Audi is in the process of developing two new R8 variants to join the current V8 model, but according to one of the carmaker’s top execs the addition of these extra models will only make waiting lists longer. This will especially be the case in the United States where customers are already fighting for the 50 or so V8 models that make it across the Atlantic each month.

The new models include a high-performance ‘RS’ variant, which is expected to get the same 5.2L V10 engine from the S8, as well as a ‘Spyder’ convertible. The Spyder is scheduled to go on sale in the second half of next year, while the V10 RS won’t be unveiled until 2010 and could arrive in U.S. showrooms as late as 2011.

In the S8 the 5.2L V10 produces 450hp and a maximum torque of 398lbs-ft. Since this is only a slight improvement over the 414hp 4.2L V8 found in the current R8 we expect Audi will tweak the engine to make the V10 R8 a true supercar competitor.

Speaking with Car and Driver, Audi board member Michael Dick revealed that roughly 80% of customers are expected to opt for the more expensive and more powerful V10 model. The problem lies in the fact that Audi will only be able to produce 27 units per day for worldwide consumption, and of these less than half will be shipped to the U.S. The end result, he explained, will be longer waiting lists than the current V8 model, which for some customers can be more than eight months.

While the Spyder will help quell some of the demand, its volumes are expected to be lower than both the V10 and standard V8. Dick could not say how this third model would alter the overall mix but said its production will also be very low.

Hopes of a V12 diesel model, as previewed by the recent R8 TDI Concept, was also quashed by Dick, who confirmed there were no plans for production and even if there was it would be a Europe-only model.