Because the teams have essentially said that. It can be few percent in terms of output performance, I believe. If you look back at Seb Vettel's last 4 races in 2009 they were all run on seriously used power units (he cracked open his 8th in Monza) - yet his speed was anything but compromised - winning both Suzuka and Abu Dhabi and looking very racey in both Singapore and Interlagos, and that was before Renault's reliability upgrades.
So its supposition.
While typical F1 engines are competitive the third time they are used, that does not mean that the manufacturer cannot produce a single race, higher performance engine, within the homologation rules. And likewise, why Renault may very well be providing MW with two, two race engines for the rest of the season. We simply do not know what the engine teams are doing. Such a two race engine spec would not surprise, because Renault's own cars have just gone to their 6th engines. When Renault did that change, they had three brand new engines, with 6 races left to go. The math is simple. Renault would use their single race 6th engines for the Singapore (the next GP). Hence after Singapore, both Renaults would have four races to go, and two brand new engines. If Webber runs his 6th engine for its third time at Singapore, he would be in exactly the same situation as the Renault team. IMO Renault would take advantage of having a two race engine spec. for the final four races.
Who knows what McLaren might do with Hamilton's engines? He would not have sustained any damage to his engine from Monza, and that 7th engine did not even do a race lap, just qualifying and morning practice. Its close to new also.
I do not believe that if the formula returned to single race engines within today's homologation rules, that such engines would have the same performance as a third race engine from this year. We already know too, that the engines do have limited maximum engine rev capabilities, which is the same thing as horsepower. Obviously if you can run full revs in a 70% full load road like Monza for 15% of the time, then if the engine was used just for Monza, then perhaps that could be extended to 45% of the time. Which would result in more horsepower for that engine, ignoring the other wear factors that would lower horsepower.
Last year was pretty strange for engine use, but the rules have changed a bit since then. Namely rule 28.4(a) has had an extra line added to it, which says:
If two such additional engines are used during a single Event the driver concerned will drop ten places on the starting grid at that Event and at the following Event.
This rule should not effect the main teams though, except for Ferrari.
For instance, Webber used his 6th engine for the first time in practice at Spa, but changed to his 7th engine for the race. Renault reported the engine was OK, but Webber never raced with it again. Webber is therefor better off for this season than last season with engine availability. I think that Singapore is the slowest race of the year, so its possible for Webber to used his 6th engine for its third use, and then just use his remain two engines twice each.
21 drivers put in new engines for Monza. Of those, most put in their 7th engine. Those that did not put in their seventh engines, were Kubica and Petrov (Renault) who put in their 6th engines; and Massa and Alonso, who put in their seventh engines. Those that did not change their engines, were Webber, Rubens and deLa Rossa. Webber (Renault) and Rubens (Cosworth) used their 6th engines for their second times, and Pedro used his 9th Ferrari engine for its second time. Liuzzi actually did not use his 7th engine in qualifying or the race, as it malfunctioned somehow, on both Saturday morning when it failed after a couple of laps, and it ran just on lap during Q1 (hard to believe isn't it?). Force India wrote a letter to the Stewards, we can presume about the Mercedes engine being faulty somehow, and he was allowed to us an old engine.
Edited by Melbourne Park, 16 September 2010 - 04:02.