10-02-2015, 01:02 PM
its not "backpressure" its flow, for a given gas speed you need a certain flow, get it wrong and yes you create 'backpressure" be that from too large a pipe which causes gas to stop dead, or from a small bore throttling it.
need a part number? http://public.servicebox.peugeot.com/ and http://service.citroen.com/ will sort you out.