MK4 firmware to MK3 printer  

RE: MK4 firmware to MK3 printer

The hardware (electronics mainboard) is different. That would be a good reason not to try this. 🙂

RE:

No.

8 bit controller on the Mk3.  32 bit controller on the Mk4.  Completely and totally different and incompatible.  

If you want to run Mk4 firmware you will need to get the Mk3.5 upgrade, which includes the new 32 bit controller.

RE: MK4 firmware to MK3 printer

Walter & Patrick, thank you both for your input.  Sure would be nice if some of the features of the new MK4 were in the MK3, such as targeted/object placement pre-printing Z height leveling.

RE:

If you think that makes a big difference time-wise before the printer starts to print, that difference is not very big. The moves and actions before printing starts on both are a bit different. The MK3 heats up the hotend and the bed to the specified temp for the print, then homing, bed calibration and then printing starts. The MK4 heats the nozzle to 170 °C (or cools it down if it has a higher temp at print start), then does the z homing, nozzle cleaning moves on the bed, as soon as the bed has target temp for the print it does the bed calibration, then it heats the hotend to target and starts to print. I have started prints on both almost at the same time and the time until the actual printing started differred only by some seconds, perhaps half a minute. The MK4 prints faster after the first layer, a bit without input shaping and a lot with input shaping, but the time until the start of the actual print is not much different between both.
This is without pre-heating the printers to a specific temperature for the respective process (printing temp on the MK3 and 170 °C nozzle for z homing and bed temp for immediate start of bed calibration on the MK4). But I don't think that with pre-heating the difference would be much more.