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911 DME 3.2 Performance Chip Ignition Map Comparison

Stock Chip

Load (%) 1800 2500 4000 5000 6000
10 9 17 23 23 23
20 20 34 38 39 40
30 11 22 26 25 25
60 11 19 25 20 20
WOT - 22 25 23 23

Supplier A

Load (%) 1800 2500 4000 5000 6000
10 9 18 23 23 23
20 21 35 40 41 42
30 13 25 30 28 28
60 16 25 31 26 26
WOT - 26 30 26 27

Supplier B

Load (%) 1800 2500 4000 5000 6000
10 28 28 38 42 42
20 34 40 44 44 44
30 31 34 32 28 28
60 19 28 29 25 26
WOT - 26 28 25 28

Supplier C

Load (%) 1800 2500 4000 5000 6000
10 10 17 28 32 32
20 23 54 53 48 48
30 32 33 38 36 36
60 20 25 28 24 26
WOT - 28 30 24 29

    Notes:

          1. The values shown are degrees advance BTDC as a function of loads & RPMs.
          2. The data set for each chip is a 12 X 12 matrix plus a WOT vector. The selective
              data above indicate where variations exist in the matrices and vectors from the
              stock chip. The data points not shown were basically the same as the stock values.
              The data were determined by using an EPROM editor on a PC which provides
              actual timing advances & fuel enrichments from their respective maps.
          3. The results indicate that all the performance chips kept the fuel maps essentially
              unchanged from the stock '88/'89 911 Carrera. Fuel map changes have little to
              no effect for a stock engine without modifications, e.g. cams, etc., when operating
              closed-loop via the O2 sensor, with the exception of the WOT map, versus changes
              to the timing. Even at WOT, AFR changes in the range of 11 to 13 have a minor
              effect. Typically, a change of one degree in timing, though, will result in about
              a change of three to four HP at the mid to upper RPM range.
          4. The key similarity between all the performance chips is the 'pushed' ignition
              timing maps. The timing maps of these chips have advanced the timing as much
              as 10 degrees over the stock maps to a value of 50 degrees advance BTDC.
              This 50 degree advance value exceeds by more than 10 degrees what Porsche
              techs consider the maximum advance for a 911 engine, irrespective of octane
              levels and fuels available, with a single plug ignition system. Porsche with its Club
              Sport DME did not even 'push' the timing maps, but used the stock '88/'89 maps.
              Additionally, all performance chips increased the rev limit; A - 6920, B - 6840,
              C - 7040, versus the stock chip set to 6520 and the Club Sport set to 6840.
          5. The results indicate that pinging/detonation will occur with performance chips,
              whether audible or sub-audible, because of the excessive timing advances used
              which become more problematic with increasing temperatures & heavy engine loads.
              Furthermore, because of the single spark plug and its location, the early air cooled
              911 engine is more prone to detonation the result of non-stock ignition advances,
              versus a center located spark plug of the later water cooled 996, resulting in long
              term possible engine damage. Also, emission tests may fail NOx because of
              excessive timing advances under certain engine loads/RPMs in addition to idling
              problems, i.e. surging or a high idle. Although the intake air temperature will reduce
              the timing 3 to 4 degrees (maximum change of 5 degrees) at high air temperatures,
              the margin of safety before pinging/detonation is still reduced and problematic.
              Porsche with its knock control ECMs, e.g. 928/964/993, retards the timing up to
              nine degrees from their ideal tuning to protect the engines from detonation,
              which is not possible after ignition tuning a 911 3.2 DME ECM.
          6. The overall results are basically analogous with the re-adjustment of the distributor,
              on engines without an engine management system, to advance the ignition timing
              beyond the stock specification for performance effects, i.e. a more responsive
              feeling engine. The 911 3.2 is basically the same engine as a 911SC with a longer
              stroke (+4.0 mm) and a higher compression ratio (9.5 versus 8.5). Rarely if ever
              is the 911SC ignition advance modified or increased from stock, versus the 911 3.2
              with its higher compression ratio that is commonly 'pushed' beyond stock by a
              'performance' chip.
          7. In summary, engines (911 3.2 Carrera) without a knock control system and because
              of the non-centered spark plug require an ignition map that is conservative, and as such
              performance chips with a 'pushed' timing, i.e. a modified ignition map, should be avoided,
              or engine damage may occur. The stock '87 911 3.2 per the Porsche Spec Book
              produces about 185 HP (217 X .85).
          8. Data indicate that changes in the AFRs from about 11.8 to 14.7 yield only a 3%
              change in torque. "Automotive Handbook - Seventh Edition", Bosch, pg 641, 2007

              "In the areas of interest - near the maximum power point and the minimum fuel
              consumption point - those curves are relatively flat. Even if the system can be
              adjusted to deliver the perfect mixture (just at the point of maximum power),
              the gain promises to be pretty small. There are no huge amounts of horsepower
              to be unlocked there. "Bosch Fuel Injection & Engine Management", Charles O. Probst,
              Chapter 7, pg 7, 1989

              The following dyno graph shows where small ignition timing changes (3-4 degrees)
              resulted in significant changes in torque. The second dyno graph shows where AFR
              changes around the ideal of 12.6 resulted in basically no effect on torque.

                  

                                    

AFM Voltage Output Comparison

  Flap Angle (degrees)   Analog ECM (volts)   Digital ECM (volts)
0 1.70 .25
15 3.20 .55
30 5.00 1.05
60 6.80 2.30
90 7.36 3.45
110 7.58 4.50

    Notes:

          1. The maximum flap angle is 110 degrees.
          2. The analog ECM is L-Jetronic & the digital ECM is Motronic.
          3. The input voltages are; analog ECM AFM = 12.0 volts, digital ECM AFM = 5.00 volts.
          4. V(out) analog ECM AFM = F (sqrt flap angle), V(out) digital ECM AFM = F (flap angle)

MAP Sensor Fuel Injection Pulse Comparison

Manifold Vacuum (psi) Digital ECM (ms) Analog ECM (ms)
0 3.75 7.0/4.5
5 3.30 5.8/4.0
10 2.85 4.2'3.0
15 2.40 3.0/2.3
20 1.95 2.3/1.7
25 1.50 1.7/1.4

    Notes:

          1. The times shown are the injector pulse widths at normal operating temperatures.
          2. The analog ECM times are for a D-Jetronic ECM at low/high RPMs.
          3. The injection time T = T(min) + (T(max) - T(min)) X (1 - MAP / MAP(max)),
              where MAP is the manifold vacuum & MAP(max) is the maximum manifold vacuum.
          4. A manifold vacuum of 14.5 psi = 100 kPA = 1 Bar.

911 3.2 ECM Fuel Quality/Emissions Switch

  Switch Position   Mixture Offset (%)   Timing Offset (degrees)
1 0 0
2 +2 0
3 +4 0
4 -3 0
5 0 -3
6 +2 -3
7 +4 -3
8 -3 -3

Porsche 993 MAF & DME System Data

RPM  MAF (volts) Mass Flow Ignition Timing Load (ms) Pulse (ms)
Idle .80 27 3.5 1.80 3.3
1000 .90 30 13 1.40 2.9
2000 1.05 45 32 1.20 2.3
3000 1.25 64 35 1.10 2.3
4000 1.40 91 38 1.20 2.3

    Notes:

          1. The Mass Flow values are shown in kilograms per hour (kg/h).
          2. The MAF sensor is a hot film type mass air flow sensor.
          3. The Pulse values are the injection pulse width times.
          4. The engine conditions were; fully warm, unloaded, & Lambda = 1.0.
          5. The ignition timing is in degrees advance BTDC.
          6. The data were determined using the Porsche PST2.

Porsche 986/996 MAF & DME System Data

RPM  MAF (volts) Mass Flow Ignition Timing Load (ms) Pulse (ms)
Idle 1.30 15 5.0 1.10 2.6
1000 1.35 20 10 1.20 2.6
2000 1.70 40 23 1.20 2.7
3000 1.90 60 32 1.20 2.7
4000 2.11 80 36 1.20 2.6

    Notes:

          1. The Mass Flow values are shown in kilograms per hour (kg/h).
          2. The MAF sensor is a hot film type mass air flow sensor.
          3. The Pulse values are the injection pulse width times.
          4. The engine conditions were; fully warm, unloaded, & Lambda = 1.0.
          5. The ignition timing is in degrees advance BTDC, with a maximum of less than 40 degrees.
          6. The front two wideband O2 sensors provide a current range of about +/-25 to +/-50 microamps
               for Lambda of about 1.0, and about -1.5 to -2.5 milliamps for a very lean AFR condition.
          7. The data were determined using the Porsche PST2.

 



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