Cosworth's involvement in American open-wheel racing stretches back to 1975, when the company developed the DFX — a destroked, turbocharged derivative of the legendary DFV Formula One engine — for CART IndyCar competition. The DFX displaced 2,650 cc, matching the turbo-class limit, and rapidly became the dominant unit in the series, ending the long reign of the Offenhauser and maintaining its position until the late 1980s. Ford subsequently backed Cosworth in developing the DFS, which blended DFR Formula One technology into the ageing DFX architecture, but that engine was eventually made obsolete as rivals advanced.
Cosworth then designed a new X-series of bespoke IndyCar engines, beginning with the XB in 1992. The series progressed through the XD before the XF was introduced for the 2000 season to replace it.
The XF engine retained the fundamental configuration of its predecessors: a 90-degree V8 with quadruple overhead camshafts, displacing 2,650 cc (the same swept volume as the original DFX). The most developed iteration was designated the XFE. In its 2004 specification, the XFE produced a rated output of approximately 750 horsepower at 1,054 mmHg of intake boost pressure, with a maximum figure of around 800 bhp during Push-to-Pass deployments at 1,130 mmHg boost. Maximum engine speed was held at 12,000 rpm by a mandatory rev limiter, a figure substantially lower than the over 15,000 rpm the engines had been capable of in the early 2000s before the series imposed restrictions. Peak torque was rated at 490 N·m. The engine was fuelled by methanol, used a steel crankshaft, and featured aluminium alloy pistons. The aluminium and iron turbo housing ran at a sea-level boost of approximately 5.9 psi. The complete unit weighed 120 kg and measured 539 mm in length.
Rated service life between rebuilds was 1,400 miles, after which teams were required to return engines to Cosworth for overhaul. This policy helped control overall operating costs for customer teams.
The XF was selected as the mandatory specification engine for the Champ Car World Series in 2003, making Cosworth the exclusive engine supplier to the series in that role. The adoption of a single-supplier spec formula was intended to reduce costs and level the competitive field, concentrating the championship's differentiation on chassis, aerodynamics, and driver skill rather than engine development budgets.
In 2007, Ford — which had provided financial backing and badging to Cosworth's racing programmes for many years — elected not to continue its sponsorship of the series. The Ford name was accordingly removed from the engine, and several other changes were made to the specification, most notably the removal of the calibrated pop-off valve that had been used to limit turbocharger boost pressure. Electronic engine management was substituted to perform the same limiting function. For that final Champ Car season, the series also switched to the new Panoz DP01 chassis, which was designed to provide improved airflow ducting into the engine.
Running parallel to the XF's life in Champ Car, Cosworth developed a related variant for the rival Indy Racing League. In mid-2003, Cosworth supplied a 3.5-litre V8 badged as the Chevrolet Gen 4 engine to IRL teams after the proprietary Chevrolet Gen 3 unit had proven inadequate against rival Honda and Toyota power. Known informally as the Chevworth, the engine was designated the XG internally. The XG finished second on its competitive debut at Michigan on 27 July 2003, and driver Sam Hornish Jr. went on to win three races that season using it. For 2004 the XG was reduced in displacement to 3.0 litres in line with revised IRL regulations, and it recorded one further victory in 2005 during what proved to be Chevrolet's final season in the IRL before the manufacturer withdrew from the series.
The Champ Car World Series merged with the Indy Racing League IndyCar Series ahead of the 2008 season. Cosworth did not continue as an engine supplier to the unified IndyCar Series following the merger, bringing the XF programme to a close. The convergence of the two competing American open-wheel series under the IndyCar banner was a landmark moment in the sport, and the XFE's role as the sole Champ Car engine through the series' final years made it a direct witness to that history.
The XF represented the culmination of Cosworth's continuous presence as an American open-wheel engine supplier that dated back to the DFX of 1975. Over more than three decades, Cosworth engines had powered victories at the Indianapolis 500 and across the CART championship, with the DFX alone achieving dominance through most of the 1980s. The X-series programme extended that lineage through the turbo era of Champ Car until the IRL's normally aspirated formula made a different technical approach necessary. When Chevrolet returned to IndyCar in 2012, it did so once again through a partnership with Ilmor rather than Cosworth, marking the end of the specific Cosworth-Chevrolet connection that had defined so much of the sport's engine landscape.