AFR tuning theory
Feb 5, 2010 | 03:24 PM
#61
Well I decided to test this little theory...since I just love trying new things, especially with tuning.
So basically I moved peak torque to 12's and then peak horsepower to 11.5's
Previously it was 11.5 peak TQ and 11.0 peak HP.
This is from VDR 3rd gear pull. Everything was the same on the map, except fueling changed.
Notice the gain 5000 to 7000 (green/yellow) in TQ and HP. 93 octane Shell V-Powa
Mods listed below...
So basically I moved peak torque to 12's and then peak horsepower to 11.5's
Previously it was 11.5 peak TQ and 11.0 peak HP.
This is from VDR 3rd gear pull. Everything was the same on the map, except fueling changed.
Notice the gain 5000 to 7000 (green/yellow) in TQ and HP. 93 octane Shell V-Powa
Mods listed below...
your air temps dropped 50* too though....
Feb 5, 2010 | 04:56 PM
#62
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Joined: Oct 2008
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From: Houston
x2 
You'd never want to tune for 12.5 AFR on a track car. Let's completely ignore detonation. That extra fuel injected when you're running ~11.0 AFR carries away heat in the intake charge when the atomized charge phase changes from a liquid to a gas... aka evaporates. The heat that was previously present in the combustion chamber charge is now contained in the faster-moving gas-phase gasoline particles.
We all know gasoline doesn't have as high of a latent heat of vaporization as, say, methanol does.... but it's enough to keep a high HP engine from melting something. No high-output 4B11T is going to last under sustained WOT conditions @ 0.85 lambda unless you are running something other than pump ****. i.e. E85. That extra heat is going to melt something - remember, pistons are aluminum. 2618 aluminum (used in high-strength forged pistons) has a melting point of about 950 degrees F. Combustion temperature inside a high-output turbocharged engine is well over 2000 degrees. Guess what happens when that heat overcomes the boundary layer around the piston crown, and any carbon deposits that are on the surface of the piston?
CP 2618 alloy forged piston from a ~600 WHP 3.0 L V6 @ 23 psi
Granted, some detonation was occurring during that
... basically the engine was tuned for 12.2 AFR @ WOT with a huge shot of methanol, and minimal knock (count of 2, intermittent). This happened during a sustained 160 mph pull... on a closed road. Just too little fuel, but minimal knock because of the shot of methanol + water.
YMMV as always, but just remember 12.x AFR is not safe for sustained WOT operation on pump gas. Plain and simple.
You'd never want to tune for 12.5 AFR on a track car. Let's completely ignore detonation. That extra fuel injected when you're running ~11.0 AFR carries away heat in the intake charge when the atomized charge phase changes from a liquid to a gas... aka evaporates. The heat that was previously present in the combustion chamber charge is now contained in the faster-moving gas-phase gasoline particles.
We all know gasoline doesn't have as high of a latent heat of vaporization as, say, methanol does.... but it's enough to keep a high HP engine from melting something. No high-output 4B11T is going to last under sustained WOT conditions @ 0.85 lambda unless you are running something other than pump ****. i.e. E85. That extra heat is going to melt something - remember, pistons are aluminum. 2618 aluminum (used in high-strength forged pistons) has a melting point of about 950 degrees F. Combustion temperature inside a high-output turbocharged engine is well over 2000 degrees. Guess what happens when that heat overcomes the boundary layer around the piston crown, and any carbon deposits that are on the surface of the piston?
CP 2618 alloy forged piston from a ~600 WHP 3.0 L V6 @ 23 psi
Granted, some detonation was occurring during that
... basically the engine was tuned for 12.2 AFR @ WOT with a huge shot of methanol, and minimal knock (count of 2, intermittent). This happened during a sustained 160 mph pull... on a closed road. Just too little fuel, but minimal knock because of the shot of methanol + water.YMMV as always, but just remember 12.x AFR is not safe for sustained WOT operation on pump gas. Plain and simple.
Its up to the tuner to get you the best power within a safe margin. You have to know what to look for. Most "tuners" just go full rich and call it a day. To me thats a bit lazy..
But yes for endurace vehicles or top speed runs like the mile, on pump gas you'd want to stay richer. I prefer to use better gas but thats not always an option.
Feb 5, 2010 | 06:23 PM
#63
Evolving Member
Joined: Oct 2009
Posts: 438
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From: SL, UT
Did you look at your plugs while tuning to see how much boundry layer you actually had? Some engines can run leaner mixtures and still have a decent boundry layer.. Some can't. Mixture tolerance is very engine/setup specific.. Pre-ignition melts pistons. Detonation (knock) cracks pistons and porcelin.. Detonation can disrupt the boundry layer and allow heat to build up and eventually cause pre-ignition. Pre-ignition can also happen without detonation and usually occurs right ABDC where the mixture is the easiest to ignite. And alot of engines can run perfectly fine with light to mild detonation countinuously. I've seen studies done on this..
Its up to the tuner to get you the best power within a safe margin. You have to know what to look for. Most "tuners" just go full rich and call it a day. To me thats a bit lazy..
But yes for endurace vehicles or top speed runs like the mile, on pump gas you'd want to stay richer. I prefer to use better gas but thats not always an option.
Its up to the tuner to get you the best power within a safe margin. You have to know what to look for. Most "tuners" just go full rich and call it a day. To me thats a bit lazy..
But yes for endurace vehicles or top speed runs like the mile, on pump gas you'd want to stay richer. I prefer to use better gas but thats not always an option.
But no, I wasn't really monitoring the plugs during tuning. I wasn't really that serious about keeping that particular engine together. lol. Different story on my Evo X.Pre-ignition definitely destroyed that piston, but you do bring up some good points.
Light detonation is never anything to worry about - hell I saw over 5 counts of knock when I was tuning stock Evo X's. Could be that the tune doesn't adjust perfectly for my elevation, but I'm sure engine longevity would have been just fine on the stock tune.
I actually will give you that the 4B11T seems to handle a leaner mixture without any ill side-effects. I'll probably tune mine for 12.2 AFR once everything is built. I will have to increase my methanol shot size, but all should be fine!
I'm actually contemplating my own timing map because my top-end timing seems too low. I might start up a new thread about the ideal timing map for a 4B11T with a upgraded stock-frame turbo...
Last edited by UT_EvoX; Feb 5, 2010 at 06:25 PM.
Feb 5, 2010 | 06:27 PM
#64
well on the topic of knocksum, I find that on a untuned evo you can hit upto 8KS and not really notice anything (or hear anything)
but if you tune that car and then hit 8 KS you can definatley hear the knock...
but if you tune that car and then hit 8 KS you can definatley hear the knock...
Feb 6, 2010 | 10:24 AM
#66
Feb 6, 2010 | 11:03 AM
#67
funny this caught my eye and old dsm buddy back in the day use to say "your car will never run as fast as it will right before it explodes/melts/brakes" so for an IX would you start at 12.5 then ramp down to high 11s?
Feb 9, 2010 | 09:56 AM
#68
I am far from an expert on AFR tuning theory but I have a couple concerns.
First, I understand about ideal gas laws, burn temps and so on. What I am not so sure about is AFR tuning at 12.5 with zero boost vs. 12.5 with say 25 psi of boost. Certainly it would seem that cylinder pressure will substantially increase heat within the cylinder before, during, and after the burn. Thus EGTs would be substantially higher in the boosted application. I do not believe that this lean of a mixture would be possible (safely) in a boosted application.
Second, comes the issue of timing to achieve 12.5 afr. We all know the simple way to reduce/eliminate knock is to reduce timing and/or add fuel. There is a point of diminished returns though. Going into negative timing certainly poses issues.
As others on here have stated.....there is a fine balance. We push the limits too much things fail.
The tried and true 12.5 afr during spool up to peak boost then rapidly taper to mid 11s and hold to redline offers great power and a very good margin of safety. From here there is still room to adjust the AFR up or down depending on the conditions of the air. Also, this method leaves room for tuning the timing as well.
First, I understand about ideal gas laws, burn temps and so on. What I am not so sure about is AFR tuning at 12.5 with zero boost vs. 12.5 with say 25 psi of boost. Certainly it would seem that cylinder pressure will substantially increase heat within the cylinder before, during, and after the burn. Thus EGTs would be substantially higher in the boosted application. I do not believe that this lean of a mixture would be possible (safely) in a boosted application.
Second, comes the issue of timing to achieve 12.5 afr. We all know the simple way to reduce/eliminate knock is to reduce timing and/or add fuel. There is a point of diminished returns though. Going into negative timing certainly poses issues.
As others on here have stated.....there is a fine balance. We push the limits too much things fail.
The tried and true 12.5 afr during spool up to peak boost then rapidly taper to mid 11s and hold to redline offers great power and a very good margin of safety. From here there is still room to adjust the AFR up or down depending on the conditions of the air. Also, this method leaves room for tuning the timing as well.
Apr 10, 2010 | 11:28 AM
#70
i've been thinking about this quite a bit since reading hartman's book. i don't remember him explicitly saying it, but essentially faster flame speed necessitates reduced timing if already at or past mbt? this whole AFR and timing has been bouncing around in my head.
i imagine it is true for e85 also, but i wanted to at least ask - richer means faster flame speed, right?
i imagine it is true for e85 also, but i wanted to at least ask - richer means faster flame speed, right?
May 1, 2010 | 12:02 AM
#71
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From: Bay Area, SF, CA
An interesting discussion. I read this article the other day which jives somewhat with the thrust of this thread and seems well informed / founded:
http://www.innovatemotorsports.com/resources/rich.php
http://www.innovatemotorsports.com/resources/rich.php
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