Brit car

Not done much night racing but i would say put the camera into manual mode. Set the aperture as wide as it will go. This will get as much light as posible to the camera. Think it's f3.5 on your lens and use the slowest shutter speed you can get away with. It'll be cold so slower shutter speeds will be difficult. Your sheddon pics was 1/80 so aim for that again or slower if you can . 1/50 down to 1/10. It's easier to get longer shutter speeds when your using a shorter focal lenght
The other setting you want to change is the iso. Take this out of auto and set it to 800. This will make the camera more sensitive to light but without too much noise. You could go to iso 1600 but the photos will start to get a bit grainy there. When panning the autofocus may struggle to work properly so set it to spot focus and select the centre point. Then target one of the cars lights. The lights are bright enough to focus on.
This was 1/100, f4.5 iso 800. I couldn't get any slower as i was freezing! The sun was below the horizon at when i took this.
Tempest rally 2011 ford focus wrc by
Micky Photography, on Flickr
You could use a flash but i don't think you'll be close enough to the cars and it freezes the action.
Using my external flash at full power was only just enough 20ft from the car. This was so dark i couldn't see my feet!
Tempest rally 2011 Ford escort by
Micky Photography, on Flickr
The other thing you can try is light trails after it gets really dark.
283/365/2011 Tempest rally light trail by
Micky Photography, on Flickr
Set the camera to manual. Widest apeture. iso to 400 or 800 and shutter speed to 30 seconds. Put the camera on something sturdy or a tripod . ^^^ Camera was on a tree stump. Turn image stabilzation off and change to manual focus. Foucs the camera (live view can help) and start the exposure.
Hope that helps a bit

Don't remember your sheddon pic in here so here it is

