With the recent introduction of its Factory Experimental (FX) class the NHRA has given a new lease of life to three engines from its Factory Stock Showdown (FSS) class. These are the Chevrolet COPO Camaro’s supercharged pushrod 16 valve LS V8, the Dodge Challenger Drag Pak’s supercharged pushrod 16 valve Gen III Hemi V8 and the Ford Mustang Cobra Jet’s supercharged twin overhead camshaft 32 valve Coyote V8.
Head to head FX racing was launched at the 2023 NHRA US Nationals at Indianapolis Raceway Park (August, 30-September 4), with just four cars in action, including one example of each marque. Full grids are anticipated by the end of next season.
The established top of the pyramid of professional level ‘doorslammer’ cars (ones having working doors) is Pro Stock. This clothes a tube frame chassis in a replica production car body whereas FX marries a tube frame chassis having replica and actual production panels to an engine from the production chassis-based FSS class.
Where Pro Stock uses naturally aspirated 500 cu in V8s, FX uses smaller displacement and less highly modified but equally powerful supercharged V8s. The FX car weighs a minimum of 2650 lb and has (nominal) 10.5 in-wide rear tyres, while Pro Stock benefits from 300 lb less weight and sports rear tyres just over 50% wider. Pro Stock cars run the quarter-mile in mid-6 second ETs, while the best FX time at IRP was posted by winner Greg Stanfield’s Chevrolet COPO Camaro at 7.236 seconds.
However, not only were there just four cars in action at IRP, there had been precious little prior shakedown running, so the potential of FX has yet to be established. The NHRA is anticipating these cars running 6.8 second ETs, maybe even one day snapping at the heels of Pro Stock. In the short term, FX is seen as a bridge between FSS and Pro Stock. In the longer term, as a less expensive option using engines closer to production, FX might conceivably come to supplant Pro Stock.
The performance of FSS engines is governed by the NHRA manipulating supercharger overdrive ratio. This and manipulation of car weight are intended to maintain parity between the contending marques. FX came into being with the same ratio designations as FSS but come the US Nationals and there was a change to the permitted ratio for a version of the Coyote that was not applied to FX. Moreover, FX specific ratio changes away from FSS were anticipated once the NHRA had evaluated the cars in competition.
Going forward, between FSS and FX there was also expected to be a different engine tune. Not only is the FX car 1000 lb lighter than the FSS and enjoying more grip (with 10.5 in rather than 9.0 in rear tyres) by regulation it also has a five speed manual rather than an automatic transmission, which means the engine can be kept within a narrower power band. Thus the engine builder will be looking at producing different output characteristics for FX compared to FSS.
Nevertheless at the opening US National event, Stanfield Racing Engines, which has been building the COPO Camaro LS for FSS for a good few years started with an unchanged power plant for FX. Winner Greg Stanfield noted that the initial focus was on “learning how to race these new cars”. He added: “When you see a performance gain, that's going to come from people getting the set-up on the car right. Getting the gear ratios right, the clutch right, the balance of the car right; all the package right.”
Specific engine development for FX thus awaits the new breed of car getting properly attuned to the NHRA’s quarter mile venues. Aside from Stanfield Racing Engines, FX engines were fielded at IRP by Tony Bischoff’s BES Racing Engines for Geoff Turk’s Dodge driven by Allen Johnson [the 2012 NHRA Pro Stock World Champion] and by Chris Holbrook’s Holbrook Racing Engines for his self-driven Ford.