You put a portal on the ceiling and then put a portal directly under it. Jump into the floor portal and keep going until high speed. Then put the ceiling portal next to the floor portal and you'll get insane height.
Also how do you do level 35 (or is it 36?). Well the one where you have to get the energy ball through five walls by pressing five buttons.
Kimi wa ne tashika ni ano toki watashi no soba ni ita
Itsudatte itsudatte itsudatte
Sugu yoko de waratteita
Nakushitemo torimodosu kimi wo
I will never leave you