Mercedes technical director James Allison has revealed to an "intense effort" from the power unit department ahead of a significant rule tweak for this season.
Mercedes, along with fellow PU manufacturers Ferrari, Renault and Honda have all been allowed to deliver three upgrades to the system in recent seasons.
This has naturally provided that quartet with significant opportunity to make changes and deliver added performance when required at various times throughout the campaign.
But as part of ongoing cost-saving measures in Formula 1, for this season they are only being allowed the "one shot", as Allison describes it, to deliver an upgraded PU.
Across what is set to be a record-breaking 23-race campaign, it means there is pressure to ensure that sole upgrade delivers what is required, and at the right time.
"On the power unit side of the company, there has been a significant challenge," said Allison in a Mercedes video addressing the changes for this season.
"Quite aside from the fact that the power unit company has to find more performance from their PU, and the intense effort behind that, they had to do it in a context of a rule environment where there is less opportunity for mistakes.
"In 2020, and the years previously, there were three discrete opportunities in the year where an upgrade to the PU could arrive.
"With each new PU, you could have a different design and hopefully bring increasing performance with every power unit that you brought to the track."
Highlighting the difference for this year, Allison added: "In 2021, you are allowed just one opportunity to put that performance upgrade on the track.
"So, you need to know that you can pile as much goodness into that upgrade as possible and then make it stick because you just get that one shot at it."
"That really ramps up the pressure on the PU organisation to make sure that we get as much as possible from that single opportunity."
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