Gruppe M intake installed
03-13-2009, 09:00 AM
#31
not just the MAF sensor alone, however.......
throttle position, manifold pressure, intake air temp, engine speed, coolant temp, oil temp, O2 sensor..... all are inputs into the ECU.
The amount of fuel that can be delivered is also partially limited by the capacity of the injectors. For instance, when your engine is cold, signals from the coolant temp sensor and oil temp sensor makes the ECU run a very rich A/F ratio. Sometimes as low as 5:1. With that much fuel being pumped out the injectors, there is no way the injectors have enough time above 7000 rpm to supply the adequate amount of fuel at cold temps. that is why there is a 7000 rpm cutoff for fuel until the temp is up to 125 degrees.
The duration of the intake stroke at 8000 rpm, for instance, is only 3.75 milliseconds. That is basically the maximum amount of potential time the injector has to deliver fuel into the combustion chamber. When fuel volume demand is high, such as in cold start conditions, this simply isn't enough time given the size of the stock injectors and their duty cycle. When the engine is warmer and the fuel requirement diminishes relative the air requirement, there is enough time and your 7K rev limiter is shut off.
Anyway, I LOVE talking about this stuff and could ramble on and on, but the bottom line is that there are multiple ECU inputs that go into determining fuel delivery. Not sure exactly how simple or complex the Audi fuel maps are, however. Maybe they do just look at one or two parameters, or maybe different parameters under differing conditions. That part I don't know. Maybe ELEVENS who has done actual ECU programming can shed more light on this?
The amount of fuel that can be delivered is also partially limited by the capacity of the injectors. For instance, when your engine is cold, signals from the coolant temp sensor and oil temp sensor makes the ECU run a very rich A/F ratio. Sometimes as low as 5:1. With that much fuel being pumped out the injectors, there is no way the injectors have enough time above 7000 rpm to supply the adequate amount of fuel at cold temps. that is why there is a 7000 rpm cutoff for fuel until the temp is up to 125 degrees.
The duration of the intake stroke at 8000 rpm, for instance, is only 3.75 milliseconds. That is basically the maximum amount of potential time the injector has to deliver fuel into the combustion chamber. When fuel volume demand is high, such as in cold start conditions, this simply isn't enough time given the size of the stock injectors and their duty cycle. When the engine is warmer and the fuel requirement diminishes relative the air requirement, there is enough time and your 7K rev limiter is shut off.
Anyway, I LOVE talking about this stuff and could ramble on and on, but the bottom line is that there are multiple ECU inputs that go into determining fuel delivery. Not sure exactly how simple or complex the Audi fuel maps are, however. Maybe they do just look at one or two parameters, or maybe different parameters under differing conditions. That part I don't know. Maybe ELEVENS who has done actual ECU programming can shed more light on this?
03-13-2009, 09:54 AM
#34
Backing up Jenner further.. and for discussion...
The R8 has the setup described and is 420hp as well...
There is something else at play in my opinion. Perhaps it is as simple as the Cats, but Audi doesnt want to say that.
There is something else at play in my opinion. Perhaps it is as simple as the Cats, but Audi doesnt want to say that.
03-13-2009, 10:15 AM
#35
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John do you have plans to do this?
If anyone is planning on getting this work done let me know, I would be interested if I could find a shop that did a decent job at it and followed these specs. What would be very interesting is if someone dyno'd before, after intake manifold ported, then after gruppe M intake added, then after full aftermarket exhaust, and then maybe after a set of high flow cats. Very curious to see what the incremental steps in power increase are. I am still not sold on chips for this car, since as has been mentioned, it is normally aspirated and the stock setup seems to do very well.
I might trickle down this path but will take ma some time, and living where I do I don't necessarily have the resources close by.
I might trickle down this path but will take ma some time, and living where I do I don't necessarily have the resources close by.
03-13-2009, 10:56 AM
#36
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I understand and agree, but this is only an intake...
and I have a hard time believing that the ECU is not programmed to handle air flow increases of the small amounts here. We are not talking about forced induction here, just opening up (and maybe cooling) the intake a bit. It seems very unlike to me that the slight differences in intake air volume would not be accounted for in the map, and I would think there is adequate headroom in the injectors to account for the increased intake charge.
I admit I have never programmed an ECU. But am working on a non-MAF system (speed-density) that makes life a PITA because you have to estimate the signal that you could be directly measuring from the MAF. If you look at the way the thing works - and correct me if I am wrong, please - the ECU primarily uses the MAF reading to get air volume coming into the engine. Then based on throttle position and engine speed, it maps the duration and timing of both the injector cycle and spark. So as long as that MAF signal value has a place in the EFI spreadsheet, then the computer will do just the right thing. In this case, how much can that be? 2-3%?
Now if you go and bolt on a supercharger, you all of a sudden have MAF air signals that are "off the charts".
So what I am saying is that a cold air intake has the potential to provide some gains without reprogramming the ECU, but only if the stock airbox is a real limiter. It was shown not to be in the S4, but this car moves much more air and has a very similar box. So maybe there is some headroom? The few hp claimed seems reasonable to me.
I admit I have never programmed an ECU. But am working on a non-MAF system (speed-density) that makes life a PITA because you have to estimate the signal that you could be directly measuring from the MAF. If you look at the way the thing works - and correct me if I am wrong, please - the ECU primarily uses the MAF reading to get air volume coming into the engine. Then based on throttle position and engine speed, it maps the duration and timing of both the injector cycle and spark. So as long as that MAF signal value has a place in the EFI spreadsheet, then the computer will do just the right thing. In this case, how much can that be? 2-3%?
Now if you go and bolt on a supercharger, you all of a sudden have MAF air signals that are "off the charts".
So what I am saying is that a cold air intake has the potential to provide some gains without reprogramming the ECU, but only if the stock airbox is a real limiter. It was shown not to be in the S4, but this car moves much more air and has a very similar box. So maybe there is some headroom? The few hp claimed seems reasonable to me.
03-13-2009, 11:04 AM
#37
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Go up to John's post above and look in the notes beside the dynoplot
"increase in mass air flow is automatically compensated for with the correct amount of fuel so that target lambda is met (ie reflash not necessary)."
That is what I am saying about the intake.
That is what I am saying about the intake.
03-13-2009, 11:40 AM
#38
AudiWorld Super User
Roger that
Ironically, I'd be more concerned with the aftermarket intake flowing LESS air rather than more.
Good luck with the speed-density system. They are a royal PITA to program and need to be reprogrammed with every little tweak or mod. Car makers probably thought they'd save a few bucks by using a MAP sensor instead of a MAF sensor.
Good luck with the speed-density system. They are a royal PITA to program and need to be reprogrammed with every little tweak or mod. Car makers probably thought they'd save a few bucks by using a MAP sensor instead of a MAF sensor.
03-13-2009, 12:06 PM
#39
I think all our questions and concerns only come into play above 5500rpm......
That's were the performance of the S4 and RS4 motors really begin to diverge. Then the final 1000 rpm of the RS4's power band become a major issue simple due to the length of time available for the injector to deliver fuel, even if the airflow increase is only slight.
Does anyone know if the RS4 uses the same injectors as the S4? if this is in fact the case, and these injectors are truly maxed out in the stock RS4 application, then even a small bump in airflow above stock levels could tirgger the CEL as the injectors would be incapable of maintaining a "within spec" A/F ratio.
Does anyone know if the RS4 uses the same injectors as the S4? if this is in fact the case, and these injectors are truly maxed out in the stock RS4 application, then even a small bump in airflow above stock levels could tirgger the CEL as the injectors would be incapable of maintaining a "within spec" A/F ratio.