If I am correct, Marina pit is located at grid F16, see link:
http://www.singaporegp.sg/ticket/pdf/2011_circuit_park_map.pdf
It's a straight track.
If you can go to the fence, you can try with 18-55.
I believe the cars will keep to the right of the track b4 making the left turn at grid E16. Chances of getting closer shots are good.
Well, you may also bring along the 55-300 for max reach & close up shots. However, a fast lens like f2.8 will help.
Using TAV setting may help since apecture & shutter are preset, only varies is the ISO.
