Laurence Gibbs

No one so far has confirmed if my understanding of what's been said is correct or not? I am guessing that this is either because i am so way of it's funny? or no one knows? would like to know if my understanding was twaddle or not. Thanks chaps.

Lorenfb

"lets see if i have this correct when the AFM outputs a voltage via it's variable resistor this voltage is used to look up a load factor in the afm map? This in tern with the other "modifiers" then alters the fuel trim for the required map (idle, partial and wot) to set injector pulse width? Presumably the load factors are created by the characteristics of the AFM itself? So to move to MAF you would need to know the relationship between the load factors and the MAF??
- Laurence Gibbs -

That's it! You're now ready to design your own fuel management system as a competitor to both
Motronic & Motec.

Well said!

Laurence Gibbs

Loren,
I am just trying to understand the thread as much as my limited(very) knowledge will allow. Constructive comments welcome. Flippancy is less well recieved.

Colin 90 C2

Laurence,
There is a good book "How to tune and modify Engine Management systems" by Jeff Hartman that explains theory behind engine management systems. If you have the time, it's a good read.

Geoffrey

Loren, I think we are both right, if the ignitor is an "intelligent" ignitor, then it will clip the current, if the ignitior is a "dumb" ignitor, then the ECU will clip the current. Bosch makes both types as do other manufacturers.

"Not completely true! Since most/all inductive ignition system coils can be used with CDI systems, but NOT all CDI coils can be used with inductive discharge coils."

Yes, it is true that an inductive coil will probably not fail when used with CDI whereas a CDI coil will most certainly fail when used with an inductive ignition. However, since an inductive coil is designed to store energy and the resistance is high, the benefit of the CDI ignition is then compromized which is why I say an inductive coil really shouldn't be used with a CDI system unless it is one of the older non digital systems like an MSD 6A, and even then I'd always recommend using a CDI specific coil.

SimonExtreme

Why stop at those 2? There are so many other ones that can be used on Porsches! My advice to Laurence would be that the market is already saturated. What is clearly needed is more people who understand the ones out there

NineMeister

Yes, in principle. The major advantage to a MAF conversion (or MAP for that matter) is that provided you choose the correct meter, the operating range of the MAF will actually cover the full load/rpm range of the engine, unlike the stock barn-door type airflow meter which goes full scale somewhere around 4500rpm & over 75% throttle (I'm sure someone has the exact figures on file). I would guess that once you have the MAF signal arriving at the ecu replicating the AFM signal you would have to expand the load/rpm fuel/ignition maps to now cover the full operating range of the engine, and then disregard the WOT map completely.

Geoff, I know that you have been through this process, is this about right? What do you do about temperature compensation - do you use the natural temperature compensation of the MAF signal to modify the table numbers or is it preferable to use a seperate temperature sensor?

Red rooster

Colin,
The MAF will take care of air temperature but ignition timing still needs the air temperature signal.
Boy ,this is all a long time ago ! I keep meaning to hook up a 964 system and revisit the whole thing again.Unfortunately the challenges of todays systems keep getting in the way !

All the best

Geoff

Laurence Gibbs

What i want to achieve knowledge wise is just good understanding of the system i have. I have read a few books on the subject mostly ones recommended buy the guys on here, I have'nt read the one you mention Colin C2 so thanks for the recommendation.I think Motec/Bosch are safe for the time being ;-) From what Jason was saying it's mostly the AFM map that requires altering for running MAF. That way you do away with the conversion "box" that some companies use. What does the ecu do between 75% and WOT?

SimonExtreme

If I understand the issues correctly, it is these "boxes" that cause the problems or more precisely, the lack of benefit. I believe that the box converts the MAF signal into the same range and type as the AFM and therefore you don't gain the benefit, other than better airflow. It does seem strange to change a device for one that measures more accurately and then to convert that measurement back into the old data.

Also, unless I have misunderstood, the approach that does work and is on my car is to reprogram/remap the DME.

Maybe Geoff can confirm whether I have got this about right or whether I have made a complete tit of myself

Red rooster

Simon,
In the end what we want is the correct amount of fuel and ignition timing for the load and rpm of the motor. Its one of these situations where there are so many ways to get there !
If you think about it ,what is the end difference between converting a MAF signal to AFM and then recalibrating the DME or recalibrating the DME to accept a MAF signal ? The answer is close to nothing !
Both routes have their + and - points.
As the next development by Bosch after the AFM for airflow measurement the MAF brings better airflow measurement and a faster response time .
I agree with you 100% that a DME remap is a major step in the search for power .Where a MAF conversion fits in the equation I am not so sure.
From a technical standpoint , maybe around 280bhp . From a desirability view ,who knows !!


All the best

Geoff

NineMeister

Good question - my guess is that the ecu simply runs on the maximum load values in the 3D AFM/rpm "part throttle" table until it sees WOT and then it switches to the full load 2D table values - which cannot possibly be as accurate as a full range MAF set up (nor as accurate as Motec in Alpha-N mode for that matter).

Geoffrey

"As the next development by Bosch after the AFM for airflow measurement the MAF brings better airflow measurement and a faster response time."

We really aren't concerned with airflow (CFM) but rather massflow which is why the MAF is a more accurate measurement of the air. The mass of the airflow will change depending on air temperature and air pressure. Remember, we are looking for a specific air fuel ratio which is the MASS of the air compared to the MASS of the fuel. In addition, we need to understand engine load for ignition timing. Airflow allows a wide range of engine load for a specific airflow measurement which is not ideal.

Lorenfb

"Loren,
I am just trying to understand the thread as much as my limited(very) knowledge will allow. Constructive comments welcome. Flippancy is less well recieved."

Actually, I was really complimenting you on your post as I said it was "well said" and
complete. That's the problem with emails/postings, i.e. mis-communications -------- IT SUCKS!!!!!!!!!!!!!!!!!

Sorry for the misunderstanding.

Lorenfb

"the benefit of the CDI ignition is then compromized" - Geoffrey -

Not true & please explain! Sounds like an "old wives tale".
No guessing allowed. Use equations to show your "belief" in a proof.

"which cannot possibly be as accurate as a full range MAF set up (nor as accurate as Motec in Alpha-N mode for that matter)."

- 9M -

Do what????? Motec alpha-N more accurate than a MAF, please.
If that's what being stated, totally incorrect. A-N just uses the
throttle position as a proxy for load, as it NEVER really "knows"
the load as does sensing mass air flow. The maps are setup
only based on throttle position & RPM, if the throttle position
is set to a different setting than when the maps were defined,
the maps are now NOT setting the AFRs as originally defined
per the dyno settings.

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