vitz should give good performance on CNG run, xli engine is not used in 1.3L vitz as far as i know. xli's 2nz-fe, 1.3l vitz' 2sz-fe(~85hp) while 1.0L vitz' 1kr-fe(~70hp). anyways, compression ratio (11:1 & 10.5:1) of these engines is much better than other 1.0L engines.e.g. cultus' (9.5:1) and exclusive's(9.3:1), not to mention alto's (8.8:1), making cng run good and economical. the only car running economical with less comp ratio is city idsi(8.8:1) but it has got 2 spark plugs/cyl so compensation is done there.