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Injection timing.

Practical Diesel Tuning

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I am wondering if there are any formulas for adjusting injection timing based on nozzle size? I swapped nozzles on my commuter and everything seems happy. I just would like to be able to calculate to see if my timing maps are correct or if I have some room to add more. I understand it's based on fueling and rpm so that's what makes me curious if there is a formula that would work based on nozzle size. The method that i am using is my new nozzle size .231 divided by my original nozzle size .184 then multiplying that by my original timing which was 15.6* and coming out with 19.5*. Does this method work for injection timing? Or are there any other methods to go about calculating injection timing based off nozzle size?




Most timing maps are built on the dyno using MBT (mean best torque) data. Basically the timing will be varied until MBT is found, from there the timing number may be trimmed for any number of reasons - NVH, emissions, cylinder pressure ceiling, etc. I don't know of any mathematical expressions commonly used to find MBT. What I can tell your average SOTP (seat of the pants) tuner is that optimal timing is usually within a couple/few degrees of NVH (noise vibration harshness) becoming objectionable.

Example: I bump timing up to 7* at a given load/RPM and the engine becomes decidedly louder, I go back to 5 and it quiets down, then I go to zero and it hazes and runs high EGTs. Stick with 5*. Simple but effective if you don't have a dyno.

Hope this helps,



That makes sense. Thank you for the explanation. Your knowledge is appreciated.


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