as far as we can tell nothing, it was recently compresion tested cos it dropped to five cylinders, and all cylinders where good (turned out to be a ecu fualt) then a little while later it just devolped a knock that has been put down to a big end, it has about 130,000 on it, but was blowing no smoke or anything and has always pulled pretty remarkable results with minor mods actually really disappointed to see it go but i got another motor to put in and need to sell this one to pay for it, the motor can still be started now and will run fine but we've avoided doing this naturally to avoid the chance of doing any damage