I did a brake test today. when I pushed hard, the rears locked up and the back end started to come round a bit. which way should I turn the bias bar to give it more front end braking?

Screw it towards the front master cylinder... I think thats the left one iirc

(1) start with it screwed towards the front and adjust towards the rear 1 turn at a time.
(2) Road test on dry smooth well surfaced roads at slow speed.
(3) When you reach the adjustment point where both front rear start to lock together back off 1 to 2 turns towards the front -- for SVA give it 3 full turns towards the front.

(4) Repeat test turning wheel slighty as you brake -- then repeat test again gradually building up speed at no point should the rear wheels lock before the front.

(5) For track use in the wet weather 1 turn towards the rear will normally give optimal braking.