MAF or MAP
01-02-2005, 12:17 PM
#31
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If you have a perfect transfer function then the A/F will remian the same even if you change turbo or do other modifications. This doesn't mean that you don't want to reprogram the chips for that setup though. For a different turbo you will want different A/F in the spool up region and with different setups or even with the same setup and a different boost level you may want to change ignition timing.
In theory the AFM chips would also be able to give correct A/F for different airflow. In practice it seems that the transfer function is not perfect, maybe because we push the limit of the AFM and then get large devitions caused by the logarithmic flow/voltage curveform.
In theory the MAP kit could do the same. In practice it would be very difficult (maybe an understatement) to find a good transfer function from MAP/rpm => volt => flow. And since this function will change with every modification on the engine it's up to the owner of the car to work it out. But if you have to much spare time this may be a way to use it. Another severe shotcomming of the Link MAP PB is that there is no MAT compensation (not in the kits I've seen anyway). Some kits use the stock AFM temp sensor to give a correction for ambient temperature but none seems to correct for manifold temperature which is the one that counts.
Special Tool: I'm glad the we agree nowadays!
I suppose it's to much to expect that Jeremy also agrees with me...
Tomas
In theory the AFM chips would also be able to give correct A/F for different airflow. In practice it seems that the transfer function is not perfect, maybe because we push the limit of the AFM and then get large devitions caused by the logarithmic flow/voltage curveform.
In theory the MAP kit could do the same. In practice it would be very difficult (maybe an understatement) to find a good transfer function from MAP/rpm => volt => flow. And since this function will change with every modification on the engine it's up to the owner of the car to work it out. But if you have to much spare time this may be a way to use it. Another severe shotcomming of the Link MAP PB is that there is no MAT compensation (not in the kits I've seen anyway). Some kits use the stock AFM temp sensor to give a correction for ambient temperature but none seems to correct for manifold temperature which is the one that counts.
Special Tool: I'm glad the we agree nowadays!
I suppose it's to much to expect that Jeremy also agrees with me...Tomas
01-02-2005, 12:20 PM
#32
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Hosrom, others responded to your questions (thank you Tomas, Awilson and SpecialTool). One issue was left out, is TIMING!!! Using a AFM chip with a MAF (where the voltage curves are VERY different), you will have problems picking up timing values "especially" at part throttle.
The problem of using AFM chips with MAF becomes more pronounced with MAF calibrated for big HP.. as the voltage curve becomes VERY different than the AFM curve.
Of course there are other issues to deal with other than the transfer function....
Come Feb. There will be a MAF surprise for you guys
The problem of using AFM chips with MAF becomes more pronounced with MAF calibrated for big HP.. as the voltage curve becomes VERY different than the AFM curve.
Of course there are other issues to deal with other than the transfer function....
Come Feb. There will be a MAF surprise for you guys
01-02-2005, 12:30 PM
#34
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Hos, if the DME, ( through a reprogrammed transfer function) is matched to the signal characteristics of the flow sensor, it will interpret the flow correctly and provide the correct duty cycle and thereby intended AFR ( defined in the maps), regardless of the flow or boost levels and regardless of which turbo is used as long as the sensors, injectors or DME is not maxed out. You will therefore not need new chips for other boost levels and you can do the fine tuning with the PB if you want a slightly richer mixture at higher boost for cooling or whatever.
Bengt
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01-02-2005, 02:12 PM
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I'm sure there are other vendors with MAF chips, at least APE makes special chips for their MAF kit, I can't say anything about what's changed in them or if they are good or bad.
I also must point out that I was talking about MAF chips and what could be done with them in general, I have no knowledge of the Vitesse MAF chip and the changes in it.
Tomas
I also must point out that I was talking about MAF chips and what could be done with them in general, I have no knowledge of the Vitesse MAF chip and the changes in it.
Tomas
01-02-2005, 02:15 PM
#37
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My take on the MAP vs. MAF is support (stand alone MAP aside). My experience is that you are pretty much on your own with the Link MAP. In fact, the most help I've had with the MAP system is on this board. Further, to add insult to injury the person that I receive the most help from doesn't even sell the MAP system (FAST951 and thank-you again). The stumble off idle is still there (very minor now).
On the positive side the changes that I’ve made to my car over time (removal of the CV, changing the wastegate, changing to a three inch exhaust with a high flow cat, and cranking up the boost) that affects the A/F ratios merely required minor retuning to the MAP. Also, when the boost tube pooped off during a trip Baby was still very drivable.
However, having someone to call that reponse for assistance wins hands down. Only when the Link MAP system has the support that Fast951 gives his customers could I recommend it. And if Fast951 did carry the Link MAP there is no question in my mind that it would much better sorted out.
Go with FAST951 MAF and know that support is merely a telephone call (or post) away.
On the positive side the changes that I’ve made to my car over time (removal of the CV, changing the wastegate, changing to a three inch exhaust with a high flow cat, and cranking up the boost) that affects the A/F ratios merely required minor retuning to the MAP. Also, when the boost tube pooped off during a trip Baby was still very drivable.
However, having someone to call that reponse for assistance wins hands down. Only when the Link MAP system has the support that Fast951 gives his customers could I recommend it. And if Fast951 did carry the Link MAP there is no question in my mind that it would much better sorted out.
Go with FAST951 MAF and know that support is merely a telephone call (or post) away.
01-02-2005, 03:45 PM
#39
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That is BS about Link support. Performance Developemnts suport Link very well, as does Link Electro Systems in NZ. The stumbling is a tuning issue, not product. Link in NZ have spent MANY ours on the phone and personally with me. Heck, one of the guys there even hekped me tune it.
01-02-2005, 06:19 PM
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Hi guys - this is again a great discussion about MAF and MAP 
I'm playing around with these toys for a while now and just want to share (and discuss) my experiences so far. Generally I prefer the MAP path for turbo engines and the MAF measurement for NA engines. Main reason is that the measurement range is limited for NA engines (0-0,8 bar vs. 0-2+ bar). Additionally in the original 951 environment, the BOV causes some backflow with MAF sensors.
I just adapted a Bosch HFM5 MAF Sensor to the 944S2 engine. The goal in mind was to get a AFM – compatible MAF Sensor. That was (kind of) easy to achieve. While the AFM measures volume (m3/h) and the MAF mass (kg/h) you just have to recalculate the mass to volume. Here both system signals are compared:
With the conversion of the mass signal to volume (volume=mass/density) you will get a nice signal for your stock DME:
That fits great into the 944 S2:
With the 951, it is different. Even if it is possible to make it run in the stock configuration you have to deal a lot with backflow problems caused by the BOV:
If you use a different configuration, you have to keep the MAF as far as possible away from the BOV. It seems easier for me to take the MAP path for the 951. Even if it is more difficult to tune (with MAF it’s a 1D problem: mass->volume, with MAP its 2D: rpm, pressure -> volume) it gives a lot of advantages. If you don’t use a closed gate-style measurement system you can easily use open BOVs for example.
In both cases I don’t need special chips since both solutions were designed to be AFM compatible. For a single type of car it would make sense do develop a special chip for the new sensor. But I want to use my system in different cars (VW, BMW, …) and it seems easier to calibrate it to a certain sensor than to a certain car.
These are just my personal experiences and I don’t want to offend anybody…
I'm playing around with these toys for a while now and just want to share (and discuss) my experiences so far. Generally I prefer the MAP path for turbo engines and the MAF measurement for NA engines. Main reason is that the measurement range is limited for NA engines (0-0,8 bar vs. 0-2+ bar). Additionally in the original 951 environment, the BOV causes some backflow with MAF sensors.
I just adapted a Bosch HFM5 MAF Sensor to the 944S2 engine. The goal in mind was to get a AFM – compatible MAF Sensor. That was (kind of) easy to achieve. While the AFM measures volume (m3/h) and the MAF mass (kg/h) you just have to recalculate the mass to volume. Here both system signals are compared:
With the conversion of the mass signal to volume (volume=mass/density) you will get a nice signal for your stock DME:
That fits great into the 944 S2:
With the 951, it is different. Even if it is possible to make it run in the stock configuration you have to deal a lot with backflow problems caused by the BOV:
If you use a different configuration, you have to keep the MAF as far as possible away from the BOV. It seems easier for me to take the MAP path for the 951. Even if it is more difficult to tune (with MAF it’s a 1D problem: mass->volume, with MAP its 2D: rpm, pressure -> volume) it gives a lot of advantages. If you don’t use a closed gate-style measurement system you can easily use open BOVs for example.
In both cases I don’t need special chips since both solutions were designed to be AFM compatible. For a single type of car it would make sense do develop a special chip for the new sensor. But I want to use my system in different cars (VW, BMW, …) and it seems easier to calibrate it to a certain sensor than to a certain car.
These are just my personal experiences and I don’t want to offend anybody…
01-02-2005, 07:34 PM
#44
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Originally Posted by Transaxle
Additionally in the original 951 environment, the BOV causes some backflow with MAF sensors.
01-02-2005, 11:20 PM
#45
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What i understand is that by installing a BOV in a MAF system is that you run slightly richer. Don't know exactly how much,, and i also remember there was a thread on 'Which BOV' and rennlisters installing BOV's on MAF, MAP and AFM. I do recall just ONE or TWO cases where the MAF and AFM would have some hesitation and stumbling issues (it was a 3 page thread). BOV's on MAP systems are fine (measuring pressure not air-flow). Anyone else had problems with BOV's on MAF's or AFM's?