My new Genmitsu Jinsoku LC-50 Plus claims movement speed of 20,000 mm/min. When I went into the GRBL 1.1 controller to adjust the $110 and $111 values for the X and Y maximum speed, it would not allow me to enter 20,000. For $110, the maximum value I could enter was 16,200. The maximum value for $111 was 15,200. I do not plan on running anything at these speeds but would like to know if there is a way to get a larger value entered into these two parameters.
These values are in the controller built by the manufacturer. These are controlled and stored by the firmware on the controller… if you can’t enter it via a grbl command I think your stuck with the limit.
I think you should ask Genmitsu how they can claim 20,000mm/m when you can’t set the controller to that value.
Good luck
Never mind… I think your problem is with the limits of the machine controller. If you are interfacing with GRBL, you may well have maximum values that are less than the supposed capability of the machine.
If the machine can accept control commands other than standard GRBL, it might be possible to achieve the stated maximums. Of course, that might require a proprietary (and possibly expensive) software interface.
======== previous comment follows… doesn’t really apply, I think ===============
Dumb question… if you are running speeds that fast, shouldn’t you be using mm/sec settings in LightBurn? I don’t know if that will make a difference in performance, but it might be worth a try.
Great question. I am sure they did some fancy math to come up with that value or they did some testing with a different controller. I will ask them none-the-less. I wouldn’t run anything at 20,000 mm/min as the machine is too small to ramp up to that speed and back down in a meaningful way. Just to test the speed, sure. To use for anything real, most likely not.
I bet they came up with that max speed using math and/or a different controller. I wouldn’t run anything that fast anyway as the machine is really too small to get up to that speed and then back down in a practical or meaningful way. For fun and testing the max speed, I would totally do it. 
I have my max values set to $110=16200 and $111=15200 as those are the maximum values the controller would let me set.
You may be able to recover to the original speeds doing a reset. If you try this, I suggest you have a backup of the values in case you need to compare/restore.
$RST=*
They’ve invoked the shade of Pythagoras, then rounded down to a nice-looking number.
The square root of the sum of the squares of the maximum X and Y values you found is … wait for it … 22,214.
So, yeah, it can reach the claimed speed, but only when you clock it along the diagonal of a square with both axes running flat out at their top speeds.
Source: OMTech does exactly the same thing by claiming a 700 mm/s top speed with axes limited to 500 mm/s.
You’re dreaming … lol … they probably dropped it off the 3rd story of their building and it was moving 20000mm/m when it hit the ground 
There are general ways to determine how fast your machine can run. It should be done to determine values within range of your machines ability. If you wish to change this stuff figure out proper values so the machine is working as designed.
These values you are changing are there to protect the machine, which you have effectively negated by modifying these limits.
Having said that, it doesn’t really ‘hurt’ the machine if the fields are moving faster than the motor can respond, but it sounds terrible. This is different than it slamming into the frame at full speed…
You can ‘tune’ it (within controller limits), there are many videos doing that.
I hope you saved the ‘fresh’ factory settings…
How fast it can run is determined by a number of related items, such as mass of the object you’re moving, the acceleration rate and the basic physics of how fast the motors and parts can physically move …
There is always the option of another controller or maybe a firmware upgrade … ?
Having fun is generally the priority with most of these
Take care
I would likely never run the machine anywhere near 20,000 mm/min anyway. And yes, I am having fun with this. 
Very much the priority here.
somewhere is a maximum pulses/sec limit with the arduino, 30,000 ?
the newer grblHAL on faster hardware can well exceed this maximum pulses/sec