Looks like I may have done it.
Instead of using the inbuilt ACCEL G function I created a maths Chanel called ACCEL = 'Accel G'*9.80665. This converts the Accel G into acceleration m/sec˛, then I smoothed it to 100.
The result is what I'm looking for, I may play around with the smoothing but it is looking promising.
What it does show is at Sydney Motorsport park the blue (2017) was accelerating faster than red (2015) at the same speed.