By Peter McLaren

Nicky Hayden still doesn't know which type of engine he'll be using at the 2008 MotoGP season opener, in Qatar on March 9, but suspects it could be last year's spring-valve design.

The two opening tests of the year - at Sepang and then Phillip Island - saw the lone Repsol Honda rider present, following Dani Pedrosa's hand injury, swapping between the new-for-2008 pneumatic-valve engine, which he hopes to race with, and the 'standard' spring-valve design from 2007.

The problem with the pneumatic-valve powerplant is that it is yet to match the performance of last year's engine - prompting Honda to fit the old spring-valve design into the new chassis, a combination that has been getting more and more track time.

Indeed, on his final pre-season visit to Sepang this week, Hayden rode only with the spring-valve engine, allowing him to concentrate on chassis and tyre development.

But the '07 engine/'08 chassis set-up is also far from ideal. The spring-valve, although better than the pneumatic engine, has still lost ground compared with the latest engines from Honda's leading rivals. Handling is also compromised, since the '08 RC212V chassis was designed specifically for use with the '08 (pneumatic-valve) engine.

"We didn't ride the pneumatic-valve engine at all this week. It's back in Japan and hopefully we'll see it again real soon, because that's what our potential is and obviously that's what this chassis is designed for," confirmed the 2006 MotoGP world champion, speaking exclusively to after concluding his Sepang schedule on Wednesday, a day earlier than his rivals.

Hayden, one of only nine riders at the final Sepang test, was second fastest to Fiat Yamaha's Valentino Rossi on both days, but unable to match his own qualifying or race tyre best from the January test (also set with the spring-valve engine). Overall, Hayden was 0.428secs behind Rossi on one-lap Michelin rubber, but the deficit on race tyres was a more worrying 0.98secs.

"The standard spring-valve engine isn't great. It's also not as good as the [spring-valve] engine we raced with here last year," revealed the American. "So that's a little bit frustrating."

"It's just a different engine," replied Nicky, when asked why it wasn't as good. "This engine spec is the spec Dani chose to go with for the spring-valve. It's smooth and easy to ride, but its overall performance isn't real high."

"We're down on radar speed, and acceleration mainly [even with the spring-valve engine]," he continued. "This week I didn't make a jump with qualifying tyres, as I would have liked, but I think generally I feel comfortable on qualifying tyres and they help our bike with acceleration, due to the extra corner speed."

Hayden believes it is unlikely that the spring-valve engine will be improved further, since all efforts are focused on bringing the pneumatic-valve engine up to speed.

"I'm not sure the spring-valve engine is going to get a lot of development from now on; it's hard to develop both engines," he said, when asked if the two designs could be developed simultaneously.

With just two more tests before the season-opening night race, Honda is facing a difficult decision in terms of which chassis/engine set-up to concentrate its immediate future on - and Pedrosa's injury has clouded the issue further, since the 2007 world championship runner-up needs to ride the latest version of both bikes to form a full opinion.

As such, a final decision only looks likely after Pedrosa's return to action, which the Spaniard hopes will take place next time out at Jerez, from February 16-18.

The official Jerez test might see the pneumatic-valve engine return to action, and the Spanish appearance is expected to be make-or-break in terms of whether the powerplant is raced at round one.

"Before I would have said 'yeah sure, we'll race the pneumatic-valve', but now maybe we're going to be on valve-springs [at Qatar]," admitted Hayden. "I don't want to commit one way or the other at this point."

But one thing that isn't in doubt is the effort Hayden and his team have put in to try and improve the situation.

"All I can do is ride the bike and focus on what I've got," reflected Nicky. "I think the bike will be all right. We'll see. We'll know a lot more when we get to that first race. We've made some progress, but for sure our rivals look real strong now, so we've got a lot of work still to do if we want to be a contender.

"My guys are working really hard. Everybody says 'it must be so hard for the riders, riding around Sepang in the heat all day' but honestly we've got the easy part!" he smiled. "The team has worked really hard here - and I appreciate that - even though we've still got work to do. We'll just keep trying to chip away."

Pneumatic-valves already control combustion-gas flow for the Suzuki GSV-R, Kawasaki ZX-RR and the latest Yamaha YZR-M1, while Ducati uses its trademark desmodromic valve system - making Honda the only factory team still running valve-springs.

The satellite Honda teams will get their first taste of the 2008 customer RC212V engine, with which Repsol Honda finished last season, at the official Jerez test.