their distributor "locked down". Charging up I70 near Idaho Springs when the death rattle started. It will work, until you get into an environment where it doesn't.

Quote:
Originally Posted by RarlyL8 View Post
The curve has nothing to do with total timing. That is but one point on the curve.



The octane rating in Europe at that time was greater than the 87 octane available in the US. Premium fuel was expensive and hard to come by. There is also the issue of US thermol reactors and the increased engine operating temperatures.



There is only one hose on the early Euro distributor, idle vac retard. My engine is a California model 1978. I didn't go to the trouble and expense to change out the distributor for no reason. The difference is noticeable stock to stock. When the distributor is modified the difference transforms the driveability. One of the services I would like to offer my clients is distributor tuning, there is a lot to be gained there.
Old 04-02-2010, 08:27 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #84 (permalink)
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Disconnecting Vacuum Retard

The Vac-Retard connection to both style distributors works only at idle. With acceleration off idle it quickly goes away and timing jumps about 8 to 10 deg advance. So same same to this point for both distributors.

Vac Retard at idle seems to be mostly a smog function thought it can also help with making a motor easier to start. Running with it disconnected should help reduce operating temps at idle as the fuel burns more in the cylinder and less in the exhaust tract.

If it is disconnected, idle RPM will increase as the motor will be operating more efficiently but this can be brought back in line by adjusting the idle air bypass screw.

As the motor quickly bumps timing with loss of intake vac and acceleration anyway, running with this disconnected should not be a big issue. I also would not expect it to improve off idle response much though it might add a little crispness.

Performance is gained by timing being set at more ideal settings. Many have reported increased low end response with more initial advance. Disconnecting the Vac-Ret dose not really get any real added advance off idle.

Which distributor is a better for performance.

Both can be worked to provide equal performance under max acceleration and boost.

However, because the Double Pressure Box distributor has a boost retard function I believe it has the most potential to be a better distributor. I think even the later Euro 3.3's may have had a double connection pot.

If we agree peak safe acceleration is found near -26 deg on US fuel, the US dist can be set to run at that on boost. However, with this will come the ability to run a more desirable ignition advance of about -34 through -36 at cruse knowing the boost retard will pull timing back 8-10 deg when needed. (The C2 Turbos pull about 40 deg on cruse.)

This should lower cruse operating temps and increase gas mileage as the motor is operating at a more efficient and ideal point and getting more power out of the same amount of fuel.

What happens at idle if we just set total timing with 10 deg more advance?

It will advance idle timing the same 10 deg. With the Vac Retard working, timing with acceleration and loss of Vac-Retard would then quickly move from about -10 to about -20.

This may or may not be to aggressive. AFR will have some effect. If CO is set at 3.5% or an AFR of about 13/1 it might be ok. Some have reported being able to run this much timing off idle or by about 1500rpm. If this is to much initial advance then we would have to increase the range the mechanical advance operates over. If we add about 5 deg to the mechanical advance range (mod the stop) this would bring idle timing to about -5 at idle and quickly jump to -15 or such with acceleration. This should improve off idle response a noticeable amount and work for most.

Again, both can be tuned for peak HP and acceleration and will be equals in these areas. However, the dual pot because it has 'boost retard' capability can also run a more favorable advance at curse for better mileage and a cooler running motor.


Please be careful.

A motor that can run 12.2/1 AFR and -26 deg advance on boost is going to make more HP than a motor at a more factory spec of say 11.5/1 AFR and -17 deg advance on boost.

However, if the fuel system goes a little out of spec and one or more cylinders should go lean, one gets a tank of poor gas, or should one's motor become heat soaked from sitting at a light with the A/C on on a hot day-- the factory spec motor will be less likely to sustain any damage.

What we do not know is how much advance most of us can run to improve off idle response and on boost power. This will vary by motor depending on its actual compression, cams, intercooler, boost level, out door temps, and other variables.

JMO
Old 04-02-2010, 08:28 AM
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I think those are good insights. Just a couple of comments:

When the exhaust temps are reduced by advancing timing, turbo response degrades, so time to boost is affected.

Both distributors can give the same maximum timing, but without boost retard there is a negative compromise in what part throttle timing you can run. I think you recognize this well, I just wanted to underline it. Without some sort of manifold pressure feedback, the whole timing curve is compromised. If it is OK at full load, it won't be at part load, and vica versa.
Old 04-02-2010, 08:56 AM
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This board gets more like Rennlist every day. I apologize Mark for my part in destroying his thread.
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Old 04-02-2010, 10:11 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #87 (permalink)
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Quote:
Originally Posted by Speedy Squirrel View Post
Both distributors can give the same maximum timing, but without boost retard there is a negative compromise in what part throttle timing you can run. ...
SS, Thanks for the confirmation.

I to have wondered about heat and turbo response. I would hope a more ideal WOT timing and or AFRs' would out weigh any loss from storing extra heat at idle.

I seem to recall that when I did a Google on Vac-Retard that it is mostly developed as an emissions thing.

I am at times mistaken. That is how I learn.
Old 04-02-2010, 10:26 AM
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Oh ir definitely is. But in sport mode the modern turbos overfuel stars big time to improve response. Of course you can advance right back too with electronic control.
Old 04-02-2010, 11:21 AM
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So am I reading correctly that I should set to 26 BTDC and I can unplug the pot?
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Mark 1979 930 Euro ***GONE AND DON'T MISS IT AT ALL***

"Worrying about depreciation on your car and keeping mileage down is like not ****ing your girlfriend so her next boyfriend finds her more appealing"
--clutch-monkey
Old 04-02-2010, 11:35 AM
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Quote:
Originally Posted by RarlyL8 View Post
This board gets more like Rennlist every day. I apologize Mark for my part in destroying his thread.
Why would you say that?

Were we just supposed to stop when you declared it closed after sending him a copy of the factory specs?

We have stayed mostly on topic about ignitions. It is not like we started talking about someone's trip, new garage, new lift or such. Many threads get pulled a bit off topic to some degree and evolve. It has not expanded any more than many other threads.

Many of us have benefited I suspect. I know I did and believe that I got and lot out of it and learned the following from our discussion:

I have learned that the single and double connection pot 3.3 distributors have different pot orientations. (push v pull on different sides of the rotation).

I have learned that Porsche calls the 'pot' a 'pressure box'.

Than none of the 3.3 distributors have Vac-Advance. Untill now I thought the singles might.

I have learned to accept that the single pot dist's do not have any 'boost retard'.

I picked up another good data point in that you have been successfully running -26 deg with .75 bar on boost without problems which is a lot more aggressive than I believed possible.

I have come to the conclusion that a euro dist is probably not the best set up for a best practices distributor build as suggested. In fact it looks like it has a major weakness with no boost-retard when most every other performance turbo car built dose.

IMO Mooney should question what his mechanic did. Anyone can make a mistake. Said mod is unorthodox and I highly suspect it dose not function as intended.


Quote:
Originally Posted by RarlyL8 View Post
...When the distributor is modified the difference transforms the driveability. One of the services I would like to offer my clients is distributor tuning, there is a lot to be gained there.
It looks like we agree that there may be great opportunities on the often ignored ignition side. It seems the more we learn about the ignition side the better we can all make decisions about what if any mods might be considered.

If anything Mark might be prod that he started a thread that grew legs and became possibly valuable and substantial. With the number if members tied to in now, any added questions he might have will have a good audience and probably return quick response.

Now it is I that must apologize to all for my rant. Sorry guys.

I think this has developed to one of the better threads of late.
Old 04-02-2010, 11:39 AM
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Quote:
Originally Posted by 911st View Post
Why would you say that?


Now it is I that must apologize to all for my rant. Sorry guys.

I think this has developed to one of the better threads of late.
Really?!
Do you think that this thread, now going on 5 + pages, timely and concise?
This question should have been handled in one page, but it gets into all this supposed "theory" and speculation.

"The guy asked for the time, and this thread tells him how to build a frick'n watch".
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Old 04-02-2010, 11:51 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #92 (permalink)
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Quote:
Originally Posted by equality72521 View Post
So am I reading correctly that I should set to 26 BTDC and I can unplug the pot?
Mark,

I am not an expert on 930 ignitions but am learning all I can about them.

Have you done any tests yet.

What happens when you pull the vac line to the dist at idle? What happens when you set timing and then install or remove the vac line and recheck?

JMO:

From what I have learned so far, the single pots do not seem to have any boost retard.

US distributors do not run any more than about 16 to 20 deg advance on boost.

This puts you in a difficult position as to making a decission. To stay with this dist you will have to run more on boost advance than any US dist seems to.

And /or or you will have to run a lot less on cruse advance than the US dist.

Me, I would source a good two pot dist. Or, add MSD with vac retard function for on boost. MSD and 930's are a great combo anyway.

If I had to run a single I would keep the boost stock (.8 bar), run the best fuel possible and try running closer to -20 but no more than up to -25 timed at 4000rpm with the Vac Retard disconnected. Only if I had to.

This will not be great for idle or cruse. If you pull it back as much as I suspect you should I might leave the Vac-Retard hose off hoping to help idle quality some.

Having said all that. Many seem to just set them at -26 and running them.

From what I think I know, that might be a risky thing to do.

Again, sorry for getting carried away if it bothered you.
Old 04-02-2010, 12:05 PM
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Life is all about choices, and we can choose to wade through the detail ad-nauseum, contribute or not contribute, question and debate eachother's logic, but in the end it's all about learning.

True, a single page response would have sufficed, but it just took awhile for the thoughts to gel. Speedy summarized all that I needed in his one post re: the differences between Euro/Calif. dizzies. The rest I'm smart enough to figure out and apply myself.

In this forum, be prepared to get more than you asked for. It's been fun, let's do it again!
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Old 04-02-2010, 12:39 PM
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Dave,

You just want to get in to it. Lets be honest, you love jumping on this kind of thing and it is not the first time you have called me out.

Your response has a lot less to do with the discussion than anything contributed so far and can only have the effect to derail a good thread!

This is a social form.

No one owns any threads they start or participate in.

Hopefully we can get back to distributors and vac pots and yes, even helping Mark.

Last edited by 911st; 04-02-2010 at 12:59 PM..
Old 04-02-2010, 12:56 PM
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Keith,
You want to make this public, you got it.
What I'm "calling you out on" is going off topic. If there was an award for it, you'd own it.

"Hopefully we can get back to distributors and vac pots and yes, even helping Mark."

I see you have set the order of precedence, by maybe "even helping Mark". Congratulations for taking over yet another thread.

Mark, my apologies.

On the subject of the distributor, please get the thing checked out. It's over twenty years old and who knows when it was last checked out mechanically. Porsche distributors are notorious for gumming up in the advance mechanism and not working properly or not at all.
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Old 04-02-2010, 01:29 PM
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Last edited by 911st; 04-02-2010 at 02:13 PM..
Old 04-02-2010, 02:01 PM
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Original post:

Quote:
Originally Posted by equality72521 View Post
I've searched but I'm still confused. I have a euro single pot distributor that I understand to be vacuum retard at idle/low rpm and mechanical advance above 4000 rpm. Does this pot have any other use throughout the rpm range? Does it serve any other purpose on a turbo engine? Is there an advantage/disadvantage to disconnecting it?
No, no, no.

Original question answered.

Isn't that a lot more fun!
Old 04-02-2010, 02:14 PM
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Quote:
Originally Posted by equality72521 View Post
I'm confused. The factory manual clearly states, in no uncertain terms, that idle for R.O.W. cars is to be set at 29 BTDC @4000RPM with vacuum hose disconnected.


Directly from the manual:


ADJUSTING IGNITION TIMING FROM 1978 MODELS


Adjusting Values:
Europe. R.o.W.
29 before TDC at 4000 rpm

Europe version requires the detachment of vacuum
hose at distributor. It remains connected for USA,
California and Japan versions.
In my eyes, there is a little translation fault:

In the German manual it says to adjust to 0 at idle with hose connected, then check at 4000 rpm and it should be 29. if not, somethings wrong with the distibutor
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Old 04-03-2010, 02:10 AM
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Quote:
Originally Posted by proffighter View Post
In my eyes, there is a little translation fault:

In the German manual it says to adjust to 0 at idle with hose connected, then check at 4000 rpm and it should be 29. if not, somethings wrong with the distibutor
In the factory manual I have it has two measurements. One is Ignition Timing and the other is Ignition Timing Control.

Ignition Timing is set to 26 BTDC @ 4000 RPM with engine oil @ 80C

Ignition Timing Control is checked at 0 +- 3 @ idle speed of 950 +- 50 RPM (vacuum hose connected). It also specifically notes before proceeding to check Ignition Timing Control to set Ignition Timing correctly.

This would indicate that the Ignition Timing is set first to 26 BTDC with vacuum hose disconnected, THEN check correct Ingition Timing Control (pressure pot control) with vacuum hose connected. Not the other way around.
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--clutch-monkey

Last edited by equality72521; 04-03-2010 at 06:33 AM..
Old 04-03-2010, 04:10 AM
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