O.K.
These so called "Experts" sold me some "Performance" spark plugs for a Honda engined Rover 827 Sterling.
This engine would never miss a beat, you would rest your hand on it and feel every piston firing every time:
"Specially Developed Performance Plugs"
Until I put in these plugs, basically their performance plugs randomly select one cylinder for misfire, which in effect gave me a 5 cylinder Rover 822 or thereabouts.
Hardly an increase in performance. Went back there and they gave me another set which were worse. In the end put my old Unipart ones (Nippon Denso) back in and gave up.
"Performance Airfilters that give you 10 - 20 bhp"
These performance air filters and their dodgy brackets may give a little power, nowhere near what is claimed. Very expensive too! Raise intake noise by around 1000% percent so say bye to any refinement your car may have before.
They don't actually fit the cars they are supposed to. Normally, they give you a load of hoses after removal of the airbox which you are told to let dangle around the engine bay as "They don't matter". Nice.
They are so well designed that they are shoved so that 40%of their surface area is in contact with the side of the battery. After a few months your car has 1/2 an air filter and an engine which runs on petrol, sulphuric acid and sponge!
Or the new one which gives you a pipe about 5 foot long coming off the turbo which you have to cut down or you can't shut the bonnet.
This is only a little bit, their T series turbo upgrades are the icing on the cake, but I will save them for another day.
Matt.