The Mahindra XUV 3XO ZNG and Tata Nexon iCNG are the only SUVs in the segment to pair a factory-fitted CNG kit with a turbo-petrol engine. Both are offered only with a 6-speed manual gearbox and use a twin-cylinder CNG setup that’s situated under the boot floor. So, if you want to keep running costs in check without giving up the performance of a turbo-petrol engine, which of these two compact SUVs.