tuning programmable engine management systems

[scarceller]

Originally Posted by 911st

Sal, You are a great resource on Motronics, thank you.

So are the two axis on the map RPM and AFM voltage or postion? Or are you saying the second axis somthing other than AFM voltage?

I understand some type of correction factors that take the active cell and modify it for O2, temp, etc. But is sounds like there is somthing else going to degermin the second axis???

Not getting it I guess.

If the cell value is just RPM by AFM voltage I can understand how we could set a line of cells that represent cruse load at cach RPM level. Then the cells just past that line where the AFM voltage is a bit higher could be a more aggressive settings. Then again eventually approaching values to achive max TQ levels as on the WOT map. How fast the cell values approach aggressive values would have an impact on part throtle response.

The 'load' Axis is not simply AFM signal. Let's try another way to explain.

Lets say Air Flow is a value of 0 to 100, 0 being no air (AFM door closed) and 100 being door fully opened.

So we can have an air flow of 50 (door 50% opened) under many different RPM values.
For example:
- it could be 50% open at 3000RPMs under light load
- or 50% at 2000RPMs under moderate load
- or 50% at 5000RPMs under decel condition

This is why you can't just drop the AFM signal into the load axis - it must be compensated along with engine speed (RPM). The AFM door being at a given position does not alone indicate load. But if you combine the door position with RPM you can deduce load.

Also think of it this way: for a given RPM say 3000RPMs the AFM signal can vary by a significant amount based on throttle angle. At lo-load the door could be 50% open but at WOT fully loaded with a Load dyno at 3000RPMs the door could be 90% or more opened. Then on decel down a steep hill you could maintain same speed and RPM of 3000 but throttle would be closed and door only 25% open. As you can see the AFM signal can vary by 75% even though RPM has not changed.

[scarceller]

Originally Posted by jpnovak

Sal, thank you for the ignition maps.

Does the Motronic WOT ignition map differ much from the high-load sites on the part throttle map?

You got it, the hi-load row in the PT Ign map does indeed match very closely with the WOT ign map. They do this so the transition from the PT ign map to the WOT ign map goes smoothly. Most chips I've seen have these set very close or the same.

Go look at the prior post with the Euro Ign Map you'll see this is the case.

Great question.

[jpnovak]

Thank you Sal. I assumed this was the case. All the transitions should be smooth.

I am getting ready to integrate spark into my EFI system and have been curious bout how much advance one could run at medium loads. I am running a twin-plug system and think I can start the map process by scaling the single-plug values down. I will have a knock sensor and use this as feedback for maximizing advance at different load cells.

So far, the fuel tuning has been very straightforward. I will wait to say the same after experimenting with spark.

[911st]

Sal,

So the table is RPM by Load ("Throttle %"?).

Load is derived from the expected Air Flow (AFM V?) against some type of base map or formula.

If the base map or formula perfectly fit the motor all the cells would be the same number (128?) and / or there would be no need for the Fuel Trim table.

Also, if one piloted cruse at each rpm point, it should stay close to one of the Throttle Percentage lines through the RPM range (something near 26%?).

The numbers in the cells are used to "correct" or "adjust" what is expected from the base map or formula to fit the motor. Thus "trim" the base map or formula cell.

Am I getting warmer?

Big Thanks.

[scarceller]

Originally Posted by jpnovak

Thank you Sal. I assumed this was the case. All the transitions should be smooth.

I am getting ready to integrate spark into my EFI system and have been curious bout how much advance one could run at medium loads. I am running a twin-plug system and think I can start the map process by scaling the single-plug values down. I will have a knock sensor and use this as feedback for maximizing advance at different load cells.

So far, the fuel tuning has been very straightforward. I will wait to say the same after experimenting with spark.

Jamie, I think the 95 993 car is twin plug car would those ignition maps help?

[scarceller]

Originally Posted by 911st

Sal,

So the table is RPM by Load ("Throttle %"?).

Load is derived from the expected Air Flow (AFM V?) against some type of base map or formula.

If the base map or formula perfectly fit the motor all the cells would be the same number (128?) and / or there would be no need for the Fuel Trim table.

Also, if one piloted cruse at each rpm point, it should stay close to one of the Throttle Percentage lines through the RPM range (something near 26%?).

The numbers in the cells are used to "correct" or "adjust" what is expected from the base map or formula to fit the motor. Thus "trim" the base map or formula cell.

Am I getting warmer?

Big Thanks.

YES! you got it. At cruise on level ground you are generally in the 2nd or 3rd row across all RPMs.

And again YES if everything was perfect then all cells would be 128. But Bosch designed this system to fit many different setups and be very adjustable so that's why the trim tables.

You have the basic understanding for these maps!

BTW - if someone knows the exact formula for LOAD I'd love to have it. I have seen references to the formula made and it does seem to be some sort of AFM signal divided by RPM.

[911st]

Originally Posted by scarceller

YES! you got it. At cruise on level ground you are generally in the 2nd or 3rd row across all RPMs.

And again YES if everything was perfect then all cells would be 128. But Bosch designed this system to fit many different setups and be very adjustable so that's why the trim tables.

You have the basic understanding for these maps!

BTW - if someone knows the exact formula for LOAD I'd love to have it. I have seen references to the formula made and it does seem to be some sort of AFM signal divided by RPM.

Sal,

Again, thank you for taking the time to teach me/us.

From what you are saying it sounds like the heart of the fuel deliver system then is basically a math formula to compute the quality of fuel needed for any size and performance level of motor relative to RPM, load, injector size, fuel pressure... But that is just a guess.

Might start with something like ((motor capacity / number of cylinder) x (RPM/2) x (VE))/target A/F ... and have a bunch of other variables that can be changed to fit any make up of motor.

This formula then computes the expected duty cycle at each point of operation.

Then it sounds like the Trim Table modifies the theoretical fuel delivery to the unique specifics of a motor.

[jpnovak]

Yes, the 993 spark maps would help a lot. More compression and twin-plug in the 3.6. What I need to figure out is how the spark map relates to peak torque rpm and shift accordingly to the cam choice. My cam should have a peak torque approximately 800 rpm higher than a 964 or 993 cam.

I am running megaquirt. You have the choice of specifying the number of squirts per injection cycle as a multiple of the number of cylinders. For a 911 this can be 6,3,2,or 1. I use six smaller injections compared with one large batch fire. I have my injectors wired with alternating squirts such that 162 and 435 are grouped together. This represents the two rotations of the crank.

MS fueling is based upon an algorithm that determines the pulse width of injection (ms) based upon multiple constants.

PW = REQ_FUEL * VE * MAP * E + accel + Injector_open_time

Several of these values are constants. Req_fuel and the open time are injector constants dependent on the actual injector (flow rate and impedance) MAP is read by the engine, VE is the fuel trim number in the load vs rpm map. Accel is the enrichment from changing throttle positions. Accel can add or subtract fuel. The correction factor takes into account pressure, temperature, closed-loop O2 and warmup corrections.

E = gamma_Enrich = (Warmup/100) * (O2_Closed Loop/100) * (AirCorr/100) * (BaroCorr/100)


Megasquirt is very capable. Currently with the exception of sequential it has everything one could want including the rpm activated switches and triggers. ONe day I will install a varioram top section on top of small ITBs and control it all with MS for the best of both worlds.

Prototypes of the sequential exist and are being beta-tested. Target delivery if later in the spring. I have considered the upgrade but probably will not since my car drives great at low rpm and emissions are not an issue. Its fantastic at high rpms.

[scarceller]

Jamie,

Here are the 95 993 ignition and fuel maps. The theory that twin plug needs less advance is sort of out the window if you look at the 993 Ign maps. In the PT Ign Map it does seem to back off on ignition for part load as compared to the 86 Euro. But the 993 WOT Ign map pushes into the 30BTDC and one wild spot is at 2480RPMs it pushes 67BTDC! I keep looking at it saying it must be wrong, but it appears to be by design. Any idea why push so much advance at WOT 2500RPMs?

EDIT - EDIT - EDIT - do not trust these maps! they are likely not correct!

95 993 Ign Maps
EDIT: This map was wrong I removed it, see post below for correct map.

95 993 Fuel Maps

[psalt]

Sal,

The 67 BTDC must be an error. There are plently of threads on twin plug ignition timing to read. Most published info suggests that you need 7-10 degree less max timing for optimum power with twin plugs. However, if you look at the ignition timing curves from the 911SC to the 993, this is not what the factory did. The 993 curve I saw showed a max advance above the 26 BTDC max used in almost all cases. Up until the 993, it almost looks like Porsche was married to a 26 BTDC max and altered the compression ratio to suit the fuel spec for different markets. Compression went from 8.5 to 9.8 to 10.3 to 11.3.

[scarceller]

Originally Posted by psalt

Sal,

The 67 BTDC must be an error. There are plently of threads on twin plug ignition timing to read. Most published info suggests that you need 7-10 degree less max timing for optimum power with twin plugs. However, if you look at the ignition timing curves from the 911SC to the 993, this is not what the factory did. The 993 curve I saw showed a max advance above the 26 BTDC max used in almost all cases. Up until the 993, it almost looks like Porsche was married to a 26 BTDC max and altered the compression ratio to suit the fuel spec for different markets. Compression went from 8.5 to 9.8 to 10.3 to 11.3.

Paul,

It could be the chip bin I have if faulty. But if you look at the rest of the WOT timing it shows 30BTDC after 5500RPMs.

I'll double check the chip map by hand with a hex editor to see if those numbers make sense.

[jpnovak]

These curves are most helpful. Maybe it has to do with the large jump in Fuel trim at WOT between 2000 and 2480. Could it be compensation for a low-speed acceleration event based upon timing and not fuel enrichment.

I am sure that some will not share their information and I understand the reason why but I will ask the question anyway. AFtermarket tuning chips make changes to the fuel and ignition maps. In what areas are the factory specifications too conservative? Where are the areas that need improvement and how much can you improve safely? These can be approximations without specific numbers. One might say that after peak torque the engine is too lean(or rich) or that the timing in this area is too advanced for peak output. I realize that once the fuel trim is changed that timing should be altered to take advantage of the increased (or decreased) AFR.

I am currently running a twin-plug distributor. I run 12 deg at 1000 and max of 27 coming on at 4000. This is a converted SC distributor. It runs well but I think I can gain some smoothness for more lean cruise.

I have been reading the book "Internal Combustion Engine Fundamentals" by John B Heywood. There is some very good information regarding spark curves in there. I will summarize once I finish digesting.

Jamie

[psalt]

Hello Jamie,

OEM's are conservative because their product has a warrantee. Engine failure recalls are expensive and embarrassing. So ignition timing curves have less advance and fuel tables are too rich at high load to provide a margin of safety. An air cooled engine needs a wider margin of safety because the temperatures can vary more than a watercooled engine. Aftermarket tuners can take more risk with your engine. Higher octane fuel than the factory spec can balance this risk.

[911st]

Just a though, the 993 has a knock sensor to pull back timing depending on the fuel in the market is was sold. With our fuel, we may not be seeing those numbers in real live.

[scarceller]

Just looked at the 993 chip bin with a hex editor to be sure something was not wrong with graphical editor I use. And the ignition at 2480RPMs does indeed take a wild jump in the raw map. The hex value is a '0x74' or 116 decimal and if I apply the ignition formula to this value it comes out to be 67BTDC.

Could be that I have a faulty bin file but I doubt it.

[911st]

Could that be built in by the Porsche to test the knock sensor?

[psalt]

Sal,

Some of the other numbers in that map look fishy to me. Part throttle timing numbers should not be lower than the WOT map at the same rpm. Did the 993 have a full range TPS and do acceleration enrichment based on TPS ?

According to this map, the highest compression, twin plug engine had the most WOT ignition timing....(3.0-3.6) They would not go to 30 BTDC, even with a knock sensor, unless output was higher.

[scarceller]

Originally Posted by psalt

Sal,

Some of the other numbers in that map look fishy to me. Part throttle timing numbers should not be lower than the WOT map at the same rpm. Did the 993 have a full range TPS and do acceleration enrichment based on TPS ?

According to this map, the highest compression, twin plug engine had the most WOT ignition timing....(3.0-3.6) They would not go to 30 BTDC, even with a knock sensor, unless output was higher.

Paul,

I know very little about the 993 cars, I just had the chip bin and know howto find the maps but that's about it. I'd just be guessing.

[Eric86Red911]

Originally Posted by psalt

... Did the 993 have a full range TPS and do acceleration enrichment based on TPS ?....

993 does have a full-range TPS that feeds into the ECU (I run that signal to my data logger...). Dunno how it's used since I'm no tuner.

Great thread. I run a protomotive stage 1 tt on my 1995 993, so I'm fascinated. I'd love to find a way to custom tune myself.

[scarceller]

Something does not makes sense with the 993 WOT ignition.

Here is another site showing the 964 and 993 WOT ign side by side:
http://911chips.com/ignition.htm
Then scroll to bottom
I trust the info on this site.