hi guys... what are the causes of detonation? other than low octan gas of corse.
MMamdouh
Causes of detonation
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Causes of detonation
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PrecisionBoost
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I deleted prior posts so that I don't confuse people.... I'm going to explain detonation and ignition in depth to give you a better understanding of how things work in a gasoline engine.... and why detonation occurs.
TOP DEAD CENTER = TDC ... the point where the piston is closest to the cylinder head
When the spark plug fires and ignites a compressed air/fuel mixture the process typically takes a while to get going.
Therefore a spark plug will be fired prior to TDC while the piston is still travelling up towards the cylinder head.
This "timing advance" is typically around 10 degrees Before TDC at idle and it can reach as high as 45 degrees Before TDC at high rpm on a naturally aspirated performance vehicle.
The "Flame front" is the area of the air/fuel mixture which is allready starting to expand as it burns.
So at idle the air/fuel is sparked 10 degrees before the piston reaches TDC.... but the flame front doesn't reach the piston until shortly after TDC.
If the flame front hits the piston before it passes TDC it will cause detonation which can destroy connecting rods and pistons instantly.
The burning air/fuel behind the flame front has immense energy ( I can't remember but I think it's around 2000 PSI )
So if that pressure hits the piston as it's coming up the force of the flame front pushing down will be met with the force of the piston being pushed upwards by the connecting rod and crankshaft which is being pushed by the energy generated from the power cycle of the other three cylinders.
Think of it like you would if you were pushing someone on a swing.
The flame front is your hands.... the piston is the person on the swing.
As they come towards you.... you start to put your hands out ( equivilent of the spark plug firing)
Then just as they reach the point where they are closest to you (equiv. TDC).... your hands come in contact with their back and you push them as they accelerate away from you.
Detonation is like putting your hands out too early.... if it's a little bit early it's ok... nothing much happens.... you end up slowing their deceleration towards you a little but you give them a good push as they pass the point that they are the closest to you. ( this is light detonation which most people will call "pinging" or "knocking" )
Ok.... now imagine putting your hands out really early and then you run towards them....... wham........ they slam into you and someone gets hurt.... either they knock you down or the person on the swing falls off.... either way it's a bad situation......... this is the equivilent of full on detonation.
So the key thing is to make sure that your hands contact them just as they pass the closest point to you..... this is the maximum energy transfer you can do.
So in an engine... the spark plug fires and flame front starts before TDC but doesn't reach the surface of the piston until almost exactly TDC.
If the full force of the flame front hits the piston at 0.1 degrees after TDC that would be the absolute perfect situation and you would make massive power.
So.... most manufacutrures will build in several degrees of "retard" to ensure that they don't have problems with detonation.
This is very safe.... it's the equivilent of putting your hands on the back of the person on the swing after they've allready started to move away from you.... the longer you wait the less energy you will be able to transfer to the person on the swing.
As a tuner.... you can advance your timing a little to try and get more power.... but you have to monitor detonation/pinging/knocking.
A tiny little bit of knocking isn't going to hurt anything but all it takes is a change in air/fuel , octane level or heat to change that into a large detonaton problem.
With turbo charged cars you allways have to be carefull to "retard" your ignition several degrees because the air/fuel mixture is very hot and it will take less time for the ignition of the air/fuel to occur after the spark plug has fired.
( for mmamdouh.... I consider the flame front to be "ignition".... most people associate ignition with the spark plug firing )
Your ECU will calculate how early it needs to fire the spark plug to ensure that the flame front hits the piston after TDC.... and it typically uses information from a number of sensor such as the throttle position sensor, air intake temp sensor, map sensor.
If the air temperature is warm... the ECU will move the timing back towards TDC ( for example..... at 3000 RPM with an intake temperature of 50 degrees the ECU might run 35 degrees of advance timing and at 100 degrees it might only run 30 degrees of advance)
Warm air/fuel ignites faster.... so the flame front moves quicker.
If the ECU didn't "retard" the ignition timing by 5 degrees it's possible that the flame front would hit the piston before TDC and cause detonation.
So.... cause #1 of detonation..... intake temperature is too high
Next..... fuel..... if the fuel is a lower octane then the overall air/fuel ratio will increase.
If your ECU was instructing your injectors to fire 30% of the time you might see an air/fuel ratio of 17:1 with crappy gas and 10:1 with race gas.
The leaner the mixture the faster the flame front moves.... so again.... crappy low octane gas will require the ignition to be "retarded" slightly to avoid detonation.
There are also other factors involved..... race gas burns more even than low octane gasoline so it's more predictable and you can tune your ignition very precisely.
In low octane gasoline you might get differences in burn patterns... one small portion of the air/fuel mixture might ingnite faster (flame front moves quicker) which results in a some minor knocking.
Basicly..... heat and air/fuel are really the main two issues that influence spark timing and detonation
Ignition timing has literally thousands of variables so most vehicles will keep the stock ignition timing or use an aftermarket system to modify the original ignition maps.
If you need to completely rebuild your own ignition maps on a standalone system it can take many many hours of tuning on a dyno to get a stable setup.
As I mentioned before..... heat is one thing that causes detonation.... in a diesel engine the heat created during compression is what ignites the diesel.
Because diesel is a slow burning fuel it takes a little while for the flame front to build up pressure and push down on the piston.
If you put gasoline in a diesel truck you would have major problems.... the air/fuel would self ignite well before TDC and cause major pressure on the crankshaft/connecting rod/piston.
In really bad cases a gasoline engine might "self ignite" it's air/fuel ratio before the spark plug fires.... which almost allways results in severe damage to the engine.
This usually occurs when your exhaust temperatures get too high and your pistons get too hot.
This is a major problem in turbo engines..... which is why it's allways a good idea to have a thermal probe in your exhaust manifold so that you can monitor the exhaust temperature.
One way of helping to keep the piston cooler is to keep it nice and clean.... carbon buildup will absorb heat and create a barrier which will decrease heat disipation into the aluminum piston.
Lots of guys will ceramic coat their pistons to ensure that they can tune their car that extra couple of degrees and squeeze out a few more horsepower.
Sorry this is so long..... I hope you get my point..... sorry about the confusion between spark timing and ignition with the previous post.
TOP DEAD CENTER = TDC ... the point where the piston is closest to the cylinder head
When the spark plug fires and ignites a compressed air/fuel mixture the process typically takes a while to get going.
Therefore a spark plug will be fired prior to TDC while the piston is still travelling up towards the cylinder head.
This "timing advance" is typically around 10 degrees Before TDC at idle and it can reach as high as 45 degrees Before TDC at high rpm on a naturally aspirated performance vehicle.
The "Flame front" is the area of the air/fuel mixture which is allready starting to expand as it burns.
So at idle the air/fuel is sparked 10 degrees before the piston reaches TDC.... but the flame front doesn't reach the piston until shortly after TDC.
If the flame front hits the piston before it passes TDC it will cause detonation which can destroy connecting rods and pistons instantly.
The burning air/fuel behind the flame front has immense energy ( I can't remember but I think it's around 2000 PSI )
So if that pressure hits the piston as it's coming up the force of the flame front pushing down will be met with the force of the piston being pushed upwards by the connecting rod and crankshaft which is being pushed by the energy generated from the power cycle of the other three cylinders.
Think of it like you would if you were pushing someone on a swing.
The flame front is your hands.... the piston is the person on the swing.
As they come towards you.... you start to put your hands out ( equivilent of the spark plug firing)
Then just as they reach the point where they are closest to you (equiv. TDC).... your hands come in contact with their back and you push them as they accelerate away from you.
Detonation is like putting your hands out too early.... if it's a little bit early it's ok... nothing much happens.... you end up slowing their deceleration towards you a little but you give them a good push as they pass the point that they are the closest to you. ( this is light detonation which most people will call "pinging" or "knocking" )
Ok.... now imagine putting your hands out really early and then you run towards them....... wham........ they slam into you and someone gets hurt.... either they knock you down or the person on the swing falls off.... either way it's a bad situation......... this is the equivilent of full on detonation.
So the key thing is to make sure that your hands contact them just as they pass the closest point to you..... this is the maximum energy transfer you can do.
So in an engine... the spark plug fires and flame front starts before TDC but doesn't reach the surface of the piston until almost exactly TDC.
If the full force of the flame front hits the piston at 0.1 degrees after TDC that would be the absolute perfect situation and you would make massive power.
So.... most manufacutrures will build in several degrees of "retard" to ensure that they don't have problems with detonation.
This is very safe.... it's the equivilent of putting your hands on the back of the person on the swing after they've allready started to move away from you.... the longer you wait the less energy you will be able to transfer to the person on the swing.
As a tuner.... you can advance your timing a little to try and get more power.... but you have to monitor detonation/pinging/knocking.
A tiny little bit of knocking isn't going to hurt anything but all it takes is a change in air/fuel , octane level or heat to change that into a large detonaton problem.
With turbo charged cars you allways have to be carefull to "retard" your ignition several degrees because the air/fuel mixture is very hot and it will take less time for the ignition of the air/fuel to occur after the spark plug has fired.
( for mmamdouh.... I consider the flame front to be "ignition".... most people associate ignition with the spark plug firing )
Your ECU will calculate how early it needs to fire the spark plug to ensure that the flame front hits the piston after TDC.... and it typically uses information from a number of sensor such as the throttle position sensor, air intake temp sensor, map sensor.
If the air temperature is warm... the ECU will move the timing back towards TDC ( for example..... at 3000 RPM with an intake temperature of 50 degrees the ECU might run 35 degrees of advance timing and at 100 degrees it might only run 30 degrees of advance)
Warm air/fuel ignites faster.... so the flame front moves quicker.
If the ECU didn't "retard" the ignition timing by 5 degrees it's possible that the flame front would hit the piston before TDC and cause detonation.
So.... cause #1 of detonation..... intake temperature is too high
Next..... fuel..... if the fuel is a lower octane then the overall air/fuel ratio will increase.
If your ECU was instructing your injectors to fire 30% of the time you might see an air/fuel ratio of 17:1 with crappy gas and 10:1 with race gas.
The leaner the mixture the faster the flame front moves.... so again.... crappy low octane gas will require the ignition to be "retarded" slightly to avoid detonation.
There are also other factors involved..... race gas burns more even than low octane gasoline so it's more predictable and you can tune your ignition very precisely.
In low octane gasoline you might get differences in burn patterns... one small portion of the air/fuel mixture might ingnite faster (flame front moves quicker) which results in a some minor knocking.
Basicly..... heat and air/fuel are really the main two issues that influence spark timing and detonation
Ignition timing has literally thousands of variables so most vehicles will keep the stock ignition timing or use an aftermarket system to modify the original ignition maps.
If you need to completely rebuild your own ignition maps on a standalone system it can take many many hours of tuning on a dyno to get a stable setup.
As I mentioned before..... heat is one thing that causes detonation.... in a diesel engine the heat created during compression is what ignites the diesel.
Because diesel is a slow burning fuel it takes a little while for the flame front to build up pressure and push down on the piston.
If you put gasoline in a diesel truck you would have major problems.... the air/fuel would self ignite well before TDC and cause major pressure on the crankshaft/connecting rod/piston.
In really bad cases a gasoline engine might "self ignite" it's air/fuel ratio before the spark plug fires.... which almost allways results in severe damage to the engine.
This usually occurs when your exhaust temperatures get too high and your pistons get too hot.
This is a major problem in turbo engines..... which is why it's allways a good idea to have a thermal probe in your exhaust manifold so that you can monitor the exhaust temperature.
One way of helping to keep the piston cooler is to keep it nice and clean.... carbon buildup will absorb heat and create a barrier which will decrease heat disipation into the aluminum piston.
Lots of guys will ceramic coat their pistons to ensure that they can tune their car that extra couple of degrees and squeeze out a few more horsepower.
Sorry this is so long..... I hope you get my point..... sorry about the confusion between spark timing and ignition with the previous post.
Last edited by PrecisionBoost on Sat Nov 05, 2005 10:36 pm, edited 6 times in total.
2010 BMW 335D
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
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PrecisionBoost
- Super Moderator
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- Joined: Thu Jun 19, 2003 5:59 am
- Location: Edmonton, Alberta, Canada
Here is an example of advance timing for a spark plug in a naturally aspirated vehicle... (don't quote me on this.... it's just an example)
800 to 1200 RPM --> 10 Degrees advance
1500 RPM --> 13 degrees advance
2000 RPM --> 19 degrees advance
2500 RPM --> 23 degrees advance
3000 RPM --> 27 degrees advance
3500 RPM --> 32 degrees advance
4000 RPM and above --> 36 degrees advance
800 to 1200 RPM --> 10 Degrees advance
1500 RPM --> 13 degrees advance
2000 RPM --> 19 degrees advance
2500 RPM --> 23 degrees advance
3000 RPM --> 27 degrees advance
3500 RPM --> 32 degrees advance
4000 RPM and above --> 36 degrees advance
2010 BMW 335D
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
this is the most informative post i have ever came accross... thanks for the effort man, i really appreciate it.
now putting that into daewootech terms: is the ignition timing adjustable in our cars? i mean our ECU fires the spark at 10 deg. before TDC... can we do something about that? can a simple OBD scan tool mess with the timing or does that have to be done through modifing the ECU program or so?
the only detonation i am getting on my car is in the bigining of 2nd and 3rd gears while accelerating a bit hard... accelerating easy will not induce that and no other factors affects that issue but the A/C... this is more likly to happen when the A/C is on (the ambient temps are some 35 to 40C at that time) so is that dangerous to the engine? i am using octane 90 on my 1.5 SOHC that got 9.5:1 compression ratio.
MMamdouh
now putting that into daewootech terms: is the ignition timing adjustable in our cars? i mean our ECU fires the spark at 10 deg. before TDC... can we do something about that? can a simple OBD scan tool mess with the timing or does that have to be done through modifing the ECU program or so?
the only detonation i am getting on my car is in the bigining of 2nd and 3rd gears while accelerating a bit hard... accelerating easy will not induce that and no other factors affects that issue but the A/C... this is more likly to happen when the A/C is on (the ambient temps are some 35 to 40C at that time) so is that dangerous to the engine? i am using octane 90 on my 1.5 SOHC that got 9.5:1 compression ratio.
MMamdouh
Driving is the utmost fun you can have with your pants on!
Check out my ride: http://www.cardomain.com/ride/567267
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PrecisionBoost
- Super Moderator
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- Joined: Thu Jun 19, 2003 5:59 am
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If I remember correctly the timing in the Daewoo vehicles is based upon the cam sensor and or crankshaft sensor.
Move either of them and your timing will be out.
Move the position of your cam gear and the timing will also be out.
( which is the only reason Tom hasn't come up with an adjustable cam gear..... the timing is based off the back side of the gear )
The ignition was easy to modify with the older distributor bases cars.... but the new ones are all distributorless so it's not very easy to change timing.
I don't think you can change timing with an OBD scan tool.
Your ECU learns both ignition and fuel maps..... if you are having problems with detonation you should reset your ecu and let it build a new map.
Your engine should also have a knock sensor..... the ECU continuously monitors knock.... if it senses it the engine will usually dump in more fuel and retard the ignition.
Perhaps you knock sensor is malfuctioning and your ECU doesn't realize that it needs to add fuel and or retard the ignition map in that area of the power band.
Like I said before..... a little knock won't hurt things..... but if your feeling it or hearing it that probably means that it's more serious than you think.
If it were me.... I'd locate and replace the knock sensor, reset the ECU and clean out my engine with several applications of fuel injector cleaner.
Move either of them and your timing will be out.
Move the position of your cam gear and the timing will also be out.
( which is the only reason Tom hasn't come up with an adjustable cam gear..... the timing is based off the back side of the gear )
The ignition was easy to modify with the older distributor bases cars.... but the new ones are all distributorless so it's not very easy to change timing.
I don't think you can change timing with an OBD scan tool.
Your ECU learns both ignition and fuel maps..... if you are having problems with detonation you should reset your ecu and let it build a new map.
Your engine should also have a knock sensor..... the ECU continuously monitors knock.... if it senses it the engine will usually dump in more fuel and retard the ignition.
Perhaps you knock sensor is malfuctioning and your ECU doesn't realize that it needs to add fuel and or retard the ignition map in that area of the power band.
Like I said before..... a little knock won't hurt things..... but if your feeling it or hearing it that probably means that it's more serious than you think.
If it were me.... I'd locate and replace the knock sensor, reset the ECU and clean out my engine with several applications of fuel injector cleaner.
2010 BMW 335D
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
where is the knock sensor located on a 1.5 SOHC??
BTW: my car (as well as all Egyptian Lanoses) got no cam position sensor... only a cranck position sensor.
MMamdouh
BTW: my car (as well as all Egyptian Lanoses) got no cam position sensor... only a cranck position sensor.
MMamdouh
Driving is the utmost fun you can have with your pants on!
Check out my ride: http://www.cardomain.com/ride/567267
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PrecisionBoost
- Super Moderator
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- Joined: Thu Jun 19, 2003 5:59 am
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It's usually on the back side of the block somewhere..... I will have to check on my manual.... I'm not at home right now....and we still aren't living there full time (painting, renovations nearly finished)
I will see if I can get over there sometime today and post the location for the knock sensor.
I will see if I can get over there sometime today and post the location for the knock sensor.
2010 BMW 335D
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
that bring us to the question: how does the ECU manage the engine with no CMP?? i don't have one nor does any Lanos in here so how the ECU knows when to fire a spark?
ok the crank position sensor can tell where the crank is but their is 2 crank revs per cycle so how the ECU diffrenciate between the end of a compression stroke (where it suppose to make a spark) and the end of an exhaust stroak 'cause in both setuations the crank will be at the very same position.
i though maybe because our spark plugs fires twice so it doesn't matter but again i found out that this is not true, the first spark is at the end of the compression stroke and the other is at the end of exhaust stroak so with only a crank position sensor it could be mixed up with the exhaust and intake stroaks respectivly.
i know this sounds too confusing but it got to work somehow... my car is a living proof that it does so i have to figure out how it works
MMamdouh
ok the crank position sensor can tell where the crank is but their is 2 crank revs per cycle so how the ECU diffrenciate between the end of a compression stroke (where it suppose to make a spark) and the end of an exhaust stroak 'cause in both setuations the crank will be at the very same position.
i though maybe because our spark plugs fires twice so it doesn't matter but again i found out that this is not true, the first spark is at the end of the compression stroke and the other is at the end of exhaust stroak so with only a crank position sensor it could be mixed up with the exhaust and intake stroaks respectivly.
i know this sounds too confusing but it got to work somehow... my car is a living proof that it does so i have to figure out how it works
MMamdouh
Driving is the utmost fun you can have with your pants on!
Check out my ride: http://www.cardomain.com/ride/567267
Check out my ride: http://www.cardomain.com/ride/567267
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PrecisionBoost
- Super Moderator
- Posts: 4437
- Joined: Thu Jun 19, 2003 5:59 am
- Location: Edmonton, Alberta, Canada
It is a waisted spark system.... that's why you only have two ignition coils.
The spark plugs will fire in both cylinders 1&4 and 2&3 at the same time.
So both spark plugs will fire when #1 is in the compression/power stroke #4 is in the exhaust/intake stroke.
So.... it doesn't matter which one is in which position since both plugs are firing.
Besides being simple... I think the waisted spark system might also help with igniting unburned gasses in the exhaust as they exit the exhaust valve.
I don't know if this is true or not.... I was just thinking that it's a posibility.
The spark plugs will fire in both cylinders 1&4 and 2&3 at the same time.
So both spark plugs will fire when #1 is in the compression/power stroke #4 is in the exhaust/intake stroke.
So.... it doesn't matter which one is in which position since both plugs are firing.
Besides being simple... I think the waisted spark system might also help with igniting unburned gasses in the exhaust as they exit the exhaust valve.
I don't know if this is true or not.... I was just thinking that it's a posibility.
2010 BMW 335D
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
1994 Opel Calibra 4X4 turbo ( C20LET 2.0L Turbo )
2002 Daewoo lanos
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Audacity Racing
- moron
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- Joined: Wed Dec 08, 2004 5:18 am
- Location: Knoxville, Tennessee
- Contact:
i agree with that...
if you have a safc and mess with it a bit on your woo and then you can see fire when you down-shift or even engine brake...
i guess on a stock fuel and intake setup with a sport exhaust you can hear that the is rumble pretty bad (some of you were asking about my exhaust rumble after i let off the accelerator), but with a stock exhaust it get's entirely muffled. i'm shooting 8" flames everytime i downshift or let it engine brake from way high on the rpm scale.
it is a wasted spark
if you have a safc and mess with it a bit on your woo and then you can see fire when you down-shift or even engine brake...
i guess on a stock fuel and intake setup with a sport exhaust you can hear that the is rumble pretty bad (some of you were asking about my exhaust rumble after i let off the accelerator), but with a stock exhaust it get's entirely muffled. i'm shooting 8" flames everytime i downshift or let it engine brake from way high on the rpm scale.
it is a wasted spark
