Ignition Timing Thread

[Blackmount]

So I have a few questions, I am searching the Internet for articles, threads, videos etc that can answer my questions and so far I'm having no luck...

My biggest question so far is

Q: If you keep increasing your ignition timing advanced, is there a point you will start loosing power, but no knock will occur?

My understanding the point when it looses power, is when the timing being so advanced it happens too early, and the flame front starts trying to force DOWN the still moving UP Piston; fighting against it. I believe the term they used was "Negative Torque", and this would be described as knock; if no knock is occurring/being registered, is it still a possibility of "Negative Torque" resulting in power loss to happen? I hope I made this clear enough to understand exactly what I am asking.

I am really looking for no guess work but maybe some of our senior members who have some good experience and knowledge on this sort of thing.

edit if changing knock to "Pre-Ignition" helps you understand what I am asking please do so.

[B-Man]

Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

This article talks a bit about Minimum Best Timing and what can happen when you exceed that timing.

Production engines are optimized for the type or grade of fuel that the marketplace desires or offers. Engine designers use the term called MBT ( Minimum spark for Best Torque) for efficiency and maximum power; it is desirable to operate at MBT at all times. For example, let's pick a specific engine operating point, 4000 RPM, WOT, 98 kPa MAP. At that operating point with the engine on the dynamometer and using non-knocking fuel, we adjust the spark advance. There is going to be a point where the power is the greatest. Less spark than that, the power falls off, more spark advance than that, you don't get any additional power.

[Blackmount]

That does not help with the question I was asking though.

Theres a point when power falls off due to too much ignition timing, the ECU SHOULD pick it up as knock, and if its enough retard timing.

Is it possible that you can get to that point where you loose power due to too far advanced timing; but the ecu will not register it as any sort of ping or knock because of it.

Ideally, you can keep increasing timing until knock occurs, then back it off half or a whole degree for optimum power, is that possible.

Your timing makes a huge difference on how much power and how well your engine runs. The whole idea of timing is to make the spark happen just before the piston gets to the top of the compression stroke. You are timing it to a perfect spot for that engine so the piston does not lose and momentum on the way up and gets blown back down with the maximum force possible. If you retard the timing to far, 20 deg BTDC, the explosion happens far before the piston gets to the top and it is trying to force the piston backwards against its stroke. this causes a ping or knock and a loss of power. If you advance your timing to far, 10 deg After TDC, the explosion happens after the piston has reached TDC. This explosion is weaker because the compession has started to lessen in the cylinder as the piston moves down and the momentum has slowed in the engine.

[CoreyB]

Answer is yes

[Blackmount]

Do you have a situation that can support this Corey or are you just mad because I own Chatbox

[DG]

Have you ever tried to shoot a moving target? (or thow a ball to someone who is running?) You can't thow/shoot directly at them, because the ball/projectile takes time to cover the distance between shooter and target, and the target is still moving while the shot is in flight.

Ignition advance is the same thing - it takes some amount of time for the spark to light off the mixture and some amount of time for the flame front to spread through the whole combustion volume and reach peak pressure. So what you are trying to do with advance is light the mixture off early enough to put the pressure peak where you want it relative to the crank stroke so as to maximize the amount of work extracted from that pressure peak.

So the proper amount of advance is contingent on how fast the piston is moving and how fast the fuel burns. Fast piston speed - more advance. Fast burn speed - less advance.

Burn speed is partially determined by the richness/leaness of the fuel mixture, and partially determined by the chemical composition of the fuel itself.

So for a given engine at a given engine RPM, starting at maximum advance and working increasingly retarded, you go:

knock - suboptimal power - optimal power - suboptimal power - burned valves

Burn speed usually correlates highly with octane rating, where high octane numbers translate to slow burn speed. So a high octane fuel may not only allow the use of more ignition advance, but actually demand it. When I ran C16 in the Talon, it really liked a lot of advance.

The big question though is, for a given engine, how large is the window between "knock" and "suboptimal power"? If that window is small, then seeking to ride the knock limit is a legit strategy for maximizing power. If, however, the window is large, attempting to ride the knock limit both exposes the engine to risk and produces suboptimal power.

The only way to know is test.

This is one of the things that continues to baffle me about the import tuner world and has since Day 1: the old school muscle car / NASCAR guys all own engine dynos and play with this stuff in a controlled environment (I once spent a day at Lingenfelter trying a series of harmonic dampers with different elastomers looking for the combination that best damped the crank in our C5 motor) With an engine dyno, you can hold the motor at a specific RPM and then swing the timing back and forth looking for the power peak - it's easy. Import guys have never embraced this and I'm at a loss as to why.

DG

[Greg E]

That does not help with the question I was asking though.

Theres a point when power falls off due to too much ignition timing, the ECU SHOULD pick it up as knock, and if its enough retard timing.

Is it possible that you can get to that point where you loose power due to too far advanced timing; but the ecu will not register it as any sort of ping or knock because of it.

Ideally, you can keep increasing timing until knock occurs, then back it off half or a whole degree for optimum power, is that possible.

On pump gas this tuning method works great because you will usually run out of octane long before you reach MBT.

On race gas and/or ethanol you run into the issue where you can run way more cylinder pressure without knock and ruin the pistons/ bearings. Obviously the closer to the top of the piston travel you fire the plug, the more cylinder pressure will result from the ignition in a smaller space. When this energy starts getting absorbed by the engine instead of pushing the piston back down, you're beyond MBT and thus losing power and killing your motor.

[Greg E]

...and Dennis post was much better written than mine.

[Blackmount]

Have you ever tried to shoot a moving target? (or thow a ball to someone who is running?) You can't thow/shoot directly at them, because the ball/projectile takes time to cover the distance between shooter and target, and the target is still moving while the shot is in flight.

Ignition advance is the same thing - it takes some amount of time for the spark to light off the mixture and some amount of time for the flame front to spread through the whole combustion volume and reach peak pressure. So what you are trying to do with advance is light the mixture off early enough to put the pressure peak where you want it relative to the crank stroke so as to maximize the amount of work extracted from that pressure peak.

So the proper amount of advance is contingent on how fast the piston is moving and how fast the fuel burns. Fast piston speed - more advance. Fast burn speed - less advance.

Burn speed is partially determined by the richness/leaness of the fuel mixture, and partially determined by the chemical composition of the fuel itself.

So for a given engine at a given engine RPM, starting at maximum advance and working increasingly retarded, you go:

knock - suboptimal power - optimal power - suboptimal power - burned valves

Burn speed usually correlates highly with octane rating, where high octane numbers translate to slow burn speed. So a high octane fuel may not only allow the use of more ignition advance, but actually demand it. When I ran C16 in the Talon, it really liked a lot of advance.

The big question though is, for a given engine, how large is the window between "knock" and "suboptimal power"? If that window is small, then seeking to ride the knock limit is a legit strategy for maximizing power. If, however, the window is large, attempting to ride the knock limit both exposes the engine to risk and produces suboptimal power.

The only way to know is test.

This is one of the things that continues to baffle me about the import tuner world and has since Day 1: the old school muscle car / NASCAR guys all own engine dynos and play with this stuff in a controlled environment (I once spent a day at Lingenfelter trying a series of harmonic dampers with different elastomers looking for the combination that best damped the crank in our C5 motor) With an engine dyno, you can hold the motor at a specific RPM and then swing the timing back and forth looking for the power peak - it's easy. Import guys have never embraced this and I'm at a loss as to why.

DG

^ This, I feel the same way, and being forced to be apart of that generation and have to separate the bullshit from facts is a huge headache for me. I try to take a step away from that by spending time on the dyno just to gather info and see what does which and how it reacts to X changes.

However with me living in a new area, and also finances being such a issue for me, it requires alot of waiting time, especially since I have to find a good Dyno Tuner who will let me do or at least do for me what I am wanting to do (should not be a problem if I am paying his/her normal rate for dyno time) also the issue rises finding the same type of dyno, and that the environment is different as those both have effects on dyno numbers and will create alot of naysaying from people when comparing my previous dyno sessions...

Now on the "suboptimal power Window" could you give me a example of maybe a Large Window vs a small/short one? is this something like the space in RPM band this has time to occur in? orrr.....?

On pump gas this tuning method works great because you will usually run out of octane long before you reach MBT.

On race gas and/or ethanol you run into the issue where you can run way more cylinder pressure without knock and ruin the pistons/ bearings. Obviously the closer to the top of the piston travel you fire the plug, the more cylinder pressure will result from the ignition in a smaller space. When this energy starts getting absorbed by the engine instead of pushing the piston back down, you're beyond MBT and thus losing power and killing your motor.

So with that being said, without using a dyno to tune which is obviously preferred:

Should I see if I can keep increasing Timing, until it knocks? I feel like I am already running alot of timing especially compared to how much I was running during my last few dyno runs I did. The car definitely feels great, and is responding well to it; but if there is a safe amount of room for more then I am down to keep going. (I always fill up with 93, never 91, or lower grade fuels if that contributes to the answers I seek) Currently I have it set at 9.5* for the Base Timing, which in my logs is about 34-35 Degrees @ WOT in the high rpm range. (4600-7200rpms)

..and this last portion:

On pump gas this tuning method works great because you will usually run out of octane long before you reach MBT.

On race gas and/or ethanol you run into the issue where you can run way more cylinder pressure without knock and ruin the pistons/ bearings. Obviously the closer to the top of the piston travel you fire the plug, the more cylinder pressure will result from the ignition in a smaller space. When this energy starts getting absorbed by the engine instead of pushing the piston back down, you're beyond MBT and thus losing power and killing your motor.

This was probably the best answer I will get, and almost exactly what I was looking for; which supports my suspicion true that under the right circumstances you can begin to loose power due to too much ignition timing advanced and you will not see the knock from it; it will also potentially lead to engine damage.. (Correct?)

Another "That Being Said": Our engines our pretty tough in stock form as far as the internals go, but from what I have seen on the board the Rings and that area seems to be the weak link, and occasionally the rod bearings...

Obviously too, I am here for advice, and will take it at my own risk. If I go out and run 11* of base timing and blow my engine to pieces; Then, well I will not come back and say it was your fault because blah blah blah. I am above that.

[B-Man]

That does not help with the question I was asking though.

Theres a point when power falls off due to too much ignition timing, the ECU SHOULD pick it up as knock, and if its enough retard timing.

Is it possible that you can get to that point where you loose power due to too far advanced timing; but the ecu will not register it as any sort of ping or knock because of it.

Ideally, you can keep increasing timing until knock occurs, then back it off half or a whole degree for optimum power, is that possible.

The ECU only registers it as knock if it's actually detonation (ie 7 or more detonations detected by the knock sensor)