Mercedes power made history at the iconic Indianapolis Motor Speedway back in 1994
There aren't many technical loopholes in motorsport history that have caused as much of a stir as when Mercedes-Benz tackled the Indianapolis 500, with a brand-new, purpose-built pushrod engine for the 1994 event.
Mercedes doesn't have the most obvious connection to the iconic oval race, but that link from 1994 is an incredibly special one - and this year marks the 25th anniversary of that very Indy 500 victory, Mercedes' second triumph at the event.
This remarkable story cemented itself in motorsport's history books on race day, Sunday 29 May, but the foundations for it began many, many months beforehand - in secret, at engine manufacturer Ilmor.
At the time, the CART series featured slightly different rules for the Indy 500 compared to the other races on the calendar, opening up the opportunity to create an engine specifically for the Indy 500. Penske grasped this chance with both hands.
Behind closed doors, Ilmor was tasked with creating a new Indy 500 engine for Penske in just 10 months, with work beginning in the summer of 1993. The product would eventually be called the Mercedes-Benz 500I, ominously nicknamed 'The Beast'.
It was a 3.4 litre, eight-cylinder turbo V8 pushrod engine, generating over 1,000 hp in total - around 200 hp more than the conventional V8s it was competing against. If you used a single-camshaft pushrod engine, you were permitted to design a higher capacity engine and run it at a higher boost level thus generating more power.
Reflecting on the project, Ilmor Engineering co-founder Mario Illien said: "It was definitely a challenge. Because, the timeframe for such an undertaking was almost impossible, every element had to be right or the project would fail.
"The effort and commitment required from everybody involved were immense. Everything had to be secret. The whole workforce involved at Ilmor and at Team Penske had strict instructions not to talk about it to anybody. That was an absolute key element."
Testing and development were conducted by Penske in Spring 1994, again in secret, before the PC-23 and its new Mercedes-Benz 500I engine broke cover for the first time in April - just a few days before running for the Indy 500 began.
"It was a tight schedule with a 'fixed end date' May 1994, no chance to carry it over to May 1995 as we all knew the governing body would change the rules and make it uncompetitive as soon as it became public," explained Graham Gant, who worked on machining the heads and cylinder blocks for the project and still works at Mercedes-AMG High Performance Powertrains today.
"Time was very precious, and every hour counted so finding solutions to issues quickly became a highly tuned process. The engine itself was a beautiful thing, a piece of engineering excellence."
It sent a shockwave through the Indy 500 paddock. No one outside of Ilmor, Mercedes and Penske knew of the project. And it's fair to say that impact continued through the Month of May.
Despite initial reliability issues in testing and practice, the Penske cars locked out pole position and P3 on the grid, with Al Unser Jr. at the head of the pack and Emerson Fittipaldi joining him on the front row. The third car of Paul Tracy lined up P25 after an accident in practice.
The extra punch of the Mercedes-powered Penske cars was most evident at the start, where Unser Jr. and Fittipaldi got the jump on the rest of the pack, storming into a commanding lead early in the race.
Unser Jr. lost P1 in the first round of pit stops after stalling his car, giving Fittipaldi the lead of the race - where he stretched out his lead with every lap, to almost 25 seconds by lap 85.
It wasn't to be for Fittipaldi in 1994, though. Despite his commanding performance, leading 145 laps, his race ended with 15 tours of the famous oval left to go. Running behind Unser Jr, who had just unlapped himself, Emerson lost the rear end at the exit of Turn 4 and tagged the barrier with his right-rear.
A crushing end to what had been a hugely controlled drive for Fittipaldi and leaving just one Penske car on track, after Tracy retired with engine trouble at the halfway mark. It wasn't over for Penske, though, as Unser Jr. was back in the lead - having been a lap down, a few moments earlier!
The late curveball with Fittipaldi's dramatic retirement promoted him to the P1 spot and he was able to bring the car home to win the Indy 500 for the second time in his career and give the Mercedes-Benz 500I victory on its debut.
It was also the second time Mercedes had powered a car to victory in the Indy 500, the first coming way back in 1915 when Ralph DePalma drove a Mercedes Grand Prix machine to triumph in just the fifth running of the event.
"Winning the Indy 500 - that means something," explained Norbert Haug, former boss of Mercedes-Benz Motorsport. "It was worldwide promotion for Mercedes-Benz, so it was easy to say yes when Ilmor suggested it to us."
A mixed bag in terms of results for the PC-23 at first glance, but in reality, this was one of the Indy 500's most commanding victories, a hugely memorable one in its history and also a remarkable engineering project for Mercedes and Ilmor - which those who worked on it still remember fondly today.
"I've become quite emotional writing this, so many memories" Graham said, while reflecting on the project 25 years on.
"It was absolutely top secret, no one knew about it" explained Paul Wisner, who worked in Inspection at Ilmor and still works in the same department, now at Mercedes-AMG High Performance Powertrains. "It was a nice pressure, you felt honoured to be in the programme. I still do even 25 years on."
"Winning the race was a fantastic feeling. That was the icing on the cake, for that particular project. Just for the audacity of it, it was an exciting time."
Sadly, the Mercedes-Benz 500I never raced again. A few weeks after the race, USAC changed the rules for purpose-built pushrod engines. The Beast had done its job, but was silenced from that moment onwards...