McLaren-Honda's 2015 Formula 1 season has been a thorough disappointment by anyone's standards, and there is no reason to expect that to change in the Belgian Grand Prix.

Honda has spent three tokens and upgraded its V6 combustion engine for this weekend's Spa race, which raised hopes this might carry the revived Woking/Sakura alliance closer to the front of the F1 field.

That is not going to happen in Belgium. Jenson Button and Fernando Alonso set the 17th and 18th fastest times in Friday practice, which placed them 2.469 seconds and 3.185s respectively adrift of the pace set by Nico Rosberg's Mercedes.

That casts McLaren's multiple world champion driver line-up adrift in a no-man's land between Felipe Massa's Williams (in 16th) and Will Stevens' Manor/Marussia, which was 1.495s slower than Alonso.

So far so normal, you might think. But McLaren-Honda has recently been much more competitive than that - drawing ahead of Sauber into the thick of the midfield fight, and even successfully racing against Toro Rosso during last month's Hungarian GP, where Alonso finished a season's best fifth.

McLaren was celebrating a breakthrough in Hungary © LAT

Now, Spa is no Hungaroring. In fact they couldn't be more different. The Hungaroring is all short straights and twists and turns; Spa is mostly fast corners and long, brutal straights.

No wonder Honda wanted to introduce a mid-season engine upgrade, which the company's motorsport boss Yasuhisa Arai hoped would match Ferrari's power output.

It would be easy to glance at Friday's performance and conclude Honda has failed miserably in its mission, especially when Sauber drivers Marcus Ericsson and Felipe Nasr - both running with the latest specification of Ferrari engine for the first time - lapped fast enough to occupy places in the top 10 on the timesheet.

If Sauber, which has broadly been competing at the same level as McLaren-Honda for most of the season, can bolt in a new engine and jump into the top 10, why can't McLaren do the same?

The answer is 'inefficiency'. Honda's new internal combustion engine is actually an improvement over the old version, according to the team, but its Energy Recovery System is still not up to scratch, something that is not so costly on short, sharp circuits like the Hungaroring or Monaco, but is brutally exposed at places like Silverstone and Spa...

"We knew that Spa would not suit us," McLaren racing director Eric Boullier tells AUTOSPORT. "We are not at the level of power of the big teams. But it is not just power, it's more complex, it is [energy] deployment [as well].

"If you can use your MGU-K [properly], that's roughly 150bhp [extra]; if you can't it's 150 horsepower less. Today we don't have the most powerful ICE, we can't use our MGU-K like the others; we are suffering every race, but here it is worse than ever."

Spa's long straight exacerbate Honda's problems © XPB

The problem is that Honda's MGU-H is not sufficiently efficient to recover enough energy from the exhaust system to help the MGU-K in giving the power unit its extra boost of electrical energy for long enough to run competitively on a circuit at which the driver spends around 65 per cent of the lap at full throttle.

"The MGU-H for us is not capable like the others to recharge the battery and support the MGU-K," explains Boullier.

"We have the limitation of 4Megajoules per lap, so we burn our 4MJ, but when we burn them we still have not finished the lap, and then it [the ERS deployment] stops working.

"The ICE is better, and looks reliable so far, the biggest hurt is that we can't use all of our electrical power on the lap."

The bad news for McLaren fans is that Boullier says there is no chance of improvement in this area until the winter, because it will cost Honda "too many tokens" to make the changes now.

So it seems McLaren will be stuck with this problem for the rest of the season. That means its best hope of scoring strong results will come on tracks where this deficit can be minimised, such as Singapore.

Sorting the MGU-H was key to Ferrari becoming a winner again so quickly in 2015 © XPB

This year is therefore pretty much a write-off for McLaren-Honda as far as results are concerned, so the focus will be on building for 2016.

Ferrari has shown already how far it is possible to progress once you get the MGU-H working properly to "support the MGU-K", as Boullier puts it, so McLaren should be in much better shape once Honda gets on top of that conundrum.

"You see the big step for Ferrari [from 2014-15] was fixing the MGU-H," adds Boullier. "Honda is working very hard on next year and it looks like they have a plan to have a very good one next year."

In the meantime, the proud Woking outfit will have to endure a considerable amount more competitive (and thus financial) pain.

That's not to say Honda should take all of the blame for the current predicament. The McLaren MP4-30 has some weaknesses too, particularly in high-speed corners.

"To be fair with Honda, we have a chassis which is better than last year but we don't have the best chassis in the pitlane yet," Boullier confirms.

"So there are some glitches here and there to fix for us, and our car is quite draggy.

"In slow and medium corners our car is actually maybe the fastest one, but in fast corners we miss the power and we aren't as good as we would like."

But the team plans to introduce a new "Red Bull-style" front wing for September's Singapore GP. Red Bull has enjoyed a large upturn in form since introducing its own new element at Silverstone in July, and the hope at McLaren is that it can follow suit and possibly at least save some face in what must surely go down as the most trying F1 campaign in the team's long and proud history.

THE BATTLE AT THE FRONT

Reigning world champion Lewis Hamilton trailed his Mercedes team-mate Nico Rosberg by 0.302s at the opposite end of the timesheet to where McLaren currently finds itself.

Hamilton put most of this down to a straightline speed deficit, which may be the result of wing settings, rather than any variance in outright engine performance.

However the two Mercedes W06s were configured, they were streets ahead of the competition over a single lap on the softer tyre at Spa.

PURE PACE RANKING

1. Mercedes (Rosberg) 1m49.385s
2. Red Bull (Ricciardo) 1m50.136s
3. Ferrari (Raikkonen) 1m50.461s
4. Force India (Hulkenberg) 1m50.461s
5. Lotus (Grosjean) 1m50.489s
6. Sauber (Ericsson) 1m50.709s
7. Toro Rosso (Sainz) 1m51.037s
8. Williams (Bottas) 1m51.250s
9. McLaren (Button) 1m51.854s
10. Manor (Stevens) 1m54.065s

This suggests Hamilton might be suffering a bout of over-optimism in reckoning Mercedes is in for a close fight with Red Bull and Ferrari here.

Certainly Red Bull has improved recently, but to expect the Renault-powered RB11 to be as relatively competitive as it was in Hungary is a tall order on this type of track.

The relative strength of Force India and Lotus shows how important engine performance is here, and Williams will surely get significantly stronger on Saturday too, so Red Bull's best hope will likely be mixing it in the battle for the lower top-six places.

A crash for Ericsson was among the Friday interruptions © XPB

There is a suggestion that Toro Rosso took out too much wing attempting to mitigate for its own lack of straightline speed, thus compromising the STR10 in the section of track from Les Combes to Stavelot where it should be relatively strong.

Expect Carlos Sainz Jr and Max Verstappen to do better if STR strikes a better balance in this area.

A lot ultimately will depend on race pace of course, and a messy afternoon session, in which Rosberg's Mercedes shed its right-rear tyre before Ericsson crashed his Sauber heavily at Pouhon, featured two red flags and robbed the drivers of the chance to do any meaningful longer runs.

Rosberg felt he was "sort of one step ahead" of Hamilton in practice, but a comparison of the few heavier-fuelled laps they did both complete on the softer tyre suggests they are actually neck and neck at present.

Ferrari's Sebastian Vettel endured a difficult second session, ending up only 10th fastest overall, but his final two flying laps on heavy fuel pretty much matched the Mercedes drivers.

It's difficult to extrapolate from such a small sample of course, and the lack of consecutive laps means we have no idea of tyre degradation, but if Vettel can qualify in his usual third position, make another demon start, and repeat his late Friday practice pace, then perhaps Hamilton and Rosberg could find themselves under pressure again come Sunday afternoon.

Rather like McLaren-Honda, we can but hope...