Hi 

I just finished a new build, the fc is a Speedybee F405 V4.

I'm in DShot300 and the cpu charge is around 45%. I read that It should be more like 20%.

If i set in DShot600 it back down to 300 after reboot. The gyro is at 8.0khz and the pid loop at 4.00khz.
I'm pretty newb for the BF tuning and I'm not sur to use the right setup. 

Thank for few tips.

At 45%, you should be fine. It appears that 4.3 and newer BF calculate Cpu load higher than pass version.

Details about the changes to the CPU calculation in Betaflight 4.3.x onwards is detailed in the Betaflight5 4.3 Tuning Notes at the link below. Just search that web page for "CPU" and you will see the relevant information...

https://betaflight.com/docs/tuning/4.3-Tuning-Notes

Oscar also makes reference to the same in his Betaflight 4.3 article (HERE)...

Oscar Liang Wrote:CPU % Too hight?!

In Betaflight 4.3, the devs have changed the scale of CPU %. Before the maximum we recommend people to run is about 50-60%, but now they have reduced the scale, and it would still be safe to run at 80-85% CPU load.

Ok thank
I also learn that for F4 board BF lock the setup at 4khz and DShot300 because of somes problem who might appear at 8khz/DShot600.