Jfrahm

The problem would be if you are in a cell in the DME that is assumed to be at a light load (lots of advance) and you are actually under some load. This is even worse news if your injectors are oversized for your application, in that case you scale your operating range back, reducing the number of cells the car operates in, and probably never really getting into the full throttle high load parts of the maps (resulting in too much spark advance across the board?)

If the injectors deliver 37% more fuel than stock, then the DME is fooled into thinking the engine is making (roughly) that much less HP. If you are accellerating briskly using 130HP the DME might think you are only using 90 HP. Not a huge deal but again it's probably a lot better to not be hitting the knock sensor all the time. These ECU's are not going to adapt an optimal timing map.
I would think the off-boost operation would be the worst since an engine with a big turbo is still a weezy little low compression 2.5l off boost, and the DME would have some funny ideas about how much power it was producing and where the timing should be if it had large injectors and a scaled back air signal.

And if you have overlarge injectors (perhaps bought with more mods in mind) they might deliver almost twice the fuel as stock. If you are only making 350HP with them you have left maybe 1/3 of the stock maps unused, and the load factor would be off a good bit.

-Joel.

jimbo1111

Jfrahm I will leave you with this thought. If the fuel table lines up properly why wouldn't the timing. They are both relative. Are they not?
I'm not the first to do this or the last. LR, HR, SFR and many more have used this in the past with great success. The bottom line is that it works. I'm not here to get into a pissing match with anyone. I just replied to a lister looking for help on his HR stage 3 maf.
What ever works for you is great. This just happens to work fine for me. See you at the dyno.

Lorenfb

"Both methods work similar. Except with your method I have to buy a chip. With mine I don't. I could use the extra money I saved on a nice exhaust and know nobody has me by the ***** when it comes time to upgrade." - jimbo1111 -

Not really, it's kinda Mickey Mouse and you never really get the optimum torque curve over the
full load range. Remember, the AFM only provides the DME a useable input to 60% load,
after that no more data. So, after the 60% load translation, the MAF is basically
uncalibrated to the actual load. The DME has to use the WOT map.

But then again, whatever makes you happy.

Tomas L

I'm quite sure that I will not convince Jimbo with this so I'm writing this just to prevent others from ending up in trouble after following his advice.
Jfrahm already said most of this but here it is again.
The DME calculates load (cylinder filling) from the AFM signal and rpm.
If you change flow meter this calculation will not be correct.
First of all, the chance of finding a MAF that has the same shape of the flow/volt curve as the AFM is very small. Even if the max flow value is 37% larger for the MAF, the difference is not 37% over the entire range.
This is a problem you can live with, it will not be an optimum situation but with a little tweaking of the maps you can get by.
Then comes the other problem. Lets say that you have a MAF that really gives 37% more flow over the entire volt range. The calculated load will then be 37% smaller than what Porsche (or the chip tuner) anticipated when they made the fuel and ignition maps.
For the PT fuel map this will not be that bad since the map just contains a correction factor (a sort of lambda value), you will be a little of but if you use 37% larger injectors you will get by reasonably.
The ignition timing is a different story. The values in the map are not correction factors in the same way that the fuel values are. Here they are real timing values and if you pick the wrong value you will end up with wrong ignition advance. If you look at the timing map, lets say that you have airflow that corresponds to 24% load at 1440 rpm then your ignition will be 21.2°. If you switch to a MAF that will give you 37% more flow then instead of 24% load the DME will end up with 18% which corresponds to 29.1° ignition advance. Almost 8° difference and I'm sure there are places in the map where the difference is bigger.
I'm quite sure that aftermarket chip vendors that use this method will remap the ignition values (and the fuel map) for the change in load.

AFAIK this is not correct. The DME switches to the WOT map at 66° TPS angle but the AFM signal is still used for fuel flow calculations.

Tomas

Lorenfb

"AFAIK this is not correct. The DME switches to the WOT map at 66° TPS angle but the AFM signal is still used for fuel flow calculations."

Nope!

First, the 944 doesn't use a TPS as defined by most automotive electronics.
It uses an idle switch & a WOT switch. As such, the DME DOESN'T ever know the throttle
position other than at idle or WOT. So let's not use TPS.

Once the the DME senses > 60% load (max AFM output & WOT switch) it switches to the WOT map.
It DOESN'T/CAN'T be using two maps @ once. That's one of the benefits of the MAF is that
it provides more overall air intake or engine load info beyond the 60% limitation.

The max. injection time of 16ms results from the max. AFM voltage of about 3.5 volts
(about 70% of max 5.0 volts AFM input), i.e. 20ms being the max for ANY engine @ 6000 RPMs.
Beyond the 60% load value from the AFM, the AFM provides NO additional load info for the DME.

The link posted above, of the ignition map, indicates the max load info @55% &
a separate WOT map. That fully clarifies the issue & the AFM is not used as an offset
value to the WOT map. Additionally, you need to open an AFM and check its' output
as a function of load if you question your own info. Furthermore, that's why the AFRs have
to be closely monitored beyond 60% load & adjusted for mods since there's no load info
for the DME to utilize.

fast951

944 & 951 TPS are different.. 944's is Idle & WOT... 951's is a 0-5V, so TPS angle is available..

AFM or MAF signal is used under WOT for fuel calibration... It's still used in the formula to determine injector duty cycle... The AFM or MAF signals can be altered (with a PB) to lean or richen the mixture.

Tom M'Guinn

Great discussion. Keep it coming. Just as a point of reference, the TPS on the does indeed have a 0-5volt signal indicating how open the throttle is, along with the idle switch. I log the signal with my wideband, so can confirm it's there.

TT

The DME knows three throttle states: idle, wot, and part throttle. That is all it needs. There is also the idle adjustment state of idle/wot together, but that is only an adjustment state that fixes the idle control valve at a specific duty cycle.

Nope!

When the KLR detects that the throttle has exceeded 65 degrees open angle, it then drives the WOT signal to the DME. Then and only then does the DME use the WOT ignition/fuel maps. If it never gets the WOT signal and the TPS is off idle, the DME will use the part throttle maps regardless of air flow.

The air meter input (VAF or MAF) is always used in the calculation for fuel regardless of the TPS setting. The maps are just modifiers to adjust the final fuel value based upon the lookup value from the appropriate maps. There are limit values in the stock chips that will clip the calculated fuel values even if the meter is not the limiting factor.

As Tomas has posted in other threads here, the DME load value is related to intake manifold pressure. The percentage values on the right side of the part throttle map in that picture has no meaning.

Lorenfb

"944 & 951 TPS are different.. 944's is Idle & WOT... 951's is a 0-5V, so TPS angle is available.."

Not on my diagrams!

The 944 Turbo (075 35 pin box) just has an idle (pin 2) & a WOT function (pin 3). The KLR has a true TPS (pins 21, 22, 23). The 944S (55 pin box) has just an idle (pin 52) & a WOT (pin 53).

Yes, there's an in between state, but this operation is not a true TPS. A true TPS
would allow a virtual load input to a DME unit & not require an AFM/MAF element.
The 968 used a true TPS element (pin 53).

Bottomline: The 944/944S DME NEVER gets a true TPS signal, just gets SWITCHED to WOT by the KLR
in the case of the 944 Turbo.

"As Tomas has posted in other threads here, the DME load value is related to intake manifold pressure."

Indirectly! Load is purely a function of air flow or air mass flow as used by the Porsche DME.
Example: An engine can have a low intake vacuum under heavy load & also a low intake vacuum
under light load (bad rings or valves). This was the problem with the old Bosch D-Jetronic system
with its' use of a MAP sensor.

TT

The 944/951 basically only indicates three states of the throttle position. Sounds like a throttle position sensor to me, even if it doesn't give exact position. Again, the 944/951 Motronic knows three throttle states: idle, wot, and part throttle. That is all it needs.

Sorry! Directly!

Motronic load is a function of air flow/rpm, not just flow. Work the numbers. Include air temp and you can get pressure. With the turbo it starts to deviate under boost since the DME measures the air temp at the VAF (or the MAF is indicating air mass based on the air temp at the MAF) and does not know the intake manifold temp which is modified by the turbo and intercooler efficiencies.

Yes and the VAF/MAF will measure the difference in air flow in each case. Add in rpm and you get load, add in air temp and you can derive pressure. Hell, add in the intake manifold temp and engine displacement and you can derive Ve.

The best thing is that if a MAF indicates that you have x Kg/s of air flow and you want a 14.7:1 AFR, then you just need to add fuel at a rate of x/14.7 Kg/s. No need to derive Ve, just add fuel. That is why Bosch switched to volume/mass metering devices and still use them today. The main drawback is that intake leaks will lead to errors in the VAF/MAF measurements and the engine running lean.

Again, this stuff has been hashed out many times by many different people here on the list.

Lorenfb

"The 944/951 basically only indicates three states of the throttle position."

The middle state provides NO useful throttle info (no actual angle) other than not
at idle or WOT, i.e. it's basically useless.

"Yes and the VAF/MAF will measure the difference in air flow in each case. Add in rpm and you get load,"

RPM doesn't determine the load. It determines a point on the load map. Load is a function
of an independent variable, e.g. 0-5 volt sensor. When combined with RPM, it determines a point on
a three dimensional fuel/ignition map. Example; climbing a hill @ 4000 RPMs & cruising @ 4000 RPMs, same RPM two different loads.

Methods of determining engine load:

1. MAP - manifold absolute pressure sensor, marginal
2. AFM with air temp, not bad
3. MAF, the best
4. TPS combined with RPM, alpha-N fuel injection system
a proxy for the real load; simple & great for race, & non-emission sensitive apps

TT

No. Part throttle is a state. If you don't believe that, then you will never understand 944/951 Motronic engine management.

Part throttle is where a street car spends 80-90% of its time. It is cruising down the highway. It is that period between idle - WOT and WOT - idle transitions.

Again speaking about Motronic. Load is airflow/rpm. If you don't believe me, go google Conforti, Knighton, etc. all the others who have delved into this stuff for the past decade or more.

Since load is related to pressure, then the part throttle table is basically a pressure vs rpm table just like many engine management systems.

alpha-n - PITA for a street car.

MAP does measure load directly.

AFM/MAF cannot indicate load unless you divide it by RPM. If you don't believe that, then determine this:

An engine at 3000 rpm, air flow is 200 scfm.
Same engine at 6000 rpm, air flow is 200 scfm.

With a MAP sensor would the pressure (aka load) be greater at 3000 rpm or 6000 rpm.

If load is air flow only, then the pressure would have to be same since according to you the air flow is the same at the two rpms.

Do the math.

Lorenfb

"No. You're basically clueless." - TT -

Now it starts. Can't discuss the issue, so let's attack the messenger. Real Good!

Load is a measure of work. Torque is work. Therefore load is a measure of torque
being produced. Rate(RPMs) of work/torque is energy is horsepower.

Again:

Example; climbing a hill @ 4000 RPMs & cruising @ 4000 RPMs, same RPM two different loads.
Climbing a hill requires more torque @ 4000 RPMs than cruising @ 4000 RPMs, thus more
load on engine but same RPM. The greater load (more torque) required more
HP to climb at the same RPMs.

HP = Torque X RPM = Load X RPM

no engine load = no engine torque

Load(hill) X 4000 = HP (hill) > Load(cruise) X 4000 = HP(cruise)

Load(torque) determines charge (energy) input (fuel + MAF) for combustion.
RPM determines rate of charge input. Therefore, load(MAF or a proxy) and RPM
are independent variables yielding an energy output (horsepower).

daniel951

there is no need to start another fight in another thread. chill out this is all learning experience for everyone

Lorenfb

"there is no need to start another fight in another thread" - daniel951 -

Please direct the comments to the proper source.

By-the-way, this in Rennlist & not the "other" forum where slams & name calling
are common place. If you disagree, then present an objective rebutal.