How do you static-time an SC? On my '66 and '71 with points, it's a simple matter to hook up a test light to the points and turn the distributor so the points open when the Z1 mark lines up with the notch in the fan housing. This is a "basic" static timing of TDC. It gets you in the ballpark so you can start the engine without having any idea of the advance value. How would one replicate that with a reluctor-wheel magnetic pickup?

Making more power by advancing timing is the same flawed logic as making more power by exceeding the rev limit. Can you get away with it? Maybe, for a few seconds until you hear expensive noise. . . this is a point well settled as to be beyond debate in the "centrifugal advance" community. Why it's even debatable when the timing is controlled electronically remains a mystery to me-- I suppose the debate centers around the limit.

"Detonation thresholds in air-cooled engines are NOT static; they change with engine temps (oil and cylinder head), outside air temps, mixture, fuel quality, and load (throttle position & RPM). Further, no two engines are alike, even of the same type. Failure to take all these variables into account when adjusting ignition timing can be an expensive exercise."

"Making more power by advancing timing is the same flawed logic as making more power by exceeding the rev limit."

Both right on!" But spoken "on deaf eyes", as most will never get it.

And that's why Porsche/Bosch used knock sensors beginning with the 964,
i.e. to achieve max performance timing advance and avoid detonation under
ALL engines conditions versus just where the tuner tested for detonation
ignoring all the unknown detonation conditions.

So is your claim that chip tuners are clueless, have have 'deaf eyes', and ignore detonation conditions? That's a pretty broad brush you're painting with. Can you please substantiate that statement with some facts and details and explain to someone clueless like myself why and what exactly these chip guys are doing wrong?

nice explain that I found



"BOUNDARY LAYER and DETONATION

We know that combustion temperatures are in the 3,000ºF to 4,000ºF range. How can this be? 4,000ºF is more than enough to melt steel, so how does the interior lining of the cylinder survive? Why don't we see hotter temperatures on our instruments? Why doesn't the aluminum piston melt down, when aluminum melts at less than 1,000ºF?

There is a "thermal boundary layer," on the order of a millimeter thin or so, that acts as a buffer to protect the steel cylinder walls and the surface of the aluminum piston. The metal and the molecules right next to it will be at roughly the CHT reading or a bit higher, the next layers will be hotter and hotter, until the layer next to the combustion event will be at the combustion temperatures.

That very thin thermal boundary layer acts as a nice insulation barrier, limiting the rate at which heat can be transferred from the bulk combustion gases into the interior walls of the cylinder head, cylinder barrel, and piston. The heat transfer is continuous, as the heat moves first through the boundary layer, and then the cylinder wall and is finally carried away by the cooling airflow around the fins on the cylinders. Each intake stroke brings in a cool new charge, which starts the process all over again. There is also a matter of time of exposure.

The high-pressure part of the combustion event takes up only about 40 degrees or so of crankshaft rotation, and the very hottest part of that only about 20 degrees, so during the other 700 degrees of crank rotation, cooler temperatures prevail. Once detonation becomes serious enough, it disrupts the previously well-organized thermal boundary layer and allows a greatly increased rate of heat transfer from the very hot bulk combustion gases
(up around 4,000F) into the cylinder head and the piston.

This last stage in the process is what starts the damage, and drives the CHTs up."

I think what Loren and others are saying is that without direct 'feedback' (IE knock sensors and the ability to adjust the timing 'on-the-fly') a chip maker is setting a predetermined (static) program into the chip for what is the incremental and final advance.

Relates equally to a vacuum/ centrifugal weight distributor that also has a pre-determined advance rate and final total.

Bottom line is be careful when trying to find H.P. by just bumping your advance
up.

For those interested in the numbers:

www.systemsc.com/tests.htm

Doesn't look good!

Sorry if I don't see it, why doesn't it look good?

Here's a pic of my ignition map. We did quite a bit of dyno tuning in ending up at this. I never experienced detonation (we were wearing Det Cans too) but did runs up and down the range and advanced the timing until it made no more power then backed off a degree. You can see I am all-in at 35 degrees by 4000 rpmhttp://forums.pelicanparts.com/uploa...1186115016.gif

Oh, that's a twin-plugged 3.0 with 11.5:1 CR JE pistons and DR20 cams

If I remember correctly from college, advancing the timing creates a higher pressure spike at the beginning of the combustion process. Total power is the area under the pressure/piston travel curve. Advancing timing quickly generates diminishing power increases in exchange for greatly increased peak cylinder pressures.

Engines will have varying compression ratio, cam timing, state of tune, cylinder deposits, operating conditions & temps, gasoline octane variation, etc. Everything comes with a tolerance. Chances are Porsche set their timing to ensure maximum durability under all possible encountered conditions - a "robust" design.

So, your engine will fall somewhere on a theoretically bell-shaped curve of what ignition advance curve it will tolerate without affecting durability. Stock timing ensures nearly 100% that there will not be timing-caused engine failure. As timing is advanced, more and more engines, more and more of the time, will cross over into causing some damage. If you cross over far enough, or often enough, the accumulated damage eventually becomes "noticeable". I think the SC & Carreras were tuned for 90 or 91 octane, so using 93 octane would provide a bit of cushion.

So my take is, you probably can eke out a few HP and some increases in midrange torque by re-curving the timing. It will even be noticeable the first few times you take the car out. But then it will become status quo, like all other hp increases, and the chance of reducing engine longevity gets bigger. For me, a 4 or 5 % power increase is not worth the chance.

"So my take is, you probably can eke out a few HP and some increases in midrange torque by re-curving the timing. It will even be noticeable the first few times you take the car out. But then it will become status quo, like all other hp increases, and the chance of reducing engine longevity gets bigger. For me, a 4 or 5 % power increase is not worth the chance."

Exactly!

It appears from this thread that only the pre-3.2 911 Porsche owners are the only ones capable
of understanding this. Most/all 3.2 911 owners must have dead brain cells when this topic appears,
as exemplified by the lack posts, or is it that they really don't understand what they're putting
in their cars, i.e. What performance chips really do.

I don't have a stake in this either way but there is one thing I would like to see. If in fact engine longevity is compromised then why is it we are not hearing about it from the masses using them?

I'm not comfortable with being quoted out of context like Loren did so some clarification is needed here.


1) IMHO, there is absolutely, positively no substitute for experience when tuning these engines. Knowing precisely how many degrees of advance these engines will safely tolerate using whatever gasolines, compression ratios, camshaft profiles and displacements must be factored when I setup a distributor in my distributor machine or when mapping Engine Management systems (Motec, for example). It takes experience to know what margins are safe and when an ignition profile is too aggressive for all the variables. Speculation and conjecture based solely on theory is utterly useless in this regime.

2) From experience, Porsche left some large timing margins in some of these cars to accomodate poor gasolines worldwide and with experience, one can safely alter the ignition mapping (advance weights/springs or mapping tables) a bit to make noticable improvements in mid-range throttle response and torque without unintended consequences. In short, there ARE some significant gains to be found with responsible, intelligent changes to advance curves depending on the individual engine. Blanket statements, either positive or negative, are simply inaccurate.

3) Stating wide generalizations about aftermarket chips is just as absurd as making blanket statements focused on race, religion, creed or national origin. Like people, there are good ones and not-so-good ones and tarring everything/everyone with the same brush simply displays incredible ignorance about the subject.


Porsche's family of air-cooled engines vary in design, displacement and ignition mapping tolerances so I'd strongly caution anyone contemplating such changes to discuss such things with experienced and knowledgable personnel intimately familiar with the engine in particular BEFORE making any changes (Steve Wong is one of them). IMHO, this is NOT a DIY'er, "Kentucky Windage" sort of exercise when seeking to make engine improvements with ignition timing alterations unless one can live with the consequences.

No, the pre 3.2 people aren't the only ones capable of understanding this. It's that they have the ability to diddle with the timing very easily and somewhat see the results. Same can't be said for the guys with the 'puters precluding them from going out in the garage and messing with the timing over a beer.

Of course the design engineers for the engine management systems are going to err on the side of caution to ensure the chosen timing spec may avoid detonation under the varying conditions an engine sees throughout it's lifespan. That obviously leaves the door open for some "optimization" and hence the gains by tweaking the chip parameters. And just like everything else in life, it comes at a cost. Nothing's free............

A lot of the Porsche shops here in California tell me you sell performance chips, so instead of buying from these other 'brain dead' chip guys, perhaps we should buy one of yours! How can I get my order to you? Did I hear 'GROUP BUY'?! http://forums.pelicanparts.com/uploa...1186164881.gif

"Porsche left some large timing margins in some of these cars to accomodate poor gasolines worldwide and with experience, one can safely alter the ignition mapping (advance weights/springs or mapping tables) a bit to make noticable improvements in mid-range throttle response and torque without unintended consequences."

And the gasolines 20+ years later are WORSE!

"In short, there ARE some significant gains to be found with responsible, intelligent changes to advance curves depending on the individual engine."

Significant, HARDLY, and only for those that have an interest in selling/hyping group
buys of performance chips, e.g. Rennlist and others. Porsche could have further advanced
the timing in the Club Sport DME, (event racing where high octane fuel would be
recommended and/or used) but kept it the same as the '88/'89 stock DME.

"Porsche's family of air-cooled engines vary in design, displacement and ignition mapping tolerances so I'd strongly caution anyone contemplating such changes to discuss such things with experienced and knowledgable personnel"

Right! And NOT the self-proclaimed ones that profess to be "super engine builders"
who weren't "knowledgeable" until they began reading the hyperbole of the internet,
or those tuners that develop chips using a laptop while driving to tune the engine.

"In short, there ARE some significant gains to be found with responsible, intelligent changes to advance curves depending on the individual engine."

Another one who "doesn't get it", i.e. the point of the thread:

There's a maximum allowable 3.0/3.2 911 timing advance without knock sensors
and as an example it's NOT in the 40+ degree advance area that ALL performance
chips have.

In other words, if we all don't totally agree with Loren then we just don't get it.
Now I understand.
Oh and I guess the have fun salutation must mean it is fun to be an old grouch.:D

In the context of octane, in what way?? California is the only state with sub-acceptable octanes but some engines, notably water-cooled ones, run OK with 91, even with chip tuning. In precise term, tell me WHY they are worse in your opinion?

Thats simply your opinion, sir. I happen to vehemently disagree but you are entitled,...:)

Assuming that you are not referring to me with that slam, might I request some examples of who you "tar & feather"???

Again, assuming that you are not inferring that I fall under the heading of one who "doesn't get it", I think everyone reading this thread understands there are advance limits (without the technical details), but that doesn't preclude making certain changes under controlled circumstances by qualified personnel.

While I respect your right to your opinion on this subject, there are many people such as myself who have invested a lot of resources ($125K+) on engine dynos and various instrumentation/test equipment to learn how these work and allow one to precisely see what happens inside these engines under all kinds of loads and temperatures and therefore have a factual basis for making such changes.

Loren, as I've told you before, I have nothing but the greatest respect for what you do for a living and your work ethic (I've referred people to you) but I think you are truly overreaching when you make such proclaimations about chip tuning and ignition tuning. Until you buy an engine dyno and do some of this for yourself for several years, your credibility in this regard is suspect.

Just MHO, of course,... :)

BOOM!!! HEADSHOT!!!! :D

(the gaming community understands what that means)

Let's see... where's my Funk & Wagnell... H-y-p-o-c-r-i-t-e... hmmmmmm, seems to fit.