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?