i ran coppers on my 33 at 14psi and they lasted 10,000kms before i changed them, and they weren't missing at all. they still had probably another 5,000 or 10,000kms in them. they are less than $4 each, so it isn't that expensive. the iridiums i took out of my car were supposedly only about 20,000km old and they were shagged. iridiums are about $25 each and don't really last that much longer. if you use coppers, the money you will spend on spark plugs over a 50,000km period would be the same as buying 1 set of iridiums.