McLaren headlined the upgrade list published by the FIA ahead of track action beginning in Miami with 10 components listed.

That includes changes to the front wing, front suspension, front brake duct, sidepod inlet, engine cover and louvres, rear suspension, rear brake ducts, and beam wing.

Team boss Andrea Stella revealed Lando Norris has the full package fitted to his car, while Piastri has only some aspects of it.

“We have upgraded one car 100 percent and the other car sort of 50 percent,” Stella confessed.

“We obviously tested a combination of the upgrades and still there was enough communication between the parts of the car that it was possible to upgrade with 50 percent,” he added.

“It is the front wing on one car without necessarily having to modify the floor and the sidepods at the same time.”

The upgrade is aimed at addressing a perceived weakness in slow-speed corners.

“I think that achieving a good compromise between the low-speed and high-speed is difficult with every kind of car, and for different specific reasons,” Stella explained.

“Normally one of the reasons is always ride height because even the previous generation of cars were achieving a level of ground effect, but these cars are much more reliant on ground effect.

“So for this car, it is much more an element of the distance to the ground and how you manage what’s happening in the floor, around the floor and under the floor.

“It is a function of the distance to the ground.”

Stella did confirm Piastri will have the full suite of parts available at the next event in Imola.

“It is not really a shortage of parts, it is that the upgrades require quite a lot of work,” he revealed.

“We need to prove out that they work from a mechanical and aerodynamic point of view, that’s why you only go with one car.

“It is not only the back to back why you split,” he added of the fact Piastri and Norris have different spec cars this weekend.

“The changes in this kind of upgrade to sidepods and floor is very involved in terms of the design and in terms of building the car and so on, so you also do it to make sure everything runs reliably.

“It is not only the performance comparison, if that makes sense.”

After a slow start to the 2023 campaign, McLaren made huge strides mid-season courtesy of two specific upgrades.

While it first introduced parts for the Azerbaijan Grand Prix, that merely changed the development direction for the squad.

The full benefit of that was only revealed when a second package arrived for Norris at the Austrian Grand Prix.

Further updates in Singapore confirmed the team’s position at the front of the field, a dramatic turnaround, having been last in the championship after the opening two rounds.

Ahead of 2024, Stella had suggested the team’s design department had maintained that trajectory in the development of the MCL38.

That has proved to be the case thus far, with McLaren easily the third-best car behind Red Bull Racing and Ferrari in the opening five races of the year.

Heading into Miami, Piastri had suggested the new package this weekend is a reasonable step forward, based on what the team had seen in CFD and the simulator.

“We expect a slightly smaller upgrade than Austria last year,” he reasoned.

“If Austria was a second per lap then we would be leading the championship, but because we are not leading the championship then Austria was not a second per lap.

“I would say one second is the overall improvement we achieved last year across Austria and Singapore.”

Introducing the package in Miami is a risk, given the Sprint format employed.

McLaren had just an hour of free practice to assess its upgrade before Sprint Qualifying, at which point the car enters parc ferme.

Given the Miami International Autodrome is also a street circuit, the risk of damaging the new parts is also high.

“In terms of parts, yes,” he said when asked if the team had spares available.

“The main issue with it being a Sprint event is that after one hour that is it in the timetable [for practice].

“That’s why operations of this kind definitely don’t come without some risk, you just have to manage this kind of risk in the most thorough, proactive and forward-thinking way you can.

“That’s what we attempted, but we are ready to face some surprises – hopefully not too dramatic and we hope that we will be able to run [without issues] throughout.”

Opening practice was interrupted early when Charles Leclerc spun heading onto the back straight, prompting an eight-minute interruption.

Norris also battled an unrelated power steering issue through the opening hour.

However, Piastri was second fastest, 0.105s slower than pace-setter Max Verstappen.