C'mon and knock...

[mach4g63t]

Okay, so, I've beent tryin' to read up on it, but it's not making sense to me. I understand how the Knock Sensor works and how different things can cause the knock sensor to activate and retard timing. But, my question is why/what actually causes knock? It's crank-related right? What happens if your engine fails to correct the knock and what could potentially happen?

Also, I have a 2nd question-- as to eliminate multiple threads. What exactly is the benefit of removing the balancer shaft from the motor?

 

[tkelly27]

http://en.wikipedia.org/wiki/Engine_knocking

Less reciprocating mass. Gives you a few HP and less weight keeping the engine from accelerating.

 

[kenamond]

Okay, so, I've beent tryin' to read up on it, but it's not making sense to me. I understand how the Knock Sensor works and how different things can cause the knock sensor to activate and retard timing. But, my question is why/what actually causes knock? It's crank-related right? What happens if your engine fails to correct the knock and what could potentially happen?

Also, I have a 2nd question-- as to eliminate multiple threads. What exactly is the benefit of removing the balancer shaft from the motor?

The knock sensor listens for pre-ignition and detonation in the cylinders (knock). Knock is bad.

Normally, the spark plug ignites the air/fuel mix at one location. The burn front starts to expand sort of like a growing bubble of fire. This doesn't happen all at once. It takes many degrees of crank rotation for the fuel to fully burn. If you measured the pressure in the combustion chamber, it would start to rise right at ignition and after a bit of a delay for the bubble to really get going it will continue to go up fairly quickly as the bubble grew and then peak out and start dropping back down.

All of that pressure is pushing on the crown of the piston. To get any value out of that, you want the piston to be after top-dead-center so that it's actually helping to turn the crankshaft in the right direction. To get maximum torque, you want this burning to happen just right. All of this is controlled by ignition timing when the fuel/air starts burning.

When the engine is at higher RPM, you actually have to have the spark before TDC so that by the time the pressure is really hitting the roof, you're after TDC. The timing is therefore some crank angle before top dead center. That's your timing advance.

Also, keep in mind that after TDC, the piston is going down the barrel, and the volume above it is getting bigger. Before TDC on the compression stroke, the volume is shrinking. So if you spark earlier, the fuel starts to burn which increases pressure, but the piston is still moving up which also increases pressure due to the shrinking volume above it. So if you advance your timing too much, you might get too high of a pressure as the piston is moving up, and when pressure goes up, temperature does, too. Too much advance can lead to too much pressure which leads to too much heat which can actually detonate the air/fuel mixture. Since the whole air/fuel charge is pretty much at the same temperature when this happens, most of it burns VERY FAST. And this may be before TDC or near TDC. So all that pressure from the big BANG pushes on the crown of the piston, but because it's near TDC, it can't really turn the crank. So you just smack the crap out of your rod bearings (not good). That's pre-ignition.

Now, if you are not quite that bad, but the temperatures are still really high but not enough to pre-ignite, then the spark happens, the bubble starts to grow. This crowds the unburned air/fuel that's outside the bubble. So the unburned air/fuel is being crowded more and more by this growing fire bubble. That crowding is pressure which heats up the unburned air/fuel even more. Since it was already pretty hot, it doesn take much for the unburned stuff to reach a point where it's too crowded and too hot as a result, and BANG it all goes off almost at once. Again, this smacks down on the piston, down the rod, and hammers the rod bearings (not good). That's detonation.

In reality, the location in the combustion chamber where the BANG starts is usually a "hot spot". This could be a sharp corner of a chunk of carbon buildup that's still pretty hot from the last combusion cycle, or it could be a sharp edge on a piece of metal (in the crown). The hotspot is the seed for the BANG which is a much faster growing bubble than the one you actually want. And that bubble again crowds the unburned air/fuel around it (and probably between it and other growing bubbles) and other hotspots can lead to additional detonations. Basically, once it starts, it's going to keep detonating until all the air/fuel is gone.

Now, for turbocharged engines, you can get this from running too high of boost. Higher boost pressure means higher temperatures. If your intercooler can't cool it back down enough (or water/meth injection or whatever), you're closer to knock from the get-go. You'd like to advance the timing just right to get the pressure pushing on the piston at the right time after TDC to maximize torque, but detonation occurs if you do. So you retard the timing (losing torque as a result) but decreasing knock. You do this until knock goes away or is tolerably low. Also, when you boost more, you're cramming more air into the combustion, so when the piston starts compressing it, it gets to higher pressures and temperatures (like jacking up the compression ratio). So that gets the charge hotter and more likely to detonate or pre-ignite. So higher boost means you need to do a better job of cooling it (bigger intercooler, water/meth injection, lower compression ratio pistons) or use higher octane fuel.

The other thing you can do is run higher octane gas. This won't detonate until higher temperature, so you can advance timing more without getting too much knock.

Now, the knock sensor detects knock and retards the timing (delays the spark) based on how much knock it's hearing. There's a simple formula the ECU uses for figuring out how many degrees to retard the timing. I forget the formula, but you can easily find it in a search. So the engine uses the knock sensor so that you don't destroy the motor. But it has to knock to know to retard the timing, so it has to beat up on the motor a bit before it can fix the problem. That's why many tuners tune to knock. Tune your car so that you get just enough knock that it's not a problem and you're about as close to maximum torque as you can get safely.

Hope that helped.

 

[kenamond]

Forgot about the BS issue. The biggest reason folks remove the BS is so that you can get rid of the BS belt. If the BS belt breaks, it often takes out the timing belt with it (gets caught in the timing belt which leads to it snapping). When this happens, the cams stop moving, and valves are left wide open. The piston smacks into the open valves and bends them.

And what tkelly7 said also holds, you reduce the rotational mass of the motor which helps with acceleration. The side affect is more engine vibration.

 

[Zenja]

The knock sensor listens for pre-ignition and detonation in the cylinders (knock). Knock is bad.

Normally, the spark plug ignites the air/fuel mix at one location. The burn front starts to expand sort of like a growing bubble of fire. This doesn't happen all at once. It takes many degrees of crank rotation for the fuel to fully burn. If you measured the pressure in the combustion chamber, it would start to rise right at ignition and after a bit of a delay for the bubble to really get going it will continue to go up fairly quickly as the bubble grew and then peak out and start dropping back down.

All of that pressure is pushing on the crown of the piston. To get any value out of that, you want the piston to be after top-dead-center so that it's actually helping to turn the crankshaft in the right direction. To get maximum torque, you want this burning to happen just right. All of this is controlled by ignition timing when the fuel/air starts burning.

When the engine is at higher RPM, you actually have to have the spark before TDC so that by the time the pressure is really hitting the roof, you're after TDC. The timing is therefore some crank angle before top dead center. That's your timing advance.

Also, keep in mind that after TDC, the piston is going down the barrel, and the volume above it is getting bigger. Before TDC on the compression stroke, the volume is shrinking. So if you spark earlier, the fuel starts to burn which increases pressure, but the piston is still moving up which also increases pressure due to the shrinking volume above it. So if you advance your timing too much, you might get too high of a pressure as the piston is moving up, and when pressure goes up, temperature does, too. Too much advance can lead to too much pressure which leads to too much heat which can actually detonate the air/fuel mixture. Since the whole air/fuel charge is pretty much at the same temperature when this happens, most of it burns VERY FAST. And this may be before TDC or near TDC. So all that pressure from the big BANG pushes on the crown of the piston, but because it's near TDC, it can't really turn the crank. So you just smack the crap out of your rod bearings (not good). That's pre-ignition.

Now, if you are not quite that bad, but the temperatures are still really high but not enough to pre-ignite, then the spark happens, the bubble starts to grow. This crowds the unburned air/fuel that's outside the bubble. So the unburned air/fuel is being crowded more and more by this growing fire bubble. That crowding is pressure which heats up the unburned air/fuel even more. Since it was already pretty hot, it doesn take much for the unburned stuff to reach a point where it's too crowded and too hot as a result, and BANG it all goes off almost at once. Again, this smacks down on the piston, down the rod, and hammers the rod bearings (not good). That's detonation.

In reality, the location in the combustion chamber where the BANG starts is usually a "hot spot". This could be a sharp corner of a chunk of carbon buildup that's still pretty hot from the last combusion cycle, or it could be a sharp edge on a piece of metal (in the crown). The hotspot is the seed for the BANG which is a much faster growing bubble than the one you actually want. And that bubble again crowds the unburned air/fuel around it (and probably between it and other growing bubbles) and other hotspots can lead to additional detonations. Basically, once it starts, it's going to keep detonating until all the air/fuel is gone.

Now, for turbocharged engines, you can get this from running too high of boost. Higher boost pressure means higher temperatures. If your intercooler can't cool it back down enough (or water/meth injection or whatever), you're closer to knock from the get-go. You'd like to advance the timing just right to get the pressure pushing on the piston at the right time after TDC to maximize torque, but detonation occurs if you do. So you retard the timing (losing torque as a result) but decreasing knock. You do this until knock goes away or is tolerably low. Also, when you boost more, you're cramming more air into the combustion, so when the piston starts compressing it, it gets to higher pressures and temperatures (like jacking up the compression ratio). So that gets the charge hotter and more likely to detonate or pre-ignite. So higher boost means you need to do a better job of cooling it (bigger intercooler, water/meth injection, lower compression ratio pistons) or use higher octane fuel.

The other thing you can do is run higher octane gas. This won't detonate until higher temperature, so you can advance timing more without getting too much knock.

Now, the knock sensor detects knock and retards the timing (delays the spark) based on how much knock it's hearing. There's a simple formula the ECU uses for figuring out how many degrees to retard the timing. I forget the formula, but you can easily find it in a search. So the engine uses the knock sensor so that you don't destroy the motor. But it has to knock to know to retard the timing, so it has to beat up on the motor a bit before it can fix the problem. That's why many tuners tune to knock. Tune your car so that you get just enough knock that it's not a problem and you're about as close to maximum torque as you can get safely.

Hope that helped.

Good explanation. I think most people don't really know what knock/pre-ignition is, and it's helpful to understand it, so I like these posts. I think you have pre-ignition wrong though. What you explained there is detonation (knock). Pre-ignition is when the combustion burn starts before the spark happens, so it's a very different thing and has nothing to do with detonation. This could be due to something like a hot spark plug tip, or other hot spots in the combustion chamber. This is most likely to happen when the piston is all the way at the bottom or near the bottom of the combustion stroke. It's very damaging because now the entire combustion is happening all while the piston is making its way up to top, and the pressure from the burn is actually fighting the compression stroke the whole way through rather than contributing to power. The peak pressure happens before TDC. This causes massive heat and is likely to burn holes through pistons, or other such damage. An engine can only tolerate pre-ignition for a very short time before something bad happens.

When people talk about knock, I believe they're talking about detonation. Timing advance shouldn't really affect pre-ignition directly. Here's an excellent (and lengthy) link that explains detonation and pre-ignition. http://www.contactmagazine.com/Issue54/EngineBasics.html

 

[mach4g63t]

That makes sense, and it helps, honestly from an idiot's previous standpoint such as mine. The pre-ignition that was later explained makes more sense too. And while I have a thread going, I was hoping to squeeze a little more knowledge out of you guys... and that is regarding the previous subject of the Balancing Shaft. You said, it's simply less mass the motor has to expend energy to get moving along, but in retrospect it causes the motor to vibrate a little more. The motor vibrates, naturally, as their is combustion taking place. My question is, how much 'extra' vibration does this 'cause and does it work adversely to things like handling? In my mind, a motor that's moving around more than usual would cause some side effects in turns of vehicle handling.

But thanks for all the other info! Big helps!

 

[high klicks]

The balance shaft removed does not create anymore vibration in the motor it just means you may feel more vibration. They just counter act what vibrations may exist in the motor already. How much vibration you feel will vary on each motor based on how well the motor is balanced and each motor's balance is varied based on how well it's put together eg: blueprinted motor should have little to no vibration. When I removed mine I did not notice or feel anymore vibration from the motor. Hope that was helpful

 

[kenamond]

Good explanation. I think most people don't really know what knock/pre-ignition is, and it's helpful to understand it, so I like these posts. I think you have pre-ignition wrong though. What you explained there is detonation (knock). Pre-ignition is when the combustion burn starts before the spark happens, so it's a very different thing and has nothing to do with detonation. This could be due to something like a hot spark plug tip, or other hot spots in the combustion chamber. This is most likely to happen when the piston is all the way at the bottom or near the bottom of the combustion stroke. It's very damaging because now the entire combustion is happening all while the piston is making its way up to top, and the pressure from the burn is actually fighting the compression stroke the whole way through rather than contributing to power. The peak pressure happens before TDC. This causes massive heat and is likely to burn holes through pistons, or other such damage. An engine can only tolerate pre-ignition for a very short time before something bad happens.

When people talk about knock, I believe they're talking about detonation. Timing advance shouldn't really affect pre-ignition directly. Here's an excellent (and lengthy) link that explains detonation and pre-ignition. http://www.contactmagazine.com/Issue54/EngineBasics.html

Good call. I wasn't 100% sober when I wrote that, and I sort of lost my train of thought. I thought I had just described pre-ignition, as you can see in the first sentence after that paragraph ("then the spark happens"). Anyway, I stand corrected.

 

[mach4g63t]

The balance shaft removed does not create anymore vibration in the motor it just means you may feel more vibration. They just counter act what vibrations may exist in the motor already. How much vibration you feel will vary on each motor based on how well the motor is balanced and each motor's balance is varied based on how well it's put together eg: blueprinted motor should have little to no vibration. When I removed mine I did not notice or feel anymore vibration from the motor. Hope that was helpful

I've heard and seen reference to a 'Blueprinted' motor before when looking up performance engines built by different companies. What exactly does that mean? And does it take quite a bit to remove the Balancing Shaft? Where is it located and what tools are needed for it's removal? Does it occupy a space that needs to be filled, or is it as simple as removing a cog or such?