1275 unleaded cylinder head assembly, rebuilt, with valves and springs

There is no specific large-bore (1275cc-based) head casting number that will fit the 998 engine any easier than any other. They all have the same problems - generally requiring exhaust valve relief cut-outs machined into the block and re-alignment of the front water gallery transfer ports. However, I would avoid using heads with valves bigger than 35.7mm on the intake since these are too big for most 998 engines unless they are absolutely full-race spec where top end power at high rpm is all that is required.

The specter of 'unleaded fuel only' - instigated in UK on January 1st 1999 and seemingly from decades ago across the rest of the world - seems to be forcing more and more folk into frightened, panic orientated action.

The fuel situation seems to be worsening at a great pace these days. And as is exhibited by the questions that appear on the message board many folk are confused by what they can and can’t do, and what is best to do as far as race engines go. Many have posted (particularly from the States) that nothing need be done - just run on unleaded.

Everybody has their own opinion on this subject. The most experienced people will tell you that the best way to maintain your engine performance is to accept the fact that valve jobs need to be done 2 or 3 times more often than rings and bearings! And this data base was concluded when leaded gas was the norm! Now that unleaded is all you can get, valve jobs are needed even more often! The purpose of a valve job is two fold; first the valve seats. The impurities in the air and gas often get trapped between the valve and the seat in the head; under worst conditions stopping the valve from closing, but more commonly being smashed enough to allow just a little seepage of hot gases.