Hi chaps general decat question for my MX5, I know this is PassionFORD but I think Mazda have done stuff with Ford before isn't the 323 a rebadged Mk5 Fiesta? Or something like that, anyway...

I bought this decat pipe for er off-road use & thought I'd just swap the cat pipe back when required so they're interchangeable. Was just on my way back though earlier when I saw a mechanic mate who reckons it'd be more trouble than it's worth, cos the power gains would be minimal, overall driveability might be compromised and the ECU over-compensation might destroy the cat when I swap it back - he said that's what happened on his car when he swapped back from a decat (not an MX5) due to the ECU overfuelling & blowing the innards out the back! I thought it'd compensate automatically but he thinks it might need a remap, you can't do that on mine either as it's a s-vt and the budget won't run to an upgraded ECU.

What do you think? Just wanted to go a bit faster for cheap, don't think that's possible on this car! I already changed the air filter...