FIA regulations introduced for the 2005 WRC season mean that rallies are now 'paired' and WRC manufacturers must use one engine for two events. We spoke to SWRT Principal David Lapworth to find out what this means for the Subaru team and the Subaru Impreza WRC2005

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While the new rules don't make a major difference to the way that we design the engine, they do make a difference to the tactics of using an engine. Subaru has an excellent record of reliability and obviously that's something we think about as part of our engine development programme. The engine is an area of the car that can be pushed to the limit to obtain more power, but only at the expense of risk - we must balance performance against reliability. In the past, we tried not to be too greedy with power, but tactically increased the risk on some stages if we were fighting for a win. Now we have to complete two events with one engine, we're far less likely to do that on the first of the 'paired' events. Despite this, Subaru is still following a policy of going for wins rather than for points.

We have to build some safety margin into the engine if we're going to run the same specification all year. A low altitude, high-speed event such as Sweden places far greater stress on an engine than a high altitude event such as Mexico. FIA homologation regulations don't allow changes to the basic specification for each event.

The 'Mexico / New Zealand pairing' is probably the most interesting test of the new engine regulations. Mexico runs at more than 2000 metres above sea level and is very high altitude, while New Zealand is only a few hundred metres above sea level at most. In the past a different mechanical specification and a different compression ratio of engine may have been used for high events such as Mexico and Argentina, but from now on team's have to determine the best compromise."