Like a cross between an old-school Ferrari and an Ariel Atom, this ultra-lightweight, 400-horsepower overgrown Aussie go-kart is set up to destroy machines 5 to 10 times as expensive on the track.

Sydney-based brothers Peter and Nick Pap (short for Papanicolau) originally started the Spartan project as a way to build the machine they wanted to drive. Growing up riding and testing motorcycles, they found it hard to get much of a buzz on four wheels. "I've been a mad supercar lover since I was a kid," Peter told us over the phone. "Had the poster of the Countach, all that sort of thing. But honestly, I found there just wasn't enough real performance there. I preferred driving the go-karts, honestly, than any car."

So the idea of the Spartan was to bring motorcycle levels of acceleration and performance into the four-wheeled driving experience. The brothers started out by building a 400-odd kilogram car with a Ducati motor in it. "It had the Ducati gearing," says Pap, "and mate, I had that thing up to about 270 km/h on the straight at the Farm in NSW, which is a private track, kind of like a mini Nurburgring. It was a bit doughy down low, but boy was it quick."

From there, the brothers moved to a Honda Jazz engine, adding horsepower and drivability to their prototype. And after putting the whole thing through CAD design and sorting out a manufacturing chain, they're ready to start selling a new production Spartan track car internationally.

The production car will be based on the 2.4-liter engine out of a Honda Accord, which will be sourced second-hand, then torn down and rebuilt with new rings, pistons, bearings, rods and anything else it needs. A lightweight flywheel will make things a little more lively on the throttle, and a heavier duty clutch will be added. A Rotrex supercharger will contribute a mild boost, taking horsepower up to around 400.

This will go through a sequential Quaife gearbox – lever operated as standard, but with optional paddle shift. "The Transmission is bombproof," says Pap, "and the motor will take up to 700 horsepower. The whole engine is highly understressed, it'll run for years needing nothing but oil changes."

The car is incredibly lightweight. "We use a tubular space frame chassis," says Pap. "It's made out of 350 MPA, the stuff they make the roll cages for the V8 Supercars out of. Three times stronger than normal mild steel. Cold drawn, and instead of making just the roll cage out of it, we've used it for the whole chassis."

Likewise, the Spartan's entire bodywork comprises 20 kilos (44 lb) of carbon fiber, held on with quick-release fasteners. "We can't get the whole car under 550 kilos (1212 lb)," says Pap, "but you don't really need to. Once you get down to those weights, you've got more than enough power."

At 400 horsepower and 550 kg, it's got 80 horses over the Ariel Atom 4, and weighs nearly 50 kilos less. The Atom is an absolute face-rippling savage of a thing, hitting 100 km/h (62 mph) in less than three seconds from a standing start. The Spartan will knock off the same target in about 2.4 seconds. "Our prototype's doing it in 3 seconds, but with the production machine, 2.4 should be easily achievable," says Pap. "That's what we're quoting on the website, we actually think it might go quicker."

By the time we see the production machines, says Pap, they'll be wearing a little more in terms of aerodynamics, including a front splitter, side skirts and a small rear wing. "But we don't want to ruin the experience," says Pap. "The experience is the key. When you have too much aero, then when you lose it in a corner, things go straight off the track. We've got to be careful not to lose that feeling of being able to drift it and play with it, that's our whole focus."

The base price for a satin-finished carbon Spartan will be AU$150,000, or about US$104,000. That's about twice what you'd pay for a stock Atom, but Spartan is hoping the additional performance and full lightweight bodywork will set it apart.

"We'll probably get a slice of the market from guys who are looking for something a bit different," says Pap. "150 grand in Australian money sounds like a lot, but this thing will be running against McLarens and Ferraris and Lamborghinis, and their costs are enormous.

"Supercars will fry your tires in a day, at six or eight grand a set. Then you're looking at running costs: clutches, engines, this, that and the other, mechanicals. Our car, the tires will do six track days, and they cost 1600 bucks Australian a set. The brakes, well, we've never done a set of brake pads on our prototypes. They've just never worn out, because the car's so light. At Eastern Creek, the supercars are braking at the 150 marker, the little Elises are braking at the 50 marker, and I'm going under the Elises everywhere. The brakes are phenomenal.

"And it's other things too. I mean, you blow a clutch? It's 500 bucks plus the mechanic's time, which is peanuts, because any mechanic can do it. The whole engine's super accessible. So over a period of time, this thing is super cheap to run. We really only do oil changes on the prototypes, it's a Honda engine, it's pretty much bulletproof. And it's understressed by a long shot at 400 horsepower. You're not up into the big bikkies."

While the Spartan is currently only track legal, Pap says it wouldn't need a lot to make it street legal, and he's considering doing so. Headlights, indicators and inertial seat belts may be all it takes. And the team is working with suspension guru Dejan Ninic from Envirage, who has tuned the car's Ohlins TTX suspension in his downtime from running race teams and developing World Time Attack champion Porsches. Ninic has developed an adaptive suspension setup that may become an option on the Spartan car if it's made road legal. "Having adaptive dampers would allow us to have a couple of different modes," says Pap. "Wet mode, normal road mode, race mode… It also allows us to put a lift kit in it too, so you could drive it around to get to the track, then drop it down again. You can't drive the damn thing around on the street when it's 70 mm off the ground."

Pap tells us he's hoping a "credible car magazine" will put the prototype through its paces on track to verify everything he and his brother are saying about the Spartan. "You can almost drive it like you ride a motorcycle," he says. "You can get really hard on the brakes, I'm talking really late, and you can almost brake to the apex, you don't need to brake in a straight line, and then it's straight on the gas and out of the corner, laying big fat black marks and going "see ya later!" It's very agile, neutral, confidence-inspiring. If you lose grip, you don't just spear off the track, you can hang it out six or twelve inches very comfortably, and it's highly adjustable.

"But at the end of the day, we can say whatever we want. Somebody needs to come and drive it, and really experience what's good and bad about it."

Check out a video of an early prototype in action below.

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