Who has advanced their timing for more power?
 

I know that timing can be a compromise between power and detonation. I'm wondering if anyone is running advanced timing (beyond factory spec) to increase power.
I was forced to time my SC "by ear" and drive a few days before getting a timing light on it. It ran good, and did not detonate. Turns out I had it advanced a few degrees. After timing to spec I could notice a drop in power. My car always runs cool and I use 91 octane fuel.
Damage from detonation would be severe. Not worth it? What do you think?

Don

i'm not sure what the factory spec are, however i timed mine on a dyno... w/o a carb tuner there we just advanced timing until the highest lb-ft was reached... and then we ran out of runs...... i do not recal what the timing was set too... however i'm running crankfire ignition (elcctromotive) with twin plugs and 6 coils....

I think this should be retitled "Who has advanced their timing and incurred an $18,000 rebuild?" You mostly can't hear detonation; so you really have no idea (without a sensor) what is going on in your motor. If the factory thought you should try this for better performance, I'm betting they'd have recommended it. I'd say forget it, unless you can add anti-knock sensors so as to know where you are.

check this thread out.....

http://forums.pelicanparts.com/porsche-911-technical-forum/166171-1980-911sc-distributor-recurve-results.html?highlight=timing

Did this about a year ago. Have put on about 10,000 kms including DE's and spirited road runs ( full throttle redline pulls through the gears).

So far no problem. I will do another leakdown test this winter to compare previous numbers.

Cheers.

The dizzy on the 80-83 SC engines has very little mechanical advance. I don't know why but probably has to do with smog. The guys I race with (and myself) run with about 30 degrees total advance at 6000 RPM. This is on stock SC motors with carbs instead of the injection system. Keep in mind this is in race conditions with 91 octane fuel and 9.3 pistons (some of us have 9.8 pistons). You should be very safe if you keep it to 32 or less on your street car.

-Andy

I have advanced my timing incorrectly, initially. I thought the John Walker rec was 38 at 6000 and the car would stutter at 2000-2500 RPM under load. Then JW told me that was too much and rec 35, not 38 and the car runs much better. When the car is colder it stutters at times at the same RPM's, so I am thinking of experimenting with 33 or so and see what happens. But I am maxed out on my adjustment, so to retard it a little more I will have to pull the dist. and move it one tooth over. So I will wait until a free weekend to to that. I have 9.8 Euro spec SC pistons with 92 octane.

I am just an amateur mechanic, but I am not sure how advancing the timing would cause an $18000 rebuild. Aren't you just changing when the spark hits the compressed fuel with respect to the cylinder's cycle. I think moneymanager must be thinking of when you advance or retard the camshaft settings. I did this too earlier, but went exactly to spec (at 1.26mm for 964 cams). But I think I could see how messing with the cam timing could cause you to bang your valves into the cylinder heads (if you didn't do a valve clearance check.)

re-curving the dizzy is different that just increasing the numbers by turning the dizzy.

my stock CIS timing was a horror caused by smog restrictions.



To bad recurving kits are not available like they are for muscle cars.

QUOTE: "I am just an amateur mechanic, but I am not sure how advancing the timing would cause an $18000 rebuild. Aren't you just changing when the spark hits the compressed fuel with respect to the cylinder's cycle. I think moneymanager must be thinking of when you advance or retard the camshaft settings."
_______________

SP2, moneymanager is entirely correct. Over time, detonation can cause holes to be knocked into the tops of your piston(s). That will indeed cause a complete rebuild ($18K or set your own price?).

By advancing the timing TOO FAR in advance, you are causing the mixture to begin to burn WAY BEFORE TDC as the piston is coming up the cylinder.

Set your timing correctly!

I've learned my lesson. I wouldn't try experimenting with advancing the ignition timing again without at least one dyno session to measure the results. Doing it "by ear" or with a timing light is meaningless at best, and very dangerous for your motor. Here's what happened when I did that with an SCCA ITB race car that I had after moving from regular to high octane and advancing the timing a few degrees.

http://forums.pelicanparts.com/uploa...1117137016.jpg

The point is that distributors are really pretty crude timing mechanism from an engine's perspective, and advancing them is an even cruder form of adjustment. You may not hear the engine pinging (especially with our noisy air-cooled engines), and it may not even do it across the entire rev range. But it doesn't take long for detonation to eat up a piston. The above piston was destroyed in about 1.5 weekends, or within 2 hours of running.

If you are going to play around with the timing, the right way to do it is with a mapped ignition system and some dyno time. An acceptable compromise is to play around with the dizzy advance on a dyno to figure out what the engine needs and will take, and then have your dizzy rebuilt to provide the curve that the engine wants. Any advance beyond that will not produce any extra HP, and will drastically shorten the life of your engine.

But hey, it's your money! SmileWavy

Thanks to Mo Gearhead for adding the ugly details!

Oops, and thanks to John too!

"I think this should be retitled "Who has advanced their timing and incurred an $18,000 rebuild?" You mostly can't hear detonation; so you really have no idea (without a sensor) what is going on in your motor. If the factory thought you should try this for better performance, I'm betting they'd have recommended it. I'd say forget it, unless you can add anti-knock sensors so as to know where you are."

Tell that to the 3.2 guys who run their engines (same basic engine as a 3.0 SC with
200 more CCs) at 40-45 degrees. They feel it's no problem and have no concern
about detonation, e.g. "Like, what's that, my car feels stronger with the performance
chip and most Pelican 3.2 guys do it anyway. Like, don't be so negative."

Have to love it!

I don't want to get off topic here but since the above issue was brought up, i'll comment on it.

SP2 is correct that also cam timing should not be messed with, without ensuring you have ample valve clearance. If I had set my DC20/Super C2 cam timing to the advanced spec of 2.4mm (recommended range of 2.2 to 2.4mm) I would have valves that are well below the recommended piston-to-valve (P-V)clearance of 1.5mm intake and 2mm exhaust. In my case I couldn't even set my cams to the recommended range and had to settle on 1.85mm.

Point being, even a stock motor can be running somewhat tight clearances so it's best to be satisfied with a midrange setting. Or else check your P-V clearance before "blindly" making a perceived performance enhancement adjustment.

Why don't your tell us in your infinite wisdom what you know about you know about timing a motor, the physics behind it, and why you think those guys who do those performance chips have it, in your opinion, all wrong?

I think dyno tuning is the only way to go if you want to run advanced timing. I know guys running advanced beyond factory on SCs, and on the dyno you can clearly discern det when it starts to occur. Least those who know what they are listening for can hear it.

I know guys running advanced timing on remapped 3.2s that have put 30k miles on their motors and they are still producing very strong dyno numbers, so if it done right it's not a problem as far as I can see.

http://forums.pelicanparts.com/uploa...1186075503.jpg



Also Grady has written comments about detonation.




ps: it's hard to beat a nice engine monitoring system. Grady has also commented and made suggestions.

Yes, it is certainly possible to damage an engine by advancing the timing too far. It is easy, in fact.

Yes, it is possible to hear detonation. Sure, some detonation is more difficult to hear and noisy engines make it harder but no, Porsche engines are not somehow magically quiet while detonation is going on. You can hear it.

A trusted mechanic friend of mine who has more experience rebuilding 911 engines than I have drinking beer......tries for 35 degrees full advance. Max. If it works, great. Some do. Mine does. In my case, that is about seven degrees beyond Porsche's safe and conservative factory spec (12 degrees BTDC instead of 5). Some cannot handle it. Detonation occurs. Sometimes, the factory setting is used because that particular engine just won't support 35 degrees full advance. Conventional wisdom suggests you advance timing until you sense detonation, and then back it off a couple of degrees. Again, you CAN hear detonation. Porsche engines are not different in this regard. If you back the timing off until it just barely loses the detonation, and then back it off an additional two degrees, you should be okay. Even then just be vigilant for that cracking sound.

And yes, this additional seven degrees of advance makes a substantial difference in how the engine runs and how much power it makes.

Hi:

One should be aware of a phenomenon called "Sub-audible detonation" and these are shock waves that break rings as well as top ring lands.

I cannot count the number of times that we watched the rings fall on the floor during engine disassembly and the customer said they never heard a sound. Some of these people are ex hot-rodders and not rookies in this regard. :)

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.

My best advice to anyone reading this thread is to never,.....EVER,....rely on your ears as "defacto knock-sensors" unless you have deep pockets ($$$$).

I hope this helps,

I tried advancing a little on my SC on my quest to reduce temps... It worked fairly well as far as temps reduction, but anything beyond 4000 rpm I could hear pinging (cute word, pinging, more like a string of firecrackers). I did not like that one bit and went right back to factory settings....

My 2.2L was running 30 degrees advance when I bought my car, and it was really quick. The first thing my mechanic did was dial it back. He KNEW it was running advanced without even timing it.

He looked at the car, said "hi, nice car - is it running advanced timing, I'd dial it back if I were you!" (and then he gave me the same look that your buddy does when you tell him you're dating his sister.)

Needless to say, I am now only 15 degrees at about 5000 RPM. However, a lot of cars that I see no longer have the vacuum advance hooked up - why is that? Does the vacuum advance make any difference?

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.