MAF mapping and Boost Questions
08-28-2005, 11:42 PM
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MAF mapping and Boost Questions
OK...as to not hijack a thread, I am asking this in a separate thread. Another thread had the following posted:
>>>
Varying boost levels and MAF mapping. As long as you have your MAF mapped correctly throughout the MAF's range at the maximum boost you are going to run it is safe to turn down the boost because the MAP is based on air flow. However, The DME bases it's timing decisions on load. This load, in part is determined by the voltage from the MAF. If you have the MAF mapped for higher boost levels, it will not reach enough voltage at lower boost levels for the DME to think the car is under load. This means the timing will not be advanced at the lower boost levels making the car very sluggish and laggy.
Real world example: I turned my boost down from the 21psi of my 395 rwhp run to 17. Doing some data log runs with my Mafterburner my time from 3000 rpm to 6700 rpm in third gear was 14 seconds with perfect A/F ratios. And yes, if felt sluggish and it wasn't just from turning down the boost. The maximum air flow at 17 psi was only sending 4.2 volts to the DME where at 21 psi it was sending the required 4.6 volts, ie more boost, more flow. I turned down my fuel pressure and remapped the MAF MAP to basically the same A/F ratios but with more voltage going to the DME so the max voltage was once again 4.6 volts. After the re-mapping the data log showed a decrease in time of the 3000 rpm to 6700 rpm run from 14 seconds to only 6 seconds. Quite an improvement timing makes yes it does!
>>>>
This really got me thinking. I have HORRIBLE off-boost peformance and poor spool up. I am starting to believe that some of this could be not the turbo (a k27/6) but my set-up. I have a quite old MAF set-up using autothority chips and MAf system. It has been on the car for at least 8 years now.
I have always thought that my lag an off-boost perfomance was due to high altitude (6000ft). When I live at low altitude for a year and a half (this is when I bought the car) it had much better off boost performance and quicker spool-up. I live in a non-emmision area. Once I moved back to upto high altitude, I moved into an emissions area. To pass emmisions the adjustment pot on the MAF system had to be tweaked. I had a shop with an A/F meter do this.
I have also added a boost controlled and upped the boost. My way of thinking is that I have a 1.1 bar chip set (16psi). This is 1.1 bar gauge or 2.1bar absolute. I however live where the actual atomospheric pressure is around .8 bar. To get to 2.1 bar absolute I need to run about 1.3 bar gauge or about 19 psi of boost. So, I cranked up the boost to 19 psi.
I am actually running rich as when I cranked up the boost, I swapped a 3 bar fuel pressure regulator on. The last dyno pull I did (not a really good dyno or equipemnt and at 8000ft) my A/F hovered between 9.5 and 10.5 to 1. I have run it rich because of my paranoia days of running nitrous. Basically, I loose some hp by running rich instead of an engine by running lean.
I am thinking that my mid range is way too fat to get good spool up. The top may be too fat also. But to add to this my MAF may be way off after reading the other thread and not getting good spark advance.
How do I go through and check the MAF voltage? It seems the easiest way would be to hook a voltmeter in-line. However, when should the MAF peg a 4.6V? This should be at the max flow condition, correct?
Should I go back to the 2.5 bar fuel pressure regulator? How do the chips measure ambient conditions and adjust? If I have a set of 16psi chips, are they really good upto 19psi at my altitude?
I think the best way to do this would be a custom set of chips or at least newer chips. However, to get chips made for high altitude may be hard. Not many of the tuners live here and can't simulate this altitude. Can a car be tuned "remotely" with any degree of sucess?
Do the newer chip tuners actaully do the wonders that I have heard with their chip sets?
Just some thoughts.
-Dana
>>>
Varying boost levels and MAF mapping. As long as you have your MAF mapped correctly throughout the MAF's range at the maximum boost you are going to run it is safe to turn down the boost because the MAP is based on air flow. However, The DME bases it's timing decisions on load. This load, in part is determined by the voltage from the MAF. If you have the MAF mapped for higher boost levels, it will not reach enough voltage at lower boost levels for the DME to think the car is under load. This means the timing will not be advanced at the lower boost levels making the car very sluggish and laggy.
Real world example: I turned my boost down from the 21psi of my 395 rwhp run to 17. Doing some data log runs with my Mafterburner my time from 3000 rpm to 6700 rpm in third gear was 14 seconds with perfect A/F ratios. And yes, if felt sluggish and it wasn't just from turning down the boost. The maximum air flow at 17 psi was only sending 4.2 volts to the DME where at 21 psi it was sending the required 4.6 volts, ie more boost, more flow. I turned down my fuel pressure and remapped the MAF MAP to basically the same A/F ratios but with more voltage going to the DME so the max voltage was once again 4.6 volts. After the re-mapping the data log showed a decrease in time of the 3000 rpm to 6700 rpm run from 14 seconds to only 6 seconds. Quite an improvement timing makes yes it does!
>>>>
This really got me thinking. I have HORRIBLE off-boost peformance and poor spool up. I am starting to believe that some of this could be not the turbo (a k27/6) but my set-up. I have a quite old MAF set-up using autothority chips and MAf system. It has been on the car for at least 8 years now.
I have always thought that my lag an off-boost perfomance was due to high altitude (6000ft). When I live at low altitude for a year and a half (this is when I bought the car) it had much better off boost performance and quicker spool-up. I live in a non-emmision area. Once I moved back to upto high altitude, I moved into an emissions area. To pass emmisions the adjustment pot on the MAF system had to be tweaked. I had a shop with an A/F meter do this.
I have also added a boost controlled and upped the boost. My way of thinking is that I have a 1.1 bar chip set (16psi). This is 1.1 bar gauge or 2.1bar absolute. I however live where the actual atomospheric pressure is around .8 bar. To get to 2.1 bar absolute I need to run about 1.3 bar gauge or about 19 psi of boost. So, I cranked up the boost to 19 psi.
I am actually running rich as when I cranked up the boost, I swapped a 3 bar fuel pressure regulator on. The last dyno pull I did (not a really good dyno or equipemnt and at 8000ft) my A/F hovered between 9.5 and 10.5 to 1. I have run it rich because of my paranoia days of running nitrous. Basically, I loose some hp by running rich instead of an engine by running lean.
I am thinking that my mid range is way too fat to get good spool up. The top may be too fat also. But to add to this my MAF may be way off after reading the other thread and not getting good spark advance.
How do I go through and check the MAF voltage? It seems the easiest way would be to hook a voltmeter in-line. However, when should the MAF peg a 4.6V? This should be at the max flow condition, correct?
Should I go back to the 2.5 bar fuel pressure regulator? How do the chips measure ambient conditions and adjust? If I have a set of 16psi chips, are they really good upto 19psi at my altitude?
I think the best way to do this would be a custom set of chips or at least newer chips. However, to get chips made for high altitude may be hard. Not many of the tuners live here and can't simulate this altitude. Can a car be tuned "remotely" with any degree of sucess?
Do the newer chip tuners actaully do the wonders that I have heard with their chip sets?
Just some thoughts.
-Dana
08-30-2005, 03:05 AM
#2
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Adjusting the MAF voltage...
The main reason for adjusting the MAF voltages is to run more boost than the chips that go with the MAF are designed for. Instead of reprograming the chips every time you want to change boost levels, you adjust the fuel pressure and MAF voltages so the chipset thinks you are running within it's programmed range.
Assuming you have a wide band O2 sensor to see what is going on, you need a way to both monitor and adjust the voltage from the MAF to the DME. The MAFterBurner does this. There are others, but I like the MAFterBurner because it does data logging. With the datalogging you can see A/F ratio, the MAF voltage, and the Voltage sent to the DME over the entire rpm range. It also lets you make a run, then look at the data while sitting still. You tune by the MAF's output voltage, you are making a map of what voltage to send to the DME to get the desired A/F ratio for the entire voltage range of the MAF.
The next thing you need to help massage the signal is an adjustable fuel pressure regulator. Adjusting the fuel pressure really helps to keep the MAF voltage adjustments within the limits of the adjustment range of the MAF tuning device.
The idea is to make a full throttle run in 3rd gear to red line with a maximum of 4.6 volts being sent to the DME with the car tuned to the proper A/F ratios. This can be a bit tricky and take some time. To add fuel you raise the voltage going to the DME for the corresponding MAF output voltage. If you increase the maximum to 4.6 volts sent to the DME and the A/F ratio is still too lean. you need to raise the fuel pressure. If you are not reaching a maximum of 4.6 volts to the DME and the car is running too rich you need to lower the fuel pressure and raise the voltage. If you are going over 4.6 volts maximum to the DME ignore anything above the 4.6 mark. The DME does not know what to do when the voltage is above 4.6 and the resulting A/F ratios can be very misleading.
It is important to retune Map for A/F over the entire MAF range each time the fuel pressure is changed because the injector flow outputs will change over their operating range at different fuel pressures. You will find yourself lowering the fuel pressure to get the peak voltage, and then as you bring the lower end of the curve in line you will need to raise the fuel pressure. This is because as the car gets closer to a good tune it will flow more air (and make more power). A good place to start if you are running higher boost and bigger injectors is the fuel pressure the injectors are flowed at, ie. 43 psi.
The main reason for adjusting the MAF voltages is to run more boost than the chips that go with the MAF are designed for. Instead of reprograming the chips every time you want to change boost levels, you adjust the fuel pressure and MAF voltages so the chipset thinks you are running within it's programmed range.
Assuming you have a wide band O2 sensor to see what is going on, you need a way to both monitor and adjust the voltage from the MAF to the DME. The MAFterBurner does this. There are others, but I like the MAFterBurner because it does data logging. With the datalogging you can see A/F ratio, the MAF voltage, and the Voltage sent to the DME over the entire rpm range. It also lets you make a run, then look at the data while sitting still. You tune by the MAF's output voltage, you are making a map of what voltage to send to the DME to get the desired A/F ratio for the entire voltage range of the MAF.
The next thing you need to help massage the signal is an adjustable fuel pressure regulator. Adjusting the fuel pressure really helps to keep the MAF voltage adjustments within the limits of the adjustment range of the MAF tuning device.
The idea is to make a full throttle run in 3rd gear to red line with a maximum of 4.6 volts being sent to the DME with the car tuned to the proper A/F ratios. This can be a bit tricky and take some time. To add fuel you raise the voltage going to the DME for the corresponding MAF output voltage. If you increase the maximum to 4.6 volts sent to the DME and the A/F ratio is still too lean. you need to raise the fuel pressure. If you are not reaching a maximum of 4.6 volts to the DME and the car is running too rich you need to lower the fuel pressure and raise the voltage. If you are going over 4.6 volts maximum to the DME ignore anything above the 4.6 mark. The DME does not know what to do when the voltage is above 4.6 and the resulting A/F ratios can be very misleading.
It is important to retune Map for A/F over the entire MAF range each time the fuel pressure is changed because the injector flow outputs will change over their operating range at different fuel pressures. You will find yourself lowering the fuel pressure to get the peak voltage, and then as you bring the lower end of the curve in line you will need to raise the fuel pressure. This is because as the car gets closer to a good tune it will flow more air (and make more power). A good place to start if you are running higher boost and bigger injectors is the fuel pressure the injectors are flowed at, ie. 43 psi.
08-30-2005, 12:19 PM
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DanaT, You have many issues contributing to your setup..
- Lag: Can be caused by overly rich mixture. The altitude does not help much either.
- Rich Mixture: Primarely software - MAF can be faulty as well.
The DME reads the altitude switch and compensates properly.
- Lag: Can be caused by overly rich mixture. The altitude does not help much either.
- Rich Mixture: Primarely software - MAF can be faulty as well.
The DME reads the altitude switch and compensates properly.
08-30-2005, 01:30 PM
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The ignition maps in the autothority MAF chips are really odd and nothing I would use. Also their transfer funktion is less than perfect. Don't try to tweak this system, get a better one. I am sure John can help.
Bengt
Bengt
08-30-2005, 01:40 PM
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Much of your difficulties comes from not having a maf meter sized close to the stock afm output. There are ways of compensating a larger meter as RKD notes. But for ease of tuning its better to have a meter sized close to the stock afm.