No you don't need a check valve...
I just put a turbowerx on a single hellion car today. I mounted it where the stock intercooler pump was. in that general area.
Why would a single Hellion car even need one?
Did he not want to tap into the oil pan, so maybe he is pumping it back into the top of the motor or something instead??
Sounds like a Turbonetic issue to me..
Hope everything works out well for you man, nothing worse than a nice turbo cobra with blue smoke puffing out the back... BEEN THERE DONE THAT
I have my -10 steel line but i think i may use the black cloth style looks nicer. Bought all my fittings, not cheap and i will have pics tomorrow.