Colin 90 C2

Loren,
What I am understanding from you is that MAF is a better sensing scheme as it adjusts for all loads, whether part throttle or full throttle or anywhere in-between.

What I have seen in the past few years is that some of the auto mfgs are using MAP sensors instead of MAF.
What are the benefits to this this design? I know that cost is probably the major factor as a MAP sensor is way cheaper than a MAF. More importantly though, what are the drawbacks?

Laurence Gibbs

Fair enough Loren. As you say it's easy to interpret things wrongly in forum posts.

Lorenfb

"What I have seen in the past few years is that some of the auto mfgs are using MAP sensors instead of MAF.
What are the benefits to this this design? I know that cost is probably the major factor as a MAP sensor is way cheaper than a MAF. More importantly though, what are the drawbacks?"

You're correct about:
MAF is the best when combined with TPS (throttle position), e.g. Porsche & BMW now.

MAP Negatives:
MAP is cheaper, but has inherent errors, e.g. engine not running (no vacuum) - full rich,
and as the engine wears it has less vacuum thus MAP sensing goes richer.

Geoffrey

"And that's why ALL OEMs don't use MAF, but now have learned
from Motec to use A-N only. RIGHT!!!!!!!!!!"

I believe the real reasons that the OEMs tend to use a MAF as load measurement is due to emissions requirements for 100k. A MAF will allow for consistent fueling as the engine's VE% decreases as the engine wears. We're talking about minor amounts, not the difference between good running and poor running.

MoTeC can do MAP, MAF, TPS for load measurements.

NineMeister

Loren, why don't you re-read my comment in the context of answer to Laurence's question, rather than having a dig based on how you want to interpret it? To put it simply so everyone understands my comment: in the stock Motronic function there is a "blind zone" where the AFM is at full scale deflection and the WOT switch is open circuit, and in this zone the engine effectively runs on a 2D rpm only table. In comparison to this zone of operation within Motronic yes, I believe that Motec on 3D Alpha-N (along with the usual MAP/BAP corrections) is more accurate since it is not relying on just RPM to decide how much fuel to put in, OK?


It also appears that the interpretation of flippancy within a post is directly proportional to the number of exclaimation marks and capital letters used in the post, so if you want to comment without trying to wind everyone up can I politely suggest that you just try a few less? All the best.

Lorenfb

"in the stock Motronic function there is a "blind zone" where the AFM is at full scale deflection and the WOT switch is open circuit, and in this zone the engine effectively runs on a 2D rpm only table. In comparison to this zone of operation within Motronic yes, I believe that Motec on 3D Alpha-N (along with the usual MAP/BAP corrections) is more accurate since it is not relying on just RPM to decide how much fuel to put in, OK?"

Blind spot? Not really, if everything is adjusted properly. What is gained by adding an A-N system
for the very small end throttle position versus the WOT switch is very negligible. Hardly a reason
to switch an A-N system, as little to NO real AFR improvements which yield more torque are gained.

Again, where're the data to prove such? Remember, the torque improvement
with AFRs from 11 to 13 are very negligible. So trying to tweak there, e.g. A-N,
is questionable.

NineMeister

Loren, this is not a debate about the merits of Motec, Alpha-N or the like, we have already been there and done it to near death, however I am glad that at least in principle you agree that there is a "blind spot" within the stock 964 programming which confirms my answer to Laurence's question.

SimonExtreme

Geoffrey

You will be pleased to know that I did a net search to find the answer and ever site I have seen gives this exact reason for MAF being prefered. I should have waited for your post


Loren
During the same search, this was covered and the reason given were 2 fold. One you mention, that it is cheaper. The other that is regularly mentioned is that MAP sensors are less likely to go wrong. (Don't shoot the messenger, just quoting/summarising a few websites )

Lorenfb

"The other that is regularly mentioned is that MAP sensors are less likely to go wrong."

That's possibly the case. I've only seen data for MAF, and the 993 & 996 have fairly
high failure rates. Not good when compared to the good old AFM which basically lasts
forever if lubricated.

Red rooster

Geoffrey,
Sorry, sorry . MAF=Mass Air Flow !! Slip up on my part thinking more about the benifits than measured parameters . Slap on wrist now done !!

Loren,
I was very interested in your comment that both 993 and 996 have MAF reliability issues. My European market experience is that the 993 HFM2 is very reliable whereas the 996 HFM5 is cr*p ! Got me wondering why the HFM2 is giving problems in the USA ?


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A MAP sensor system is often used with a low cost single point injection system, combined with a really tame cam profile where accurate motor modelling allows decent calibration.
Any motor using a vigourous cam would have problems using MAP as the load input .
In OEM terms the cost variation between a MAP and MAF sensor would not be a reason for selecting one over the other.

All the best

Geoff

Geoffrey

I will say that in the MoTeC installations I use 2 GM map sensors, one for manifold pressures and one for barometric pressures. Only recently have I been using a Bosch unit when doing 996tt engines and I have yet to see one fail...ever.

In theory, manifold pressure pulsations from agressive camshafts can cause incorrect MAP readings, however, in practice, there are some things you can do to have a stable MAP signal. My engine has camshafts with durations of nearly 320 degrees seat duration and I have a stable MAP reading, with ITBs. On a common plenum manifold, it would be the same or better.

SimonExtreme

I find this quote interesting. On performance cars, I might agree but on the family 4 door, every dollar saved makes a big difference. Take the VW group, where they try to use the same components over 5 different brands, $1 on a car can make literally millions $ difference to the bottom line. Unless that money can be made back due to marketing considerations (better fuel consumption etc) or there is another consideration (emmissions control), I cannot see a major car company choosing an option that was even a lttle bit more money. Add to that reliability and I tend to believe that economics is the reason why MAP is prefered.

Red rooster

Simon,
And the current VAG car using MAP is ? That is not an aggresive question !!

All the best

Geoff

SimonExtreme

Geoff

No idea! I don't know anything about the groups products and nor do I want to! I was using it as an example of how small amounts of money can make a big difference. Having done a quick google, it seems like a number of car use them but I cannot tell if they are current models or not and as it is well past my bed time, I will give up

As I mentioned, the issue of MAP vs MAF was just what I read in various articles on the web. I have little experience of them (MAP)which i hope I had made clear! In fact, I am not sure that I have owned a car with a MAP sensor and although I understand the principal, that's about it.

Red rooster

Simon,
OK. I believe the answer to be none .
If you take a look at most current gas/diesel turbo motors you will find both MAF and MAP ! MAF is the primary load sensor and MAP is a conformation sensor.
I do understand your OE cost point. I have worked for a car company in the past. Bottom line these days is that all designs must comply with emmission requirements. Without that you dont have a product.
The trick is to get there at the lowest cost.
All a bit heavy duty compared to 964 days !

I guess we have wandered way of topic now so I will shut up .

All the best

Geoff