Timmer

Pinging, Knocking, And Detonating

11 posts in this topic

Pinging, Knocking, and detonation are all words that describe the same phenomenon. I'll just use the term detonation for this post.

 

If the fuel/air mixture is pressurized and/or heated too much, it will explode like a bomb when it is ignited(hence the term detonate). The "ping" noise you hear when this happens is actually a little sonic boom going on inside the combustion chamber. The shockwave from this little sonic boom is obviously not very friendly to the internals of the motor. It also produces much higher combustion temperatures, which is also not good for motor parts.

 

Detonation is a result of too much PRESSURE and/or HEAT of the fuel/air mixture in the combustion chamber.

 

Below is a quick list of the specific things that can cause detonation(from most common to least common):

 

Fuel octane rating too low

The octane rating of fuel is directly related to it's resistance to detonation. The higher the octane, the more resistant it is to detonation. This is why race fuels are usually up toward the 110 octane range. Leaded fuels are also more resistant to detonation. Lead is a fuel additive that is specifically put into fuel to make it more knock resistant. It is not commonly used anymore because of the emissions it produces.

 

Too much ignition timing advance

You want some ignition timing advance to give the fuel/mixture enough time to fully ignite, but if the piston is compressing the fuel/air too much while it is being ignited it will be more prone to detonate. In modern bikes/cars there is a table in the ECU that defines how much ignition timing to run for different operating conditions.

 

Intake air temperature too high(turbocharger/supercharger)

Turbochargers and superchargers cause higher intake air temperatures because they transfer more heat to the air coming into the motor before it gets to the combustion chamber. More heat = detonation. This is why guys install an intercooler with their turbocharger. The intercooler cools the air before it enters the motor.

 

Too much mechanical compression

If you modify your motor to raise the compression ratio you are compressing the fuel/air mixture more. More pressure = detonation.

 

Fuel/Air Mixture excessively lean

Leaner fuel/air mixtures produce higher combustion chamber temperatures. More heat = detonation.

 

So, if you are hearing a little pinging in your motor it is probably due to one or a combination of these things.

 

Any questions on this stuff?

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Is it also true that it can be called "pinking"?

Well maybe not in other parts of the world, but apparently in Australia. :lol:

No idea why it's called that, but I only learnt about that in the last couple of years.

 

Just going back to the topic of fuel octane ratings - a bit of a myth that you can hopefully clear up... does using a higher octane fuel increase performance (power)?

 

I have looked into this briefly myself and found that really it shouldn't make a difference to power - that a higher octane fuel is only needed to control detonation issues? The recommendation that I came across was to save your money and used the minimum recommended octane fuel (mostly 95 for modern sportsbikes? Or my bike at least.) But ask some different people and I bet they'd swear that they get better power from higher octane fuels. It seems to me like there's alot of people using inaccurate and defective 'seat of the pants' dynos. :P

 

I never knew that Japan has 102 octane fuel available as their Premium (Aussie Premium is 98, which is the Japanese 'Regular'). I guess that explains why some places have such an abundance of vehicles with built engines?

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Hey mugget,

 

Excellent question on octane rating! A lot of people think that higher octane fuel will make more horsepower. This is FALSE! There is a common misunderstanding that leads to this thinking.

 

Let's examine 85 octane versus 92 octane. We know that 92 octane is more resistant to knocking than 88 octane, but why? The answer is in the additives that are put in the fuel. The additives that fuel companies put in the fuel to make it more "knock resistant" actually make the fuel burn slower. By making the fuel burn slower(release it's energy slower) it will be less likely to go "kaboom", or detonate, or knock(same thing).

 

For the same engine, and assuming it doesn't knock, you will actually make MORE horsepower with the 85 octane fuel!

 

I know what you are thinking...why do we use 92 octane if 85 makes the best power? If you look at my previous post about the causes of knock, you can kind of see why.

 

Using the 92 octane fuel you can...

1. Run a higher compression ratio. Higher compression ratio = more power. Most engines these days use much higher compression ratios than 20 years ago.

2. Run more ignition timing advance. More ignition timing advance = more time for fuel/air mixture to burn = more power and better fuel economy.

3. Run a turbocharger/supercharger. Most stock vehicles don't have a turbo, but you ABSOLUTELY need to run higher octane fuel if you have one.

4. Run a slightly leaner mixture. Since you can now run more ignition timing advance, you can also run slightly less fuel because you are getting a more complete burn of the fuel/air mixture.

 

The common misunderstanding is that the higher octane fuel is what makes the best power, but in reality the higher octane fuel just allows the engine to be run at a higher state of tune.

 

Make sense?

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More ignition advance is generally good for economy, but not always for power. You want maximum combustion pressure to happen 15-17 degrees after TDC. Too early, and you waste pressure when the piston is basically motionless (or risk having max pressure before TDC, which isn't good) and too late and the available volume have become big enough that pressure drops too rapidly without doing much work. In other words, simply advancing ignition is no guarantee for more power - you could even end up with less.

 

 

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More ignition advance is generally good for economy, but not always for power. You want maximum combustion pressure to happen 15-17 degrees after TDC. Too early, and you waste pressure when the piston is basically motionless (or risk having max pressure before TDC, which isn't good) and too late and the available volume have become big enough that pressure drops too rapidly without doing much work. In other words, simply advancing ignition is no guarantee for more power - you could even end up with less.

 

Yes...there is a "too far" when it comes to ignition timing just like anything else. The result of that would indeed be less power.

 

However, most manufacturers do not flirt with running ignition timing that close to the limit of knocking. They will usually be conservative with the final ignition timing advance they program into the ECU. They do this because they do not want a bike that will have 10's of 1000's of miles(or more) put on it to knock under ANY circumstances. This is where the power is to be had.

 

In the few hundred or so vehicles I have tuned on the dyno and at the track, most of them gained power just by advancing the timing a few degrees in some area of the map.

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I cannot argue with you since I haven't dynod any bike, but it make sense that fixed ignition is set to cope with low grade fuel with the engine working hard under adverse conditions, hence retarded well away from detonation under most situations. BTW; Does most fuel injected bikes run knock sensors these days?

 

As a curiosity, I remember the old Z1 from the mid-70s gave the most power with the ignition retarded several degrees. Not that it counts for much :lol:

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I cannot argue with you since I haven't dynod any bike, but it make sense that fixed ignition is set to cope with low grade fuel with the engine working hard under adverse conditions, hence retarded well away from detonation under most situations. BTW; Does most fuel injected bikes run knock sensors these days?

 

As a curiosity, I remember the old Z1 from the mid-70s gave the most power with the ignition retarded several degrees. Not that it counts for much :lol:

 

Yes...some of the modern bikes are running knock sensors, but not all of them yet. I'm pretty sure the BMW S1000RR's have one.

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Timmer,

 

Good overview, and nicely put (even I could understand it).

 

CF

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Great info, Timmer!

 

The below especially makes sense, never thought about it that way before.

 

For the same engine, and assuming it doesn't knock, you will actually make MORE horsepower with the 85 octane fuel!

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That's awesome guys. Glad I could clear it up a little for you.

 

That was the quick and simple on that stuff, but there are definitely more details.

 

If you guys think of any questions on that stuff just let me know. :D

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When you dyno the bike how you know that it has to much ignition advance and knocking, you hear it? Also since there is a knocking sensor on the BMW is it a safety device for knocking? I know there is an ignition module for the BMW. Did you tune any S1000RR with stock engine? Do you have an example map? With HP calibration kit you can deactivate the knocking sensor which may limit your tune if done correctly.

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