Optimum diameter for exhaust

[306rhys]

the most important bit is the collector and downpipe.. it needs to be larger, 2.5 at least, 3 inch preferable, this should then run into at least 2.5 and then you can taper down when moving away from the exhaust to a free flowing 2 inch (minimum) as the gas pressure will have dropped considerably as it moves away from the exhaust.. i would want to be at least 2.5 to where the cat was orignally however..

I contacted the suppliers of the Hoffman down pipe and they say that it's identical diameter to the oem one which is 2.25", right? Will have a browse round and see where I can get one made up