The A340 originally had been designed for some PW large diameter wonder engine that never became available. This is why Airbus had to mount four A320 engines instead that were not exactly overpowering it, especially the early A340-200. Given its turbulent history it finally sold not that bad and lived quite some time. However the later A340-600 and -500 were a strange move to counter the 777-300ER fast and dirty. The real bestseller and clear star was the lower profile workhorse A330.