how is knocking sounding ?
Discussion
Stupid question but I noticed that when further advancing my engine the engine started to sound harsher, albeit the power delivery was quite impressing.
I retarted it now 3 degrees and wonder if this harsher sound is already knocking or just a result of bringing the advancing to the edge. I understand that the stress on the parts is increasing and maybe the sound is a result of this. It seemed that at higher revs the harsh sound was disappearing but in low to mid load situations quite audible.
I retarted it now 3 degrees and wonder if this harsher sound is already knocking or just a result of bringing the advancing to the edge. I understand that the stress on the parts is increasing and maybe the sound is a result of this. It seemed that at higher revs the harsh sound was disappearing but in low to mid load situations quite audible.
Its likely you are experiencing some Knock Ewe but the GM 7 in stock form needs greater protection and has to detect Knock long before its heard by ear.
I dont think you are running GM ecu.... but if your engine is stock internals... ie Flat pistons and GM LS heads (fast burn) then there is no point running much past 26-27 degress of advance on a stock engine from 3000-7000rpm..... have seen this on the dyno, very tiny improvements if any through the whole rev range and not worth it.. the torque goes flat/ backwards with advance.
Just be very careful in testing..... most maps, even the GM stock are set rich at WOT/ high RPM... but you can cause much damage at WOT low-mid rpm, expecially if things are a little hot to begin with. If you do get some serious detonation and it marks the pistons/ head chambers, this only makes the engine more detonation sensitive .. (high-sharp hot spots in the combustion space)
G luck.
I dont think you are running GM ecu.... but if your engine is stock internals... ie Flat pistons and GM LS heads (fast burn) then there is no point running much past 26-27 degress of advance on a stock engine from 3000-7000rpm..... have seen this on the dyno, very tiny improvements if any through the whole rev range and not worth it.. the torque goes flat/ backwards with advance.
Just be very careful in testing..... most maps, even the GM stock are set rich at WOT/ high RPM... but you can cause much damage at WOT low-mid rpm, expecially if things are a little hot to begin with. If you do get some serious detonation and it marks the pistons/ head chambers, this only makes the engine more detonation sensitive .. (high-sharp hot spots in the combustion space)
G luck.
Edited by 738 driver on Friday 13th January 11:24
http://www.youtube.com/watch?v=Due7mkTHMlw
listen carefully about 3 sec into that clip, as the engine suffers from fairly heavy detonation at a mid range rpm. It's the sort of "clicking" or "ticking" sound. As the engine speed increases and moves away from the detonation limit the detonation stops (at around 5 sec in)
As you advance the ignition it is normal to find the engine sounds different. Advancing the ignition angle away from TDC results in a faster rise in cylinder pressure (because more of the charge has burnt before TDC arrives). Generally, assuming that you have not actually advanced into detonation (as in that clip) this makes the engine sound "harder" or "crisper". An excessively retarded engine is often sounding "soft" or "flat" as well.
listen carefully about 3 sec into that clip, as the engine suffers from fairly heavy detonation at a mid range rpm. It's the sort of "clicking" or "ticking" sound. As the engine speed increases and moves away from the detonation limit the detonation stops (at around 5 sec in)
As you advance the ignition it is normal to find the engine sounds different. Advancing the ignition angle away from TDC results in a faster rise in cylinder pressure (because more of the charge has burnt before TDC arrives). Generally, assuming that you have not actually advanced into detonation (as in that clip) this makes the engine sound "harder" or "crisper". An excessively retarded engine is often sounding "soft" or "flat" as well.
Edited by anonymous-user on Friday 13th January 22:30
738 driver said:
Is that advancing the ignition angle 'toward' or away from tdc Max ?.... advance moves it away from tdc, retard is toward or closer I think....
....Intended clarity for the newbies as opposed to nit-picking..
Rgds.
oops, well spotted, now corrected! (was thinkning about optimum burn being closer to TDC in a theoretical sense, but of course you "advance" the timing away from TDC, i.e. you make the point of ignition happen earlier in time, whilst the piston is further down the bore)....Intended clarity for the newbies as opposed to nit-picking..
Rgds.
Mere typo's....
Am working with some top, race two stroke boys at the min (in a general interest-development capacity)... trying to convince them to work on chamber design / ignition advance reduction etc.. Only a minority are on side but they are already getting results...
..... fast burn head/chamber, flatter piston and less ignition advance is the way to economy and performance... less mass in fuel carried etc etc... all good stuff !
Am working with some top, race two stroke boys at the min (in a general interest-development capacity)... trying to convince them to work on chamber design / ignition advance reduction etc.. Only a minority are on side but they are already getting results...
..... fast burn head/chamber, flatter piston and less ignition advance is the way to economy and performance... less mass in fuel carried etc etc... all good stuff !
The knock you can hear without aids ain't that dangerous, the dangerous knock ocure before the hearable knock.
It sounds like this with a headset:
http://www.youtube.com/watch?v=GGJZ6kKzLus&fea...
It sounds like this with a headset:
http://www.youtube.com/watch?v=GGJZ6kKzLus&fea...
harry b said:
The knock you can hear without aids ain't that dangerous, the dangerous knock ocure before the hearable knock.
It sounds like this with a headset:
http://www.youtube.com/watch?v=GGJZ6kKzLus&fea...
Sorry, but that's not the case.It sounds like this with a headset:
http://www.youtube.com/watch?v=GGJZ6kKzLus&fea...
The intensity of the knock, both in terms of the rate of rise of knocking pressure, and it terms of it's duration (crank angle) is directly related to the heat release over that knock event. Hence, the "Louder" the knocking the more greater the potential damage. Every engine has a different threshold for damage and this threshold also is proportional to engine speed (because cycles happen faster).
Typically on an OEM mapped road car engine you would do the following:
<2krpm: limit is set by the knocking pressure that is just inaudible in the passenger cabin. At these low speeds there is sufficient time for any localised hot spots due to knock being quenched before significant damage occurs. Audible "pinking" is a customer quality issue.
>2krpm & < 5krpm: Likely to be the most knock limited engine operation zone, but engine combustion noise will be louder here, so generally the knock will not be as obvious in the passenger cabin as at low speed. Typical engines will be mapped to a 3-5bar knocking pressure in order to achieve maximum torque output. Cylinder specific KCS really helps here because you can retard only the knocking cylinders.
>5.5krpm: The danger zone as engine combustion and mechanical noise will be almost totally obscuring the knocking spectrum. However most road cars engines are not knock limited at high rpm. Most OEMS will have a very low peak knocking pressure limit here to protect the engine (knock can be damaging at this high rpm)
Now for a race car, where you don't care what it sounds like to the driver, you can run the engine into some pretty aggressive knock and still survive. Again this needs to be determined for any given engine. Just because some knock is present does not mean the engine will be damaged. Generally most race engines with a decent KCS will be deliberately run into detonation equally on all cylinders in order to make the highest output.
The problem with the usual aftermarket knock amplifiers are you simply have no idea of the actual knocking pressure for any given "Volume" of knock, and also you have no idea of when it is occuring (in terms of crank angle) and on what cylinders etc.
If you take a highly boosted engine (say a WRC spec one, which is highly knock limited due to the inlet restrictor massively increasing EBP and hence hot in-cylinder residuals) you would find at a cylinder specific crank angle windowed and signal band pass filtered knock system will be able to keep all cylinders at an optimum knocking pressure. A "manual" spark cal could potentially keep the most knock limited cylinder at the same knock intensity but not all of the cylinders. Finally, your manual cal has to be absolutely perfect wrt compensating for any changes in boundary conditions (temps, pressures, fuel quality, sensor drift etc etc) otherwise you risk engine damage because you are flying so close to the knock intensity limit for damage.
(the big issue for many years in WRC however has been reliably sensing knock intensity via an acoustic sensor. In a WRC car there is so much background noise from the transmission (or even gravel hitting the sum!) etc that the signal to noise ratio is very poor.)
Max_Torque said:
Sorry, but that's not the case.
The intensity of the knock, both in terms of the rate of rise of knocking pressure, and it terms of it's duration (crank angle) is directly related to the heat release over that knock event. Hence, the "Louder" the knocking the more greater the potential damage. Every engine has a different threshold for damage and this threshold also is proportional to engine speed (because cycles happen faster).
Typically on an OEM mapped road car engine you would do the following:
<2krpm: limit is set by the knocking pressure that is just inaudible in the passenger cabin. At these low speeds there is sufficient time for any localised hot spots due to knock being quenched before significant damage occurs. Audible "pinking" is a customer quality issue.
>2krpm & < 5krpm: Likely to be the most knock limited engine operation zone, but engine combustion noise will be louder here, so generally the knock will not be as obvious in the passenger cabin as at low speed. Typical engines will be mapped to a 3-5bar knocking pressure in order to achieve maximum torque output. Cylinder specific KCS really helps here because you can retard only the knocking cylinders.
>5.5krpm: The danger zone as engine combustion and mechanical noise will be almost totally obscuring the knocking spectrum. However most road cars engines are not knock limited at high rpm. Most OEMS will have a very low peak knocking pressure limit here to protect the engine (knock can be damaging at this high rpm)
Now for a race car, where you don't care what it sounds like to the driver, you can run the engine into some pretty aggressive knock and still survive. Again this needs to be determined for any given engine. Just because some knock is present does not mean the engine will be damaged. Generally most race engines with a decent KCS will be deliberately run into detonation equally on all cylinders in order to make the highest output.
The problem with the usual aftermarket knock amplifiers are you simply have no idea of the actual knocking pressure for any given "Volume" of knock, and also you have no idea of when it is occuring (in terms of crank angle) and on what cylinders etc.
If you take a highly boosted engine (say a WRC spec one, which is highly knock limited due to the inlet restrictor massively increasing EBP and hence hot in-cylinder residuals) you would find at a cylinder specific crank angle windowed and signal band pass filtered knock system will be able to keep all cylinders at an optimum knocking pressure. A "manual" spark cal could potentially keep the most knock limited cylinder at the same knock intensity but not all of the cylinders. Finally, your manual cal has to be absolutely perfect wrt compensating for any changes in boundary conditions (temps, pressures, fuel quality, sensor drift etc etc) otherwise you risk engine damage because you are flying so close to the knock intensity limit for damage.
(the big issue for many years in WRC however has been reliably sensing knock intensity via an acoustic sensor. In a WRC car there is so much background noise from the transmission (or even gravel hitting the sum!) etc that the signal to noise ratio is very poor.)
Agreed, in fact you say about the same as I tried to explain in one line.The intensity of the knock, both in terms of the rate of rise of knocking pressure, and it terms of it's duration (crank angle) is directly related to the heat release over that knock event. Hence, the "Louder" the knocking the more greater the potential damage. Every engine has a different threshold for damage and this threshold also is proportional to engine speed (because cycles happen faster).
Typically on an OEM mapped road car engine you would do the following:
<2krpm: limit is set by the knocking pressure that is just inaudible in the passenger cabin. At these low speeds there is sufficient time for any localised hot spots due to knock being quenched before significant damage occurs. Audible "pinking" is a customer quality issue.
>2krpm & < 5krpm: Likely to be the most knock limited engine operation zone, but engine combustion noise will be louder here, so generally the knock will not be as obvious in the passenger cabin as at low speed. Typical engines will be mapped to a 3-5bar knocking pressure in order to achieve maximum torque output. Cylinder specific KCS really helps here because you can retard only the knocking cylinders.
>5.5krpm: The danger zone as engine combustion and mechanical noise will be almost totally obscuring the knocking spectrum. However most road cars engines are not knock limited at high rpm. Most OEMS will have a very low peak knocking pressure limit here to protect the engine (knock can be damaging at this high rpm)
Now for a race car, where you don't care what it sounds like to the driver, you can run the engine into some pretty aggressive knock and still survive. Again this needs to be determined for any given engine. Just because some knock is present does not mean the engine will be damaged. Generally most race engines with a decent KCS will be deliberately run into detonation equally on all cylinders in order to make the highest output.
The problem with the usual aftermarket knock amplifiers are you simply have no idea of the actual knocking pressure for any given "Volume" of knock, and also you have no idea of when it is occuring (in terms of crank angle) and on what cylinders etc.
If you take a highly boosted engine (say a WRC spec one, which is highly knock limited due to the inlet restrictor massively increasing EBP and hence hot in-cylinder residuals) you would find at a cylinder specific crank angle windowed and signal band pass filtered knock system will be able to keep all cylinders at an optimum knocking pressure. A "manual" spark cal could potentially keep the most knock limited cylinder at the same knock intensity but not all of the cylinders. Finally, your manual cal has to be absolutely perfect wrt compensating for any changes in boundary conditions (temps, pressures, fuel quality, sensor drift etc etc) otherwise you risk engine damage because you are flying so close to the knock intensity limit for damage.
(the big issue for many years in WRC however has been reliably sensing knock intensity via an acoustic sensor. In a WRC car there is so much background noise from the transmission (or even gravel hitting the sum!) etc that the signal to noise ratio is very poor.)
The most know knock sound recognisable by the non expert is pinking, as you mention the nonaudiable knock is hard do tell from the other engine frequencies, and as mentioned more dangerous at higher enginespeeds.
Offcourse there is audiable destructive knock, but if you hear this the engine is ruined already. Often happens with failing wastegates on turbo engines.
(In the eighties we had this a lot when experimenting with the Renault 5 Tour de corse with turbo pressures up to 2.8bar and very BIG turbos on very small engines)
And to be honest, if it really goes into these details, I met only about 3-4 persons who really knew to identify the knocklimits on higly tuned engines, I'm not one of them.
It should also be noted that generally detonation does not actually kill engines. What happens is audible detonation (explosive sympathetic burning of the air charge at the chamber extremities before the main flame front arrives) causes localise hot spots which lead to inaudible pre-ignition.
This pretty much ignites the fuel as it is injected (effectively it diesels) resulting in massive uncontrolled heat release, which occurs early and hence at large chamber volumes (the piston is still well down the bore). Hence there are no characteristic "knocking" pressure waves to hear. An engine that enters pre-ignition generally overheats it's piston crowns, that then expand excessively, and usually then pick-up on the bore. The added friction from the pick-up finishes things off nicely, adding more heat and leading to a runaway situation when the cylinder will pre-ignite on every compression event as the fuel is added. This continues until the engine siezes, the crown comes off the piston, or typically when the exhaust valve also fails and gets smashed into the piston (burning the charge at low compression ratios (super early burn) means there is little or no expansion availible to cool the post burn charge, this sends EGT's rocketing up, and usually leads to a thermal failure of the exhaust valve.
At this point, most race drivers finally notice and lift off......... ;-)
This pretty much ignites the fuel as it is injected (effectively it diesels) resulting in massive uncontrolled heat release, which occurs early and hence at large chamber volumes (the piston is still well down the bore). Hence there are no characteristic "knocking" pressure waves to hear. An engine that enters pre-ignition generally overheats it's piston crowns, that then expand excessively, and usually then pick-up on the bore. The added friction from the pick-up finishes things off nicely, adding more heat and leading to a runaway situation when the cylinder will pre-ignite on every compression event as the fuel is added. This continues until the engine siezes, the crown comes off the piston, or typically when the exhaust valve also fails and gets smashed into the piston (burning the charge at low compression ratios (super early burn) means there is little or no expansion availible to cool the post burn charge, this sends EGT's rocketing up, and usually leads to a thermal failure of the exhaust valve.
At this point, most race drivers finally notice and lift off......... ;-)
I do know in the Celica days of the WRC the drivers were not happy unless they herd pinking as then they knew the engine mapping was maxed out. But then again the endoscope was stuck up the plug hole every chance they had to check that the engine would last the race. If they saw a perfect condition head on the last stage of the rally they generally added some timing, a good friend of mine was a engine tuner with TTE...
Edited by GTRCLIVE on Sunday 15th January 06:36
But just to remind... the stock LS series are generally large bore N/A, built as light as possible production units.... when not fitted with uprated aftermarket parts the pistons are quite a weak area.... liners too on 7's as they are frequently quite thin in places and do crack at the top (due production inconsistances/tolerances).. getting a 7ltr 520hp 2 valve V8 to return 25-27 mpg and operate flawlessly between 1200 and 7000 rpm has not been done with the most knock resistant components.... tis all relatively light and thinned down in there Gents but works well when combined with the capable GM ECU/EMS.
So despite all the great responses here Uwe do go easy on the road /ear set-up if you are currently running an ECU without knock protection on stock parts...
Good topic and tech replies.
So despite all the great responses here Uwe do go easy on the road /ear set-up if you are currently running an ECU without knock protection on stock parts...
Good topic and tech replies.
GTRCLIVE said:
I do know in the Celica days of the WRC the drivers were not happy unless they herd pinking as then they knew the engine mapping was maxed out. But then again the endoscope was stuck up the plug hole every chance they had to check that the engine would last the race. If they saw a perfect condition head on the last stage of the rally they generally added some timing, a good friend of mine was a engine tuner with TTE...
Ahaaaa, weren't they banned from Group B for cheating with the restrictors???? just kiddingEdited by GTRCLIVE on Sunday 15th January 06:36
http://homepage.virgin.net/shalco.com/tte_ban.htm
Edited by harry b on Sunday 15th January 09:46
great post so far, I must say that I never heard this pinking noise, that is audible in these clips especially the one Harry posted.
I assume this shrieking klicking is what you refer to pinking ?
However I noticed that engine sound got harder with more advancing and there was a noticable increase in power at least to me.
I have now avanced the engine to a point where it started sounding harsher and have retarted it from there 3 degrees which should be a good compromise between max power and reliablilty.
There is enough beef in that LS7 anyway so no need to stress it in race like conditions. I use 95 octane fuel. I still have some loss of power in mid range heavey load accelearting at certain conditions and I am pretty sure now that certain areas need some more fuel, as the closed loop is either not fast enough or not delivering enough in this condition. In general I can also verify the TAU problem which is more obvious when running closed loop, as this is leaning the engine out and then under certain condition there is lean situations that are noticable as loss of power. So getting the closed loop working perfectly seems to be a science by itself.
I assume this shrieking klicking is what you refer to pinking ?
However I noticed that engine sound got harder with more advancing and there was a noticable increase in power at least to me.
I have now avanced the engine to a point where it started sounding harsher and have retarted it from there 3 degrees which should be a good compromise between max power and reliablilty.
There is enough beef in that LS7 anyway so no need to stress it in race like conditions. I use 95 octane fuel. I still have some loss of power in mid range heavey load accelearting at certain conditions and I am pretty sure now that certain areas need some more fuel, as the closed loop is either not fast enough or not delivering enough in this condition. In general I can also verify the TAU problem which is more obvious when running closed loop, as this is leaning the engine out and then under certain condition there is lean situations that are noticable as loss of power. So getting the closed loop working perfectly seems to be a science by itself.
spatz said:
great post so far, I must say that I never heard this pinking noise, that is audible in these clips especially the one Harry posted.
I assume this shrieking klicking is what you refer to pinking ?
However I noticed that engine sound got harder with more advancing and there was a noticable increase in power at least to me.
I have now avanced the engine to a point where it started sounding harsher and have retarted it from there 3 degrees which should be a good compromise between max power and reliablilty.
There is enough beef in that LS7 anyway so no need to stress it in race like conditions. I use 95 octane fuel. I still have some loss of power in mid range heavey load accelearting at certain conditions and I am pretty sure now that certain areas need some more fuel, as the closed loop is either not fast enough or not delivering enough in this condition. In general I can also verify the TAU problem which is more obvious when running closed loop, as this is leaning the engine out and then under certain condition there is lean situations that are noticable as loss of power. So getting the closed loop working perfectly seems to be a science by itself.
I hope you're not running closed loop when you're fiddeling around with ecu settings. It doesn't help, and can setup your fueltables generated by the closed loop feedback, at least that's how the more advanced ecu's work. It will give a lot of confusion in the readouts, because the ecu will try to compensate, and it doesn't know that you moved the goalposts.I assume this shrieking klicking is what you refer to pinking ?
However I noticed that engine sound got harder with more advancing and there was a noticable increase in power at least to me.
I have now avanced the engine to a point where it started sounding harsher and have retarted it from there 3 degrees which should be a good compromise between max power and reliablilty.
There is enough beef in that LS7 anyway so no need to stress it in race like conditions. I use 95 octane fuel. I still have some loss of power in mid range heavey load accelearting at certain conditions and I am pretty sure now that certain areas need some more fuel, as the closed loop is either not fast enough or not delivering enough in this condition. In general I can also verify the TAU problem which is more obvious when running closed loop, as this is leaning the engine out and then under certain condition there is lean situations that are noticable as loss of power. So getting the closed loop working perfectly seems to be a science by itself.
Why would you want to run closed loop anyway, apart from the legal requiremnts set by TÜV in order to get your green 4 sticker. It should only be functional under constant load and up to about 3500 rpm.
Again I try to put things simple and not too complex for the amateurs, which I count myself too.
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