How to solve burnt blobs on Prusa MK3S (PETG)?
I saw PETG printed at 100 mm/s, but 150! That's a lot.

One solution to avoid blobs may be to limit the maximum speed to a value you can actually achieve with reliable results.

Simple test to find your machine limits (each combination filament brand + nozzle + temperature has a different value): extrude filament in the air at increasing speeds, see how the flow changes, and when you see more than 5% decrease, that's it.


M83
mark the filament as if you were calibrating the E steps
calculate filament speed: speed = volum/s / filament surface * 60 = mm^3/s * 25 (this factor is valid for 1.75 mm filament)
set extrusion speed for 2 mm^3/s: G1 F50
extrude 50 mm: G1 E50
measure actual length extruded
repeat 2.-6. but increase the speed by 2 mm^3/s each time: 2, 4, 6, 8, 10, 12, ...
at a certain speed you will see that the actual filament length starts to decrease. When you see that the underextrusion reaches 5-10% (depending how much underextrusion you accept), write down that volumetric speed (mm^3/s) somewhere, it's your limit for THAT filament + THAT nozzle + THAT temperature
Either a) calculate the max print speed = volumetric speed / layer height / line width or b) set the maximum volumetric flow rate in the slicing software so that the speed will be automatically capped taking into account layer height and line width. Prusaslicer allows to set that in the "Print" or in "Filament" settings, I recommend it for "Filament" settings, since it's a filament-dependent parameter.


Example data from CNC Kitchen:



You can increase the max print speed, at the price of a little loss of quality around edges, if you calibrate the E steps at a speed corresponding to 2-3% underextrusion (alternative: to the speed of outer perimeters).

This way you know that when you print slower than that (uncommon... typically only sharp corners and small perimeters) you'll get up to 2-3% overextrusion, and you extend by 2-3% the maximum print speed, since your max speed is the one where you get 5-10% underextrusion compared to your E steps calibration speed.