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calculating master fuel


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i tried to calculate a master fuel for the basic fuel.

so for a 1000ccm injector (1 injector per port) and 3.6l 6 cyl engine i calculated for 100kpa and 100% ve a maste pulse width of 3.9.

Makes that any sence? How do you figure out your master quantity?



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What injectors? Bosch ID1000s?

This is the totally wrong way to do it im sure, but I have ID2000s and used a master of 7ms and 5% (7.35ms) trim on a 2.5 liter 4cylusing 48PSI (330kPa) base pressure

That is .625L per cylinder. You are at .6 liter per cylinder

I would say that for you, using a 3ms master with 20% (3.6ms)  Trim would be close. Smarter people will comment after me, but if you are just looking to see if you can get it to idle, try that. If you want to play it safe, bump up the fuel a little bit.

Better yet, talk to your tuner.

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Hi Philipp,

The calculation for working out a master fuel number would be possible, but complex.

As Levon and yourself noted, factors to include in the calculation would include:

  • Fuel Pressure
  • Cylinder Volume
  • Injector flow rate
  • Atmospheric Pressure
  • Engine Volumetric Efficiency
  • Density and temperature of the air
  • Required Inj PW

Most tuners know from experience on similar setups what a suitable master fuel number is. You are better to start with a number that is too high than too low. Using a wide-band oxygen sensor and monitoring the AFR while you make adjustments would be a good start. The aim is to have middle values in your fuel table with a value of 50. 


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yeah - i will start with the M50b25 base map and a master fuel of 4

(my engine config 1000 injectors and 3.6L)

Then I will try to adjust the fuel map via TPS sensor and no boost and then go to the 4d fuel  table and adjust the fuel and ignition with the map signal.

which maximum ignition angle would you recommend to start with to be safe even with 1.5bar? 20°?



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