Mark,

That info is in this thread early on I believe. I know we have the vac advance curve and I think we have the mechanical advance curve. They just need to be layered against the base timing spec.

From memory I think with a stock car we start at about +1 at idle, instantly go to about - 7 with loss of vac, we then have about 18 deg of mechanical advance that comes in on top of that in a linear manner and is full in by about 3000rpm putting us at about -26. Boost retard is about 8 deg and pulls us back to about -16. I forget when full retard comes in by but I thing it is in the post somewhere as Chris figured this out on a Sun dist system. I believe it only takes about 5 ps to get full boost retard. I am thinking that is a bit fast and is limited by the amount of spring pressure that can be used for vac-retard. Having a boost signal to both sides of the pot might slow that down but we know it should be fully retarded by about .7 bar.

I know this thread has a lot of extra stuff in it but I think this basic part is in the first page or two and repeated throughout. I could be wrong.

You're correct on all that, except maybe the 5 psi for full boost retard. All this info is floating around in my head from zillions of posts, and it guides me to make the right tuning decisions. Personally, I don't feel that a little extra timing is going to hurt early to mid boost, provided we end up with relatively stock numbers when full on the rocket ship with the afterburners glowing.

Keith,

I pretty much concur with your last couple of posts. While going through all this I have tried to practice due diligence in arriving at what I feel is the optimum timing I'm going to run. I have taken into consideration the specific mods I have and feel safe with my conclusion.


To hedge my bet I have personally spoken to four of, what I consider, the best 930 tuners in the USA. The interesting thing about this is that the four opinions are within 4* of each other on max advance at 4000 RPM and 1 BAR of boost.

All four gave the same 4 prerequisites before offering an opinion on timing.

1. Fuel system condition: proper system and control pressures, injector flow
and pattern even, and fuel pumps pressure in spec., and most
importantly "Premium Fuel Only"

2. Larger intercooler ie. factory C2 or quality aftermarket

3. Free flow exhaust system

4. Fuel head modification, adjustable WUR, DWUR or any other form of
fueling increase that can consistently maintain afr's under load
between 12.3 and 11.5

On the subject of timing all 4 recommended

10*- 20*BTDC of initial timing at idle.
(Either block off vacuum advance/retard and set initial timing at 10*- 20*BDC or leave vacuum advance/retard connected and add sufficent timing to get the
10*- 20*BTDC off idle)

26* BTDC (US & CA) 29* BTDC (ROW)
(No load 4000 RPM Vacuum Connected)


16*- 20* BTDC at 4000 RPM and 1 Bar of Boost



If you look at the opinion of the experts we were pretty well on target with this thread. The one thing I may have exception with is following BA's suggested timing recomendation. When Bruce wrote the book there was no way to control afr's and that ability alone makes a drastic difference. I'm presently reading through the documentation for my new model DWUR and this thing is amazing. You have the ability to set control pressure every 250RPM based on RPM and MAP. You now have the ability to program out all
the rich or lean condition that drove 930 owners nuts with the original non adjustable CIS. This advance alone will make lean condition detonation a thing of the past.


Cole

cole, thank you. thats good info for us EFI and you cavemen ;) dizzy folk. I love this thread

dr,

That exactly what Wayne intended this forum to do. All of this thread is a result
of hashing and rehashing, opinions and exceptions from a lot of good people and good friends. Ya gotta love these bums. AIN"T AMERICA GREAT !!!!!!!

Cole

J,

Been meaning to let you know. MSD sells timing tape in packs of 8 you can find it on Evilbay runs about $4.00 covers pully dia. up to 8".

Cole

Nice summary, Cole. The timing you mention above relates to single-plug engines, yes? Twin-plugging advance? (subtract an additional 5-8* @4000RPM/1 BAR Boost?)

Dave,

Sorry I hadn't clarified that earlier. I directed all my research and posts toward
us Smucks that can only afford bolt ons, and usually, one at a time. My car has been a 7 year modification project that started with a written list and 3 stipulations.

My stipulations were: 1. I had to finish designing and building my wife a new house. ( My wife happens to be the sweetest soul God ever put on earth and I most certainly do not deserve her. ) 2. No mods that require engine disassembly. 3. Everything done had to be paid for with disposable income. ( I cheated a little when I tried to convince my Insurance Co. that my DWUR was a new implantable chemo pump )

My wife's house is done after 5 years on nights an weekends ( It is known, in this small ultra conservative Indiana community, as ("The Weird House")

The "Old Sled" is on track for it's tire smoking debut on my birthday Mar. 17

For all reading this: I would like to further promote the listing of your cars specs in your signature. I have found it very informative in doing comparisons when considering further modifications and I think others will also.


Cole

When you take the boost out of the equation, notice how similar Cole's timing numbers are to a modern performance small-block Chevy:


Ignition Timing for Better Fuel Economy - Strategies & Techniques - Rod and Custom Magazine

Dave,

You mention pulling timing back 5-8 deg with twin plugs.

That seems to about right on a normal aspirated motor. For reference a 3.2 at 5000rpm seems to be -18 to -24, a higher compression 3.6 with knock sensing seems to be about -15. From personal experance my 2.4S at 9.2 CR I ran about -33 deg total advance. On my 2.8 Twin plug w 10.4/CR I ran about -25.

However, under boost on a 930 the timing may not be different at all between a single and twin plug from what I think I have been seeing.

I suspect this might have something to do with the more open chamber design of a 930 that dose not put a high piston dome so much in the path of flame propagation and the high effective compression achieved under boost that accelerates the combustion process.

Pre boost is a different story. Twin plugs offer a solid advantage on a 930 by increasing pre boost TQ up to 5%. Further they can make for better assurance of proper combustion of a mix that can be difficult to fire because of the poor AFR's (lean) that can come with CIS combined with very low effective compression that is exaggerated almost one point lower with sport cams.

I find it interesting that RUF did not twin plug there Yellow Bird nore did Porsche there 993TT which were both pretty much open budget cars. However, Porsche twinpluged all there 3.6 high compression air cooled cars.

Mark,

We were talking about advance on boost. Another approach. Euro timing is -29 deg at full advance, US is -26 at full advance to accommodate fuel differences. Boost retard is 8 to 10 deg per Chris's test on dist machine and the factory curve posted early in this thread.

Thus, full boost timing from the factory seems to have ranged from -16 to -21. I guess we would have to think this is conservative settings to allow for variations in tune and environmental factors that can not be compensated for with CIS and mechanical distributor. Euro 930's w stock Intercooers and mostly in-efficient turbos by today's standards that were spec'd up to .85 bar boost.

A stock 930 on a summer day running 1 bar may be in trouble at -14 on boost, a well built turbo on good fuel ruining .8 bar on a cool day with cams might be happy with more than -21 deg advance. I guess it depends?

http://forums.pelicanparts.com/suppo...leys/pint1.gif

Porsche twin-plugged all their racing engines (NA&turbocharged) when ever the rules permitted. Because the 911 plugs are not centrally located with the combustion chamber, flame propagation starts from side of the combustion and travels to the other side. Twin-plugging provides more complete combustion with better control over the release of energy over time, lessens the likelihood of pre-combustion under high boost conditions (1.0Bar and higher), crisper throttle response, and requires less ignition advance. I know of no engine builder that doesn't recommend twin-plugging Porsche turbo engines with bores 97mm and larger.
I believe Ruf and Porsche did not twin-plug because their budgets were not open-ended. Twin-plugging would have required more finances in developing ignition systems completely different than the NA engines. Their decision was budget-based, not performance based. In other words, "bang-for-the-buck".
My $0.02

Keith,

Again I want to reintegrate my comments previous regarding afr control that never existed before. I think we are just now going to see what is capable with CIS because of these advances. Consequently much of what we have been discussing here is, although perfectly valid in the past, may not be totally applicable in the near future. If you look at the ability to change control pressure on the fly every 250 RPM past perceptions change quickly. Bruce Anderson's comments about increasing boost were very valid in there time but I feel this new technology may significantly change what can be done.

Dr referred to us as Cavemen and I got a real kick out of his comment because I am. And I'm proud of it. I cannot express the passion I have for this 30 year old, 2800 lb., tub I lovingly call the "Old Sled" and I will die with her by my side.
Like everyone here I want to get the most I can out of the old girl and we all know there are better alternatives out there now but no matter what alternatives there are it could never be the same. I am lucky enough to own a automotive Icon that set the benchmark for every Marque that followed and it's truly the original supercar. No matter what is to follow the original Porsche 930 is the one that started it all. I've owned this old girl for 22 years and I still find myself opening the garage door before I go up to bed just to look at her and so I will strive to give her more always knowing she will give more back.
Cole

:) - i did mean it with all due respect to the guys keeping the essense of these machines alive.

And it's great that no matter what our own personal idea of "my dream car" is, we all chose these little monsters. I love my 930 and want to give it every chance to accel (pun intended) in life...

Hello !:)

I am happy to share with you the measurement I made on my C2T with it EZ69 ignition...

I installed an USB scope to my mini PC . For this measurement I connected the flywheel trigger on 1st channel and the ignition coil input on the 2nd channel.

Thus I was able to measure the time delay and calculate the ignition advance.
( the reference is given by the idle advance which is equal to 0° ...it has been controled )

here is the recorded data during a 3rd gear pull

http://img20.imageshack.us/img20/672...tionavance.jpg


Then, here is the advance curve

http://img188.imageshack.us/img188/2...ureavance1.jpg


The ignition timing is about 25 - 24° under boost. The ouput of the EZ69 is totally stable as soon as the boost pressure reach or exceed 0.6 bar .

There is absolutely no knock on my engine (verified by sensor) and I run about 1.2 bar (with SC cams), AFR 12.5 at the TQ peak .( 60mkg)


Don't you think that your suggested ignition timing under boost ( I read somewhere 16° under boost ) is too much conservative ?

You got skills my friend!

12.5/1 AFR, 1.2 bar, 25deg advance, wow?

That is more advance than any modern factory air cooled normally aspirated 911 seems to be running under WOT including the 993, 964, and 3.2 Carrera. Also the AFR is leaner than most the air cooled turbo experts are recommending on an even an EFI 930 turbo at those boost levels.

Still, very cool and a good data point for pushing the envelope.

I, too, suggested that 16 is quite conservative a few post back. I run 25 under full boost and the engine just loves it. I'm only running .8 bar right now and it is scary fast. I ran this same timing before I went "slippery slope" with my motor and there was not any physical signs of detonation: no pitted pistons, no broken rings, nothing.

Well, I've been called worse than a dizzy caveman in my life! It's cool; I consider myself a purist at heart (with a twist...or is that twisted?)

You seem perplex...:)

As to the advance , the porsche workshop book is mentioning 21° +/- 3° if the EZ 69 is triggered with 1.75 bar of absolute pressure ....so a 24° degree is in the normal tolerance range. ( and my measurement can also include some tolerance) And as mentionned previously ,if installed, the FVD plate bring 6° more and doesn't bring any detonation or knock under 1 bar with opened ports & 964 C2 cams !!! You don't want to believe but that's a real thing !

As the AFR, for track and very hard conditions, it would be better to drop it arround 11.8 or less. But for road use , sincerely it is too rich for stock or midly modified C2T car. Do you ever make an inspection of the spark plug with a 11.8 averaged AFR ( As I ran during 8000 km) ? Do you think it is a good thing to adjust an AFR to 11.8 at high RPM while the intake/cam/ turbo are out of breath ( but measured boost pressure is still at 1b ) ? Have you connected a device to check under which real parameters (into a given setup) the knock occurs ...?;)

Good stuff, Thierry. Unfortunately I haven't a clue on the differences for a C2T vs. my '87 930. I would be very reluctant to run 25 degrees advance on my car at 1.0 bar boost. Maybe 18, or on a nice cold winter day and fresh high octane gas maybe 20. I can't believe you're getting away with that timing unless your compression ratio is something like 6:0:1. It's worth thinking about!