Wanna start a GOOD discussion....
11-05-2001, 06:06 PM
#1
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Wanna start a GOOD discussion....
It stems from cmh's post...
https://forums.audiworld.com/performance/msgs/37542.phtml
I don't want to argue tuners and what they do and not do. What I want to discuss is timing. When is there too much timing? What are limits under what conditions, and what systems are in place to pull back things to a safe limit? From what I understand the ECU can only pull back 15 degrees of timing based on data from the knock sensors.
WHat is an acceptable level of timing that won't damage things.
Line up the soapboxes.
https://forums.audiworld.com/performance/msgs/37542.phtml
I don't want to argue tuners and what they do and not do. What I want to discuss is timing. When is there too much timing? What are limits under what conditions, and what systems are in place to pull back things to a safe limit? From what I understand the ECU can only pull back 15 degrees of timing based on data from the knock sensors.
WHat is an acceptable level of timing that won't damage things.
Line up the soapboxes.
11-06-2001, 12:18 AM
#3
The best timing is one that will have the largest pressure from the expanding ignited mixture at...
15 ATDC (yes after when the piston is ready to apply torque on the crank - moving downward)
What number is that? I have no idea
Reason? So many thing affect the timing requirement. Let me brainstorm a few...
flame speed - This is the speed at which the mixture ignites. Can vary from say 50 feet per second to over 150 fps. What affects this?
- leaner mixture = slower flame speed - look at an A/F ratio vs power. You'll see that on the leaner side past lambda, the power drops off significantly. Richer mixtures burn faster, but eventually too rich will have a slower flame speed also
- compression ratio - or the pressure of the mixture. Forced induction effectively increases compression ratio which makes the mixture burn faster
- density - related to air/fuel, compression ratio and air temp. The denser the mixture, the faster the flame speed
- turbulence - in the combustion chamber design - since fuel is atomized and not a gas, some turbulence is required in the chamber (no wonder tornado is in business) but this is already factored in most well designed engines. Turbulence causes the air fuel to be well mixed - or something like that
Ok back to ignition timing, what others affect it? well
Octane used - higher octane as we all know resists ignition must be ignited sooner. But what requires higher octane? Ok, another list to brainstorm....
compression ratio, the higher, the more tendency to pre-ignite, so a higher octane will help avoid that.
hot spots in the chamber will ignite the mixture, higher octane will help combat that
Higher air temps help cause pre ignition also. Need higher octane.
A/F ratio again. Leaner needs higher octane to help avoid detonation and preignition.
Back to timing again. This is getting messy.
RPM. At 6000 rpm, TDC comes in 6 times faster than at 1000 rpm (duh so a 5 BTDC timing will need to be around 30 BTDC at 6000 rpm to allow ample time for the mixture to ignite
Using cams with little overlap? Good for high rpm but at idle or low rpm, some of that exhaust gas probably is still sitting there, so a richer mixture is required and more timing to ignite this slow burning setup earlier.
I'm missing a few more things but time for bed now. I'll think of some more on my lunch tomorrow
But bottom line, it's pretty hard to determine. Manufactures spend months to dyno their engines and create maps, then drive it around with various condition and loading to create more maps.
As you pointed out, the knock sensors - along with air temp and coolant temp help fine tune timing back down. Ok, that's all for now
What number is that? I have no idea
Reason? So many thing affect the timing requirement. Let me brainstorm a few...
flame speed - This is the speed at which the mixture ignites. Can vary from say 50 feet per second to over 150 fps. What affects this?
- leaner mixture = slower flame speed - look at an A/F ratio vs power. You'll see that on the leaner side past lambda, the power drops off significantly. Richer mixtures burn faster, but eventually too rich will have a slower flame speed also
- compression ratio - or the pressure of the mixture. Forced induction effectively increases compression ratio which makes the mixture burn faster
- density - related to air/fuel, compression ratio and air temp. The denser the mixture, the faster the flame speed
- turbulence - in the combustion chamber design - since fuel is atomized and not a gas, some turbulence is required in the chamber (no wonder tornado is in business) but this is already factored in most well designed engines. Turbulence causes the air fuel to be well mixed - or something like that
Ok back to ignition timing, what others affect it? well
Octane used - higher octane as we all know resists ignition must be ignited sooner. But what requires higher octane? Ok, another list to brainstorm....
compression ratio, the higher, the more tendency to pre-ignite, so a higher octane will help avoid that.
hot spots in the chamber will ignite the mixture, higher octane will help combat that
Higher air temps help cause pre ignition also. Need higher octane.
A/F ratio again. Leaner needs higher octane to help avoid detonation and preignition.
Back to timing again. This is getting messy.
RPM. At 6000 rpm, TDC comes in 6 times faster than at 1000 rpm (duh
so a 5 BTDC timing will need to be around 30 BTDC at 6000 rpm to allow ample time for the mixture to igniteUsing cams with little overlap? Good for high rpm but at idle or low rpm, some of that exhaust gas probably is still sitting there, so a richer mixture is required and more timing to ignite this slow burning setup earlier.
I'm missing a few more things but time for bed now. I'll think of some more on my lunch tomorrow
But bottom line, it's pretty hard to determine. Manufactures spend months to dyno their engines and create maps, then drive it around with various condition and loading to create more maps.
As you pointed out, the knock sensors - along with air temp and coolant temp help fine tune timing back down. Ok, that's all for now
11-06-2001, 12:28 AM
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Adam, drop me an email.
i want to hear more about the problems you had with your densos.... mine have been great, no probs, smooth as when i first installed them. what are you running now?
11-06-2001, 04:26 AM
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As much as you want to run without knocking/detonation(edited)
more is not necessarily better but that doesn't mean you don't want to advance it. The only time it's too much is when you make too much torque for the engine internals to handle, but that's a whole other issue of matching turbo with hardware. There is a point where max torque is achieved. IMO there is a fine balance between how much boost you can run and still getting advanced timing. Running too much boost on stock intercooler is a bad thing and any time ECU pulls back timing is usually due to too much spike.
What I have noticed on the 1.8t is that nondbw does not have the boost spike dbw has therefore nondbw runs much more timing and usually has more consistant performance. I wonder if the boost spike could be reduced on a dbw car to run more timing and keep things cooler.
Just for reference, the DSM guys with 16Gs and such runs 17psi and 17degrees of timing to start with and increase boost from there. There are cars that runs high 12s with a turbo simular in size to a T28. Some cars run a ton of boost and the timing goes down to almost nothing. IMO more boost is not always better, keeping the timing should be the priority to ensure an efficient burn.
What I have noticed on the 1.8t is that nondbw does not have the boost spike dbw has therefore nondbw runs much more timing and usually has more consistant performance. I wonder if the boost spike could be reduced on a dbw car to run more timing and keep things cooler.
Just for reference, the DSM guys with 16Gs and such runs 17psi and 17degrees of timing to start with and increase boost from there. There are cars that runs high 12s with a turbo simular in size to a T28. Some cars run a ton of boost and the timing goes down to almost nothing. IMO more boost is not always better, keeping the timing should be the priority to ensure an efficient burn.
11-06-2001, 08:08 AM
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Here's what I know, and some datalogging I did a while back....
Usually the ECU will retard the timing before knock has a chance to occur, instead of relying on just a knock sensor. That way the knock sensor is used as a fail-safe. Ideally, you want to run as much as you can, without knocking. In order for the knock sensors to start removing timing, the car has to knock first. This can cause damage over time.
Things like boost, air temp, RPM, load, etc (even coolant temp), can cause changes to the ignition timing. If you look at the graphs below, the intake temp dropped 40 degrees, and the timing dropped accordingly.
The ECU will dial in as much timing as it thinks it can get away with using the current operating parameters, then rely on the knock sensor to adjust if it goes too far.
The knock sensor retarding 15 degrees is PLENTY, unless there is something majorly wrong with the car (burning oil for example), or the chip tuner is way too aggressive.
Usually, you can run more timing off-boost. If you look at the graphs, at the RPM points where boost starts to drop off, timing advances.
With my XR4Ti, the base timing was adjustable. By advancing it, off-idle power was great, but would detonate with boost. Retarding it, low-end power suffered, but top-end power increased (no detonation). I now have an EEC-Tuner, so I can adjust the timing tables to whatever I want (they use load vs. RPM to get a timing value)
So, ideally, you want more timing off-idle, that decreases with boost.
There is a point in which more timing will cause a loss of power, but most cars will never get to that point because of detonation.
Every car is different. Chip manufacturers can't get too aggressive because there is a good chance that what works on one car, is too much for another. A chip is a good start, but some dyno-tuning would be able to get even more power.
Runs 1 and 2 without water injection, about 12-14 degrees of timing advance.
<img src="http://pictureposter.audiworld.com/12130/run1.jpg">
<img src="http://pictureposter.audiworld.com/12130/run2.jpg">
Runs 3 and 4 with water injection, about 18-19 degrees of timing (yes, that's a missed shift in run3)
<img src="http://pictureposter.audiworld.com/12130/run3.jpg">
<img src="http://pictureposter.audiworld.com/12130/run4.jpg">
Things like boost, air temp, RPM, load, etc (even coolant temp), can cause changes to the ignition timing. If you look at the graphs below, the intake temp dropped 40 degrees, and the timing dropped accordingly.
The ECU will dial in as much timing as it thinks it can get away with using the current operating parameters, then rely on the knock sensor to adjust if it goes too far.
The knock sensor retarding 15 degrees is PLENTY, unless there is something majorly wrong with the car (burning oil for example), or the chip tuner is way too aggressive.
Usually, you can run more timing off-boost. If you look at the graphs, at the RPM points where boost starts to drop off, timing advances.
With my XR4Ti, the base timing was adjustable. By advancing it, off-idle power was great, but would detonate with boost. Retarding it, low-end power suffered, but top-end power increased (no detonation). I now have an EEC-Tuner, so I can adjust the timing tables to whatever I want (they use load vs. RPM to get a timing value)
So, ideally, you want more timing off-idle, that decreases with boost.
There is a point in which more timing will cause a loss of power, but most cars will never get to that point because of detonation.
Every car is different. Chip manufacturers can't get too aggressive because there is a good chance that what works on one car, is too much for another. A chip is a good start, but some dyno-tuning would be able to get even more power.
Runs 1 and 2 without water injection, about 12-14 degrees of timing advance.
<img src="http://pictureposter.audiworld.com/12130/run1.jpg">
<img src="http://pictureposter.audiworld.com/12130/run2.jpg">
Runs 3 and 4 with water injection, about 18-19 degrees of timing (yes, that's a missed shift in run3)
<img src="http://pictureposter.audiworld.com/12130/run3.jpg">
<img src="http://pictureposter.audiworld.com/12130/run4.jpg">
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11-06-2001, 08:13 AM
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My goal has always been ~18 degrees of advance...
...anything above this and you need to run race fuel. I had such a chip that would run up to 22 degrees of advance but the ECU would always pull it back. It also got to the point where I could actually hear one or two pings and then you could feel the car stepping back and forth on the timing to ride the knock sensor (not good for the valves BTW).
Mike O.
Mike O.
