John 37

My STI Hatch has always struggled to pass the MOT test. The engine is forged but otherwise standard. The exhaust is a Milltek in good condition with a cat. A chance comment by my tester that I may have an air leak made me think. My car has a single pipe into the back box. This has 2 outlets that split again into 4 tailpipes for styling purposes. I wondered if the Subaru boxer design produced exhaust pulses that drew air in through the multitude of tailpipes. At last MOT, I held my hands over the 2 tailpipes on one side to increase the gas flow through the other 2 and reduce pulsing effect. From there it was impossible to see the test results but the mechanic said it sailed through.
I'm not saying this will cure all emission problems but it's worth a try.

Matty81

my mechanic friend struggles to get mine through. after a 40min warm up and a couple of runs it finally gets through!. mines a hatch aswell haha

hedgecutter

iTrader: (5)

I can't see how the exhaust could have anything to do with the actual emissions as it's just a conduit ie it doesn't make the emissions of combustion. The mechanic was most likely referring to an inlet air leak.

The Joshua Tree

My JDM 20th Anniversary hatch flew through its MOT last week with no advisories, i asked him how it was on the emissions, he said it was perfect exactly where it should be. The car is totally standard as it left the factory, maybe the JDM ones are more emissions friendlier than the UK 2.5, i don't know if that's the case or not but i guess it could be possible.