Hitchcocks Forum

I have a Euro IV C5 with that catylitic converter in the bottom of the header pipe. I have attached a picture. Looking down the pipe it seems to be blocking the header pipe by a substantial amount. Has anyone reamed this out? Is it a good thing to do to help the engine perform better or will it just muck up the ECU?

Not a specific answer but I'd expect it'll have an exhaust gas sensor downstream of that. Can't say about an Enfield but most euro 4 vehicles would detect an emmissions fault and at best show a fault light, at worst go into "limp mode".

No there is no sensor downstream. Only sensor in the exhaust is the O2 sensor right near the head and it has nothing to do with the cat.

Our hosts supply a replacement front pipe which does not have a cat. As this is supplied for all C5 from 2009 (including Euro IV) on the understanding that ‘most of these systems will work satisfactory’, logic would suggest that the removal of the cat should not challenge the ECU beyond what it was able to respond to.

Having said that it's recognised that individual engines may respond in some unpredictable ways to these changes of exhaust and so an ECU up-grade may be required. Which suggests that there is no one definitive answer. The effect on performance wouldn’t be clear until it’s possibly too late!!

I can tell you from practical experience that the Hitchcocks single skinned pipe advertised as Euro IV compatible does not provide any performance increase over the standard pipe with the cat on a Euro IV C5. In fact the bike runs better over the whole range with the bog standard exhaust system. I am quessing that the ECU has very little ability to respond to tuning changes.

The EFI models have sensors in the exhaust, throttle body and airbox which send signals to the ECU to make changes to give optimum fuel / air from sea level to 15,000 feet ( highest road in the Himalayas as an example ) If it can make those sort of changes I am sure it will cope with an exhaust change within reason.

The Euro IV C5 Enfields have a very narrow band O2 sensor and ECU response. The bikes sold in India, which are designed as you say, to operate from sea level to extremely altitude do not comply with Euro IV and have a totally different ECU.