A highlight of the Live Action Arena at this weekend’s Autosport International will be the ever-popular BriSCA Formula 1 stock cars. These V8 monsters are designed to race on short ovals and thrill with their fast-paced display and an aural assault that makes the grandstands shake.
But while BriSCA F1 machines are used to turning left, left, left and left again, Birmingham’s National Exhibition Centre isn’t quite their natural habitat. From March to November they compete on quarter-mile ovals, paved or with loose shale surfaces. Over a 70-year history, the formula has evolved from genuine ‘stock’ cars to highly specialised purpose-built machines with huge power combined with mean-looking steel bumpers and side rails to withstand the rigours of full-contact racing.
Perhaps the most visually striking feature of a BriSCA F1 stock car is its huge roof-mounted wing. These developed in two different directions: relatively conventional downforce-producing devices for sealed-surface tracks, and much taller, almost sail-like, sloping wings for racing on shale. Stability is key on the loose surface, where drivers also use the throttle to turn.
“When you pitch it into a corner, the stability of the wing holding the car is just immense,” explains three-time world champion Frankie Wainman Jr, whose self-built #515 car is a staple of the Live Action Area. “It’s very simple – you take the wing off, go into the corner at the same speed and it’ll spin straight round.”
Relatively low speeds make the benefits of genuine downforce marginal, even on asphalt. Wainman admits that it can be hard to notice, but a larger wing helped him win the Long Track World Championship’s final edition on Baarlo’s 1000-metre oval in the Netherlands in 1998. “Over there we’d be doing 120/130mph,” he says. “Boy, did it work.”
Stuart Smith Jr, who was forced to retire through injury shortly after winning his second world title in 2018, is a disciple of downforce on both surfaces. He continues to build cars that, unusually, feature similar wings for asphalt and shale. Smith’s wing, mounted high for a cleaner airflow to the aerodynamic main plane, rewards a neater style of driving deep into the bends before making a sharper turn.
“I wanted a wing that would keep my car straight entering the corner,” Smith explains. “And not necessarily one that holds you when you’re broadside. The car instantly had understeer into the corner, and we developed the set-up around that, and it worked. My shale car was arguably the quickest in the sport.”
For 2024, Smith is incorporating a conventional shale wing’s slope into his design, but with an aerodynamic profile. It’s been developed based on driver feedback and his own experience. “In stock car racing, you don’t have the time [to go testing],” he admits.
The wings give F1 stock cars their unique look, but arguably the biggest performance differentiator – especially on asphalt – is under the bonnet. Almost anything goes, so long as it’s normally aspirated and fed through a carburettor. In practice, that means big V8s. Massive big-block Chevrolets were once common but are now outnumbered by small-blocks, typically in 5.7-litre form, particularly on asphalt where engine-braking is more significant.
"As agricultural as stock cars may seem on the outside, to get them to their best performance and win the big races, you’ve got to know what you’re doing" Stuart Smith Jr
A limit of 7500rpm is a relatively recent restriction to keep costs in check.
“People were spinning them to 9000rpm and the engine-braking you get from that on Tarmac is immense,” explains Wainman. “An engine that revs to 7 and an engine that revs to 9, it’s like 30 grand’s worth of difference.”
Despite pump fuel effectively imposing a compression limit, headline power figures are north of 650bhp. “I do know lads now that are running 760-780bhp,” reckons Wainman. “If they were open compression, you’d be up to 850/900bhp.”
Development focuses on cylinder heads and valves. “It’s all NASCAR stuff and then we carry it on,” says Wainman, adding: “The tyres we’re running now are too good really.”
That better grip comes from American Racer rubber, although gravel rally tyres are also used on the inside wheels, which Wainman believes makes driveability less crucial: “When I was doing a lot of winning back in the day, you could have too much power. I had 500bhp and it was so easy to drive. They’re getting a bit lairy now, but the tyres are that bit softer and a bit wider, and it’s working for them.”
More power increases strain through the rest of the drivetrain. Most cars use the two-speed gearbox developed by celebrated drag racer Doug Nash. The rear axle was traditionally based on a Ford Transit’s, but the Ford 9-inch is now used to better handle the power. Suspension is largely free, except for (adjustable) spec GAZ shocks, leading to a variety of geometric solutions, but a simple Panhard rod is often favoured for its wide operating window and robustness.
“I’ve spent years messing about with Jacob’s ladders [as used on Sprint Cars] and Watts linkages,” says Wainman, “but you get reliability with Panhards.”
Locked differentials would cause understeer on corner entry were it not for the significant stagger that’s built into the chassis and adjusted via tyre sizes and pressures.
“Hitting the nail on the head is really technical,” Smith says of set-up, which also includes weight distribution (rules limit maximum rear and inside weight) and brake balance across all four corners.
“Tarmac, I’ve always said it’s 50% set-up and car, and 50% driver. On shale, it’s probably 75% driver and 25% car. You can get away with a lot of things on shale – it’s really forgiving.
“But in big races, you tend to be looking at being the fastest in the dry [towards the end of the race]. If you can have a car that’ll survive in the wet and be within touching distance of the fast lads, the time you’ll make up by being quick in the dry is significantly more.
“As agricultural as stock cars may seem on the outside, to get them to their best performance and win the big races, you’ve got to know what you’re doing.”
He adds with a chuckle: “But you know the beauty of stock car racing, I think, is they’ve all got front bumpers, so you can always stuff them [the opposition] in the fence. You’ve just got to hope that you haven’t got a target on your back!”
A BTCC racer’s verdict
“It’s probably one of the best things I’ve ever done in a race car,” enthuses Bobby Thompson, a British Touring Car Championship podium finisher. Thompson drove world champion Tom Harris’s machine from last to fifth in BriSCA Formula 1’s BTCC Challenge Trophy for tin-top stars at Skegness Raceway last November, and won the 2022 edition.
“Looking at the car, you think it’s going to be a bit of a boat, because of how big and heavy they are. But they’re actually a little bit more nimble than you first think.
“I think I had nearly 800bhp, so to lay that down is quite hard work. I think I got to full power once – you don’t really need to. But when you get into a rhythm with it, you can really get an idea of how nimble they actually are when they’re well set up.
“They’re quite responsive to every input. You can brake a lot later than you think – they stop rather well. And you can come off the brakes a lot, lot sooner than you think because the thing naturally wants to turn left.
“The only thing that you never get used to is the contact – it goes right up your spine. Even in touring cars, the cars are fairly stiff, but there’s still that crumple zone, whereas in a stock car it’s just metal on metal, and the only bit that moves is you in the middle.
“It’s the scariest thing I’ve ever done in a race car. If you tap someone out the way, you know you’re getting it back twice as hard into the next corner, so you’ve got to do the bloke in front fairly good so he doesn’t come back at you! But it is really fun. It’s definitely something I would be keen on doing again.”
