My last tank lasted 510kms and i filled up 43ls. This includes a cruise to singleton. However in normal city traffic my tank will only last me around 440km so roughly 10kms per litre and also my fuel light will come on around 8 litres left. For spark plugs i've changed it as soon as on got the car and they are bkr7iex-11 by NGK from jdmyard. If you want to change plugs, make sure you have a spark plugs remover tool cos cause this will make it a lot easier. Or even a spark plug deep socket cos these have a rubber washer in them to help pick up the plug inside the hole.