Detonation and EGT.
03-02-2007, 06:51 AM
#1
Detonation and EGT.
I have read and been told that the richer the mixture the lower the egt's and same for leaning out. the leaner it is the lower the egt, which means that higher EGT does not mean leaner like most of us think. I belive that stoich is where the EGT is at its highest. Now my question is, how come if one leans out too much, why does it cause detonation? if your running lean shouldnt temp's be lower and therefore not cause hotspots within the cylinders? OR is it that by leaning out one reaches 14.7 which is the hottest temp possible, and that is why we tune below that, 12's for boost 13's for n/a. Ofcourse there wont be any real power but just for theory, if we put the mixture really lean like at 16.5 for example, will that cause detonation or high egt's?
03-02-2007, 10:03 AM
#2
Originally Posted by streetzlegend
I have read and been told that the richer the mixture the lower the egt's and same for leaning out. the leaner it is the lower the egt, which means that higher EGT does not mean leaner like most of us think. I belive that stoich is where the EGT is at its highest. Now my question is, how come if one leans out too much, why does it cause detonation? if your running lean shouldnt temp's be lower and therefore not cause hotspots within the cylinders? OR is it that by leaning out one reaches 14.7 which is the hottest temp possible, and that is why we tune below that, 12's for boost 13's for n/a. Ofcourse there wont be any real power but just for theory, if we put the mixture really lean like at 16.5 for example, will that cause detonation or high egt's?
I have seen on the dyno that egt's are higher at ~13:1 than ~12:1. It is my UNDERSTANDING that ANY leaner = higher egt's. One would think that leaner = more heat = higher egt's. And add detonation, like you said, and very high egt's.
And also from what I read the higher the temp in the comb. chamber, the higher the pressure. Which follows physics..lol. And the ~12.5:1 a/f that "most" tuners use fo FI applications is for safety for error, from what I read. Colder air = denser air= more air in combustion chamber.. hot air = less dense air = less air in the combustion chamber.. just one of thos variables.
03-02-2007, 10:17 AM
#3
Originally Posted by Bags
I have seen on the dyno that egt's are higher at ~13:1 than ~12:1. It is my UNDERSTANDING that ANY leaner = higher egt's. One would think that leaner = more heat = higher egt's. And add detonation, like you said, and very high egt's.
And also from what I read the higher the temp in the comb. chamber, the higher the pressure. Which follows physics..lol. And the ~12.5:1 a/f that "most" tuners use fo FI applications is for safety for error, from what I read. Colder air = denser air= more air in combustion chamber.. hot air = less dense air = less air in the combustion chamber.. just one of thos variables.
And also from what I read the higher the temp in the comb. chamber, the higher the pressure. Which follows physics..lol. And the ~12.5:1 a/f that "most" tuners use fo FI applications is for safety for error, from what I read. Colder air = denser air= more air in combustion chamber.. hot air = less dense air = less air in the combustion chamber.. just one of thos variables.
The reason I am curious about this is because when I was having problems with my o2's. My a/f was extremly lean like at 16.5 and sometimes went up even to 20's with basically no fuel almost. Now when i would accelerate, i can hear the turbo spool up for some reason, something that it never does when a/f is at normal range (at such low rpms 1500-2000). I am just trying to figure out why would the turbo spool up more than usual while attempting to drive (lean a/f's felt like had blown MAF), the car would berly move but u can hear that thing spool up alot. Is it because super lean condition = more pressure since its alot cooler, more pressure = more volume of air going to the turbo?
03-04-2007, 07:51 AM
#8
EGT's will be lower when the mixture is very rich or very lean as far as I know. I'm not sure if stoich is the highest point, but it would make sense as that is the point where all of the fuel and air is burned (i.e. converted to energy). A lean condition means that there is air left over from the combustion process and rich means that not all of the fuel has been burnt.
As for your turbo problem, that sounds like your timing is retarded a large amount. I had the same problems when my knock sensor was going haywire, it would pull timing for no reason. I would get boost whenever I hit the gas, but the car wouldn't really accelerate. This caused extremely high EGTs, around 1500 at part throttle, which is why the turbo spooled so fast. If you can check your egt's and they are very high for no reason, then that is most likely your problem.
As for your turbo problem, that sounds like your timing is retarded a large amount. I had the same problems when my knock sensor was going haywire, it would pull timing for no reason. I would get boost whenever I hit the gas, but the car wouldn't really accelerate. This caused extremely high EGTs, around 1500 at part throttle, which is why the turbo spooled so fast. If you can check your egt's and they are very high for no reason, then that is most likely your problem.
03-04-2007, 10:43 AM
#9
Searching reveals...
and
Here is an interesting graph I lifted from an aviation website (http://www.avweb.com/news/columns/186619-1.html).
The graph was made from data collected on a particular aircraft engine. Aircraft engines commonly use fixed engine rpm and ignition timing, and throttle mixture (afr) is varied for different operations (take-off, cruise, climb, descent, etc.).
The 50 deg rich line corresponds to approximately 12.5:1 afr, and is about where peak power is made. I'm not sure what 50 deg lean corresponds to. ICP refers to the peak combustion pressure after ignition. CHT is the cylinder head temperature.
It is interesting to note that egt peaks at stoichiometric, and falls off for both richer and leaner air-fuel ratios.
Originally Posted by Stephen Max
Originally Posted by Stephen Max
Here is an interesting graph I lifted from an aviation website (http://www.avweb.com/news/columns/186619-1.html).
The graph was made from data collected on a particular aircraft engine. Aircraft engines commonly use fixed engine rpm and ignition timing, and throttle mixture (afr) is varied for different operations (take-off, cruise, climb, descent, etc.).
The 50 deg rich line corresponds to approximately 12.5:1 afr, and is about where peak power is made. I'm not sure what 50 deg lean corresponds to. ICP refers to the peak combustion pressure after ignition. CHT is the cylinder head temperature.
It is interesting to note that egt peaks at stoichiometric, and falls off for both richer and leaner air-fuel ratios.
03-04-2007, 01:29 PM
#10
Thanx for those finds, I actually read that article after posting this thread. I think i am going to go ahead and purchase EGT gauge just to see where im at. I have tuned my car for high 11's to 12's. I just wanna know where my EGT's are.
03-04-2007, 01:30 PM
#11
Originally Posted by Brad92SE
EGT's will be lower when the mixture is very rich or very lean as far as I know. I'm not sure if stoich is the highest point, but it would make sense as that is the point where all of the fuel and air is burned (i.e. converted to energy). A lean condition means that there is air left over from the combustion process and rich means that not all of the fuel has been burnt.
As for your turbo problem, that sounds like your timing is retarded a large amount. I had the same problems when my knock sensor was going haywire, it would pull timing for no reason. I would get boost whenever I hit the gas, but the car wouldn't really accelerate. This caused extremely high EGTs, around 1500 at part throttle, which is why the turbo spooled so fast. If you can check your egt's and they are very high for no reason, then that is most likely your problem.
As for your turbo problem, that sounds like your timing is retarded a large amount. I had the same problems when my knock sensor was going haywire, it would pull timing for no reason. I would get boost whenever I hit the gas, but the car wouldn't really accelerate. This caused extremely high EGTs, around 1500 at part throttle, which is why the turbo spooled so fast. If you can check your egt's and they are very high for no reason, then that is most likely your problem.
03-04-2007, 01:56 PM
#12
Originally Posted by streetzlegend
Thanx for those finds, I actually read that article after posting this thread. I think i am going to go ahead and purchase EGT gauge just to see where im at. I have tuned my car for high 11's to 12's. I just wanna know where my EGT's are.
Why do you care about your EGT? If you aren't making large timing adjustments and your air fuel is where it should be, there's no need to monitor EGT in my opinion. You tune AFR (which you've already done) and EGT is just a byproduct of that (and timing, as stated above).
03-04-2007, 03:03 PM
#13
I don't even bother with EGT... I tune AFR, and put a reasonable timing curve in the thing.. depending on what type of engine I'm tuning.. that might vary greatly. Long stroke, short rod engines typically like a little more advance.. whereas short stroke/long rod engines usually need a little less advance..
The two best investments you can make.. would be a good wide band 02 monitor, and a nice knock detection system.. like J&S.. Tune the AF with a conservative timing map.. and then advance the timing until it pings.. then, back it down a few degrees from there.
Travis
The two best investments you can make.. would be a good wide band 02 monitor, and a nice knock detection system.. like J&S.. Tune the AF with a conservative timing map.. and then advance the timing until it pings.. then, back it down a few degrees from there.
Travis
03-04-2007, 03:52 PM
#14
well Nealoc, I am tuning via the maf signal using vafc2. I have 370 injectors, which forces me to make even more corrections, so my timing is more advanced than stock, not sure how much. The most correction i have is -13. with 255 walbro, 370 injectors, and stock fuel pressure. I dont know if -13 is advancing too much. Thats why I am curious about my EGT.
03-04-2007, 04:22 PM
#15
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Join Date: Dec 2006
Posts: 78
Lean is very hot, had a friend (not the smartest one) that became addicted to leaning it out a little before each of his races. His car, of course, became faster and faster as a result of this. His engine went out during a race and even melted the radiator fan blades, and the exhaust manifold was also white hot from how lean it was. His knock sensor however, never showed any real signs of excessive knock, according to him.
Still trying to get used to the max thing, but usually you want to pull more and more timing as you add boost, NOT add timing, I would say that this is the source of your problems.
Still trying to get used to the max thing, but usually you want to pull more and more timing as you add boost, NOT add timing, I would say that this is the source of your problems.
03-04-2007, 05:27 PM
#17
Originally Posted by brs2c
Lean is very hot, had a friend (not the smartest one) that became addicted to leaning it out a little before each of his races. His car, of course, became faster and faster as a result of this. His engine went out during a race and even melted the radiator fan blades, and the exhaust manifold was also white hot from how lean it was. His knock sensor however, never showed any real signs of excessive knock, according to him.
Still trying to get used to the max thing, but usually you want to pull more and more timing as you add boost, NOT add timing, I would say that this is the source of your problems.
Still trying to get used to the max thing, but usually you want to pull more and more timing as you add boost, NOT add timing, I would say that this is the source of your problems.
Also, advancing the ignition timing past the optimal point, usually results in lower EGT's.. Retarding the timing too much, and running rich, will result in higher EGT's.. because the combustion event isn't happening at the optimal time.. instead of say.. 20* before TDC, it might be happening at 10* before TDC.. this results in combustion that occurs past peak cylinder pressure.. less of the fuel is burned, and actually burns on the way out of the exhaust valve.. giving you a higher EGT reading (fuel burns while passing the probe). This can make things very hot under the hood.. it can also destroy exhaust valves, melt pistons, and in extreme cases, cause damage to the turbine side of the turbocharger. Also, this can lead to heat retention in the combustion chamber/piston crown.. as the heat builds.. detonation occurs more easily.. leading to cracked ring lands/rings, etc..
One of the biggest misconceptions, is that you have to pull a lot of timing on a turbo/blown motor.. you simply run as much timing as the engine wants.. pulling a ton of timing not only hurts numbers.. but, it can do some severe damage to the engine/hot parts.
Travis
03-04-2007, 11:08 PM
#19
Originally Posted by Nealoc187
Why do you care about your EGT? If you aren't making large timing adjustments and your air fuel is where it should be, there's no need to monitor EGT in my opinion. You tune AFR (which you've already done) and EGT is just a byproduct of that (and timing, as stated above).
after you tune your car using a wideband meter you need to know the egt range at any given rpm that way you know if you are really running lean or rich for example sr20dets on 9-10psi on stock turbo stock injectors with a good fuel pump(walbro 255) can run as 1500 degrees and most people agree thats the highest you should go ,on the contrary a 1989 rx7 rurbo can go as high as 2300 degrees and thats the higher on those engines run a sr20det past the 2000 degress and in a few seconds you wil have a meltdown(my experience on my 240sx)
high egt=less fuel(lean)
low egt=unburned fuel
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