Toro Rosso's tech boss James Key is working hard to fit the team's new Honda engine into its 2018 chassis, a complex and time consuming exercise.
The decision to swap Renault power for the Japanese manufacturer's engine was decided last September, at a time when the design of Toro Rosso's 2018 charger was well under way.
Given the fundamentally different characteristics of the Honda unit, Key has been forced to re-design parts of the car's rear layout to comply with the new engine's specifications.
"It's a very compact unit, but a different architecture to the Renault, it requires a lot of adaptation work," Key told Speed Week.
With a big amount of aerodynamic work set in stone, Key found himself with a complex Chinese boxes effect on his hands.
"We try and stick to a rule that, if a car has already been in a development process for a while, not to upset any major items such as aero surfaces and that sort of thing, so we're not starting from scratch in too many areas," he told Motorsport.com.
"We've adapted the car under the skin as best we can. And that's led to quite a different approach to the chassis design, to the way the gearbox works, and so on.
"We've carried over the concepts and developed them further from this year's car."
Toro Rosso's 2018 car will also use a new gearbox designed in-house.
"Its layout and its size is different for this engine, compared to what we have this year. I think the concept is the same, but the architecture is different," he added.
"Some internals will carry over, some will be changed, some will be bespoke to the STR box. Otherwise it will be pretty close to what we've been running."