arduino with internal oscillator on 1Mhz

i just read 5-6 topics on how to use the internal oscilator

but i am also stuck in something

i can reprogram the fuses with avrdude and a usbtinyisp programmer
so the atmega will run on 8Mhz of the internal or 1Mhz

so far so good

now when get the hex from the blink code and upload it to arduino(without the bootloade)

and the 1sec is actualy 2sec (on 8Mhz) or 16(on 1Mhz)

ok i was expecting that

now i am changing olny that from the boards.txt file

atmega328.build.f_cpu=16000000L
to
atmega328.build.f_cpu=8000000L or atmega328.build.f_cpu=1000000L

then i remake the hex and upload it again to arduino

and the led blinks normanly in 1sec

but when i am changing the

delay(1000) in the code with the
delayMicroseconds (1000000)

it dosent work

so how can we fix that?

thanks a lot

*i dont care for bootloader - i dont use it anymore