^^^THIS^^^
Use the SoftFever (Orca Slicer?) fork of Bambu Studio on GitHub. It has a calibration option on the top menu bar that will greatly assist in dialing in nozzle size for flow, PA, speed… Another thread in here about the 8mm nozzle. IIRC someone was able to increase the flow rate (mm3) and speed and cut the print time 30% or 40%.
Thank you very much. I appreciate it. I will have a look at this. I guess I could just turn up the temperature to make up for the speed and praying for more layer adhesion
you can crank the Max flow mm/3 its quite conversative
You would be better off as Mr.Exocomp stated by increasing the flow mm/3 and speed rather than temps.
Using a calibration would be best but a WAG would be 50% more than the .4mm nozzle to start and see how it does.
I have yet to do mine so I can not give any baselines to start. Logic says the X1C and P1P should be able to do the same speeds on all nozzles, just need to get enough filament through the nozzle on the larger sizes to keep up. An increase in temp may be needed.
Thanks for this. What’s a WAG?
Wild A$$ Guess
I second the suggestion to use OrcaSlicer from SoftFever. If you want to go faster you need it.
If you’re not using I wrote a long a$$ PSA (Public Service Announcement, not as fun a WAG) about it and BL Studio as well as Arachne, another commonly misunderstood item:
https://forum.bambulab.com/t/psa-up-your-game-studio-softfever-orcaslicer-arachne
OrcaSlicer has several Calibrations that will let you max out and fine tune your printer for a .8 nozzle. He put them in proper order on the Calibrations tab at top. Don’t forget to look at his Wiki which explains how to use them, with pictures, it’s in my post.
I usually run a .6 and found after calibrations tests that I could run the Max Volumetric Flow almost three times the default value for PC (polycarbonate) and it tuned other settings for beautiful smooth surfaces as well.
Don’t forget the rule of speed: If you increase speed you must step up the nozzle temp too to help melt the plastic faster and get good layer adhesion. Which means you also must up the fans to cool it for each layer. This stuff gets complex quick! 
That can all be saved as a Filament Profile for future one click access. I name it like this:
Polylite PC Red .6 with the nozzle size so I remember which profile is which.
One other thing to consider. If you really have a need for speed, look into replacing your nozzle with a high flow version called CHT. There’s a long discussion with links here:
https://forum.bambulab.com/t/first-benchy-printed-with-bambu-lab-x1-cht-nozzle
Cheers!
I recently switched over to a 0.8 nozzle and doubled the mm3 rate, and just added 10 degrees to the temp and a job went from 3hrs to 2hrs.
The main problem people have is when they say a 0.8 nozzle is not speeding up the print or even taking longer is usually that they do not adjust the wall count and infill, so print the same model with double as thick walls.
But volumetric flow will limit the possible speed of a 0.8 nozzle quite a bit, and if you really want to push, get one of those aftermarket CHT clone nozzles for high flow. Currently they aren’t available in the right height in a hardened version though, but I guess its just a matter of time till that changes. Gives bout a 35-40% in max flow increase.
User instructions are calling for cutting off 1.2mm(?) of the hot end tube going into the heat sink to get the correct nozzle height.
Making a clean cut on that tube and de-burring it however for most people is outside their skill set.
For larger models I am already hitting the default volumetric flow limits with the 0.4mm nozzle, I doubt going to 0.8 makes much sense with the default hotend, 0.6 makes more sense but only for certain prints.
I guess it depends mostly on what you are printing. If I were to print large parts with the same filament I would calibrate it for flow and temperature with a 0.6mm nozzle and increase inner wall and infill width to match what the hotend is capable of. I tried just bumping temperature and flow and for most of my filaments it didn’t work too well as the finish of the print showed the different flow/temperature difference too much (different matt/shine in places).
There are already nozzles available with the correct length. Just no hardened ones, just brass. Give the aftermarket a few weeks of time and it will find also fitting nozzles as hardened steel.
Yeah, those AliExpress manufacturers are really tuned into the 3D market, and some make incredibly accurate parts often pushing the technology forward faster than the mainstream companies!
Some are real masters at filling a hole a mainstream company missed, or repairing an issue with a particular machine before the makers can.
IIRR they had PEI sheets out before BL did.
And not to forget that often these companies are the ones making parts for the actual manufacturer! The non-compete clauses in Chinese law must have some real holes in them from what I’ve seen.
I am not even sure any such law exists there 
I think it is a “Must Compete” clause.
For faster printing you’d be better off with a clone hot end with a clone CHT brass nozzle installed. Original Bambu is OK for smaller nozzle but on larger sizes hotend melting capability becomes a bottleneck.
Thanks, I’ve been following the long thread about the CHT nozzles (I have some for my Duet CR-10S). Actually was looking on Ali this AM!
My problem is I bought full printheads for .6, .8, and .2 nozzles as well as the parts to make it plug and play (heaters, etc) for the .6 and .8.
My Wife (who is very 3D printing savvy, probably past 40% of the people on here) would not be very happy for me to buy whole new printheads in CHT. Fails the Wife Acceptance Factor
But thanks for the heads up! 
For those reading this not knowing about CHT, read this (Click the Blue Link!):
The good thing about the aftermarket hotend is that you only need a single one and can simply switch the nozzle. So might not be as bad for the WAF as it seems.
Except that now he has BL .2mm, .6mm, and .8mm hot ends (like me) that won’t be used or needed.
Yeah, well my Wife would notice. Without tooting my horn, I’m fairly sharp. She leaves me in the dust. 
Like scary smart.
Yep. Care to buy them?