Getting inside Honda's F1 power unit

Coming after a short break following the Japanese Grand Prix, teams haven't selected the Sochi circuit as a venue for technical updates, although the Russian GP weekend has presented itself as an opportunity to introduce new power units of new or existing specification.

With this weekend getting off to a slow start due to the cleaning of a diesel spillage before first practice, then rain for FP2, and FP3 being cut short following Carlos Sainz Jr's crash, the track will remain green and not rubber-in until much later in the weekend.

This means the tyres will struggle for grip, especially the fronts, inducing graining as they slide across the slick surface. Problems getting the tyres to work in these conditions will be exacerbated by the lack of running in representative track conditions.

In dry conditions traction problems can affect the rear tyres, with the super-softs being especially sensitive to their working temperature. In contrast to Singapore, it's likely they will run under temperature here in Russia.

The traction demands highlight Sochi as quite demanding for engine power, with fuel consumption being high, which will no doubt affect some drivers in managing power unit usage effectively during the race.

MCLAREN-HONDA

There are no major changes to the MP4-30 after the huge update in Singapore, but a representative power unit was on show at Honda's home race in Japan last time out, which revealed a few finer details.

From previous images of the real engine in the car, and the level of detail on the show engine, we can be sure this is based on a real power unit and learn some details from it. It's clear the entire package of the motor is compact, with all its ancillaries packed inside the outer envelope.

This allows for a better installation in the car, albeit with having to manage the temperatures of the various ancillaries due to their proximity to each other.

Since it was first seen, it has been confirmed the turbo compressor is mounted at the front of the engine, just inside the 'V' under the inlet plenum. However, initial speculation of the turbo being an axial type have been corrected by Honda.

Instead it is now understood the compressor is of a conventional type, but smaller, to fit into the space inside the engine's 'V', with the aluminium plenum above it lifted to clear the turbo's casing.

Alonso's McLaren had an updated petrol engine from Honda on Friday © LAT

The exhaust-driven turbine on the other end of the turbo is fed by the log-type exhausts, the casing featuring a double entry so each exhaust branch feeds in separately.

Additionally, each exhaust branch has its own wastegate to release excess exhaust pressure at full power.

This is used mainly to help with turbo lag, but not to prevent overboost, as the MGU-H is used to slow the turbo and recover energy in the process.

Honda spent its four remaining 2015 development tokens before heading to Russia and brought a new specification power unit to Sochi.

This was tested in Fernando Alonso's car in first free practice, before being replaced with an old specification unit, fitted with a new MGU-H and turbo parts.

The new-spec unit will be re-introduced at subsequent races.

It is understood Honda spent its tokens on a combustion upgrade and exhaust changes. Although engine suppliers must use their remaining tokens before the end of the year, there is not a requirement to run the updated parts at races, merely to have them made and run on a dyno.

In some respects it is a surprise that the petrol engine was upgraded within the power unit, as Honda firmly believes its internal combustion engine is more powerful than Renault's and close to Ferrari's, whereas it's the ERS that lacks performance.

The renewed quota of winter development tokens will therefore most likely be used on ERS updates for 2016, among which the turbo sizing will be a factor, as excess energy in the turbo can be recovered to add to the total energy output.

MERCEDES

Although the car's aerodynamic exterior is the area on show, it's actually the underside that creates the most aerodynamic performance. Naturally, teams guard these areas from view to preserve their technical secrets.

It first emerged in Japan that Mercedes has added a saw-tooth detail to the trailing edge of the front wing's two flaps. This saw-tooth edge has been added to the very front flap.

The slot formed between the two flap sections is generally a hard-worked area of the wing, feeding air smoothly from above the wing to underneath it. This helps keep the airflow attached to the wing's under surface for the most efficient aerodynamics.

If the airflow starts to separate under the wing, you have to open up the slot, which takes away some of the wing's downforce.

Adding this saw-tooth section breaks up what would otherwise be smooth airflow into tiny vortices forming at the tip of each tooth. This keeps the airflow attached without the loss in performance from a larger slot between the flaps.

TORO ROSSO

A small, unexpected change on the Toro Rosso was the addition of two small cooling inlets on the roll hoop on Carlos Sainz's car during free practice.

The STR10 already has a complex cooling set-up; the unusually large roll-hoop inlet feeding the engine's airbox, a large V-shape oil cooler mounted above the engine, and a small oil cooler above the gearbox.

This new inlet appears to be positioned to feed the gearbox-mounted cooler. This would free up the engine's airbox from its dual purpose of feeding the engine and the oil cooler.

It's not yet clear if this is simply a test of a 2016 concept, or if it will be on the car for the balance of the season.