Hi I'm looking to change my gearbox on the Vauxhall c20 let turbo I'm running the standard type 9 and am running 300bhp at the wheels so I'm looking at gearbox options and the rx8 6 speed keeps coming up so my question is would it be any good on the turbo engine and would it fit straight into the tunnel

You will need to find out the sizes of it and just get under car and check imo.

Will depend on your engine position,and shape size of tunnel.

I know the Rx8 box is longer than a T5 cosworth box,so I would guess it will be longer than a type9.

A m8 tried to fit one to his V8 westfield, but gave up once he realised how much work was involved on the tunnel to get the box in.

The RX8 box is same length as type9 but considerably larger. Output spline is the same.
It might be on it's limit at 300hp.