The subject of diffusers has come up time and again in Formula 1 since the last radical overhaul of the sport's technical regulations took effect at the start of 2009.
First there were the double diffusers, widely reported to be the main cause of Brawn's title success that year; then there were blown diffusers, and now it is specifically the act of off-throttle blowing of the items that is making headlines.
The FIA's decision to clamp down on this concept in time for the British Grand Prix has been met with a variety of different opinions through the paddock - from indifference by designers to frustration among the bean counters.
In explaining why such a move is needed, some background analysis is required.
McLaren is just one team using off-throttle blowing © sutton-images.com
When a driver opens the throttle of a Formula 1 car - or any road or racing car for that matter - the engine starts creating energy, the waste product of which is dissipated out through the exhaust pipes and - in the case of modern F1 - exited onto the diffuser's under surface to create extra downforce. This is known as blowing the diffuser and will be continued to be allowed in the sport for the foreseeable future.
For many years teams have been keeping the throttles 100 per cent open during braking. By reducing the fueling of the engine and retarding the ignition timing they have been able to achieve a situation where there is zero torque at the rear wheels.
This is a big bonus as it reduces the risk of locking the rears during downshifts while the engine RPM changes (due to the effects of the engine inertia). While this happens, the engine acts like a compressor, pumping air through and out of the exhaust system. When the exit is placed correctly this helps the efficiency of the diffuser. This has been accepted as a normal requirement and is called 'cold blowing'.
Now the engineers have come up with ways of putting more fuel into the system during braking. Because of the reduced ignition timing this fuel gets washed though into the exhaust system before it ignites, resulting in more energy in the exhaust waste gasses.
This improves the efficiency of the diffuser even more and is known as 'hot blowing'. It is this that has caused a rethink within the regulations.
Doing all this correctly has the effect of helping rear-end grip under braking, although in reality the gain is very minimal. Ross Brawn was quoted recently as saying that it gives you a second a lap, but I disagree. If you see a difference of more than 0.2s per lap, I think you're doing very well.
The idea of keeping the throttle open under braking has been around for a few years now, ever since BMW Sauber initiated the concept. To the team, it was not a performance-enhancing mechanism, merely a solution to a problem.
Off-throttle blowing has its recent orgins in the BMW Sauber squad © LAT
Robert Kubica often complained about the rear wheels of the car locking up under braking. The reason for this was that the characteristic of the BMW engine generated a lot of negative torque when the driver was off the throttle, and the solution was to keep the throttle open under braking and therefore enable the engine to rotate freely by allowing airflow through it.
This air was then blown out of the 'up and over' style exhaust system of a few years ago onto the rear bodywork rather than onto the diffuser.
The use of off-throttle blowing is being phased out in two steps. At Silverstone this weekend, a car will only be allowed to have its throttle open by roughly 10 per cent once the driver takes his foot off the accelerator pedal (the exact figure will vary from engine to engine). This is stage two. Prior to Valencia, throttles were allowed to be fully open when the accelerator pedal was not being pressed, while at Valencia (stage one), teams were told that any post-qualifying changes to the engine mapping would be banned. This was primarily to prevent teams from using a map that injected fuel into the engine during its 'off-throttle' phase in qualifying, but not during the race. So far this season, many teams have been using such a tactic because carrying the extra 10 per cent fuel required for one lap in qualifying is a far lesser weight penalty than carrying 10 per cent extra fuel for a 70-lap race.
What problem? I can't think of a coherent reason for such systems to be banned. It's not safety or reliability - we saw 24 cars, all with some form of exhaust blowing going on, make the finish at Valencia without bursting into flames! The only potential reason, in my opinion, is to prevent teams from having to spend money on ever more complex systems further down the line.
And why do it during the middle of a season? This is supposed to be cost-conscious F1, isn't it? And making any kind of rule change instantly costs teams money. Even sticking designers behind a desk to think about adapting to a rule change costs money. If they were going to change things, they (the FIA) should have made sure it happened at the end of the year instead.
Red Bull may actually gain from regulation changes © LAT
The system probably isn't that complex or that costly in F1 terms - not initially anyway. The problem is always that when one team is perceived to be getting a lot more out of a concept than the rest - Red Bull in this case - then the chasing pack all invest a lot of time and money in going down the route of working out what the top team's secret is. I don't think there is one, to be honest, but that won't stop them spending the money.
Further down the line the systems were bound to get very complex and very costly, so from that point of view, maybe it was inevitable that something would be done.
The winners and losers
There was a lot of hope among people inside and outside the paddock that Red Bull's pace advantage would be reduced by the regulation change, but this has not been the case on the evidence of Valencia. In fact, I'd expect Red Bull to actually gain from it. This is because Adrian Newey's car works spectacularly well as a whole aerodynamic concept, and is not just quick because of one item or another. For those teams that think Red Bull's advantage is just in its off-throttle diffuser blowing, they've got some waking up to do.
As I said earlier, I don't think you'll see more than a 0.2s difference in performance loss per lap compared to if the concept had not been banned. Where the effect should be more significant though is on the drivers. With rear ends now less stable under braking, drivers should be prone to making more mistakes, although that will probably depend on just how dependent their car's performance was on off-throttle blowing.