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Caterham

Caterham RST V8

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Two four-pot bike engines spliced together make a 340bhp V8 - and one wild seven

For many years, a V8 built from a pair of motorbike engines has been a tantalising dream. The potential of two powerful, in-line fours spliced to a common crankshaft is obvious and very appealing; low weight, high output and, importantly compared with four-cylinder 'bike engines so far installed in cars, much more torque. Yet despite the first prototype appearing the best part of ten years ago, nobody has been confident enough to put one into production.

Until now. This Caterham is fitted with a 2-litre V8 that weighs a mere 74kg yet develops a stonking 340bhp backed up by 190lb ft of torque. And it's very compact, too, measuring 19in long, 19in high and 19in wide. There are plenty of clues that this wide-bodied 'SV' Seven isn't standard, principally the bonnet scoop but also the many extra louvered vents let into the bonnet and sides. However, it's when the bonnet is lifted off that your pulse picks up. The tiny V8 is buried down between the chassis tubes, almost impossibly low - the tops of the eight carbonfibre throttle trumpets have a good couple of inches of headroom to the underside of the aluminium bonnet. Think what that does for the centre of gravity.

When it fires up, this compact V8 - dubbed the RST V8 - sounds urgent and inertia-less, like a four-cylinder bike engine but with an extra undercurrent of bass. It throttle-blips hungrily, the revs soaring and falling very rapidly, the blat of the twin exhaust pipes overridden by the staccato, machine-gun-like bark of the eight throttles gulping air.

This isn't a woofly V8. Like the V8 in the Ferrari 360, it has a flat-plane crank that synchronises firing pulses in opposing banks of cylinders so that it remains balanced at very high revs. While the 360 goes to 9000rpm, this pocket-sized V8 breaks through the 10K barrier. It would go to 15,000rpm(!) but in this application it's capped at 10,250rpm, partly because 340bhp is more than enough. The car's geared for 148mph in top and it has attained this speed on more than a few occasions during the engine validation process. Without a windscreen it would run to 160mph.

We're lucky enough to try the engine and the Seven before they're fully signed-off, so you'll have to excuse the temporary louvres, the extra sensors and wiring and the braided hoses that snake spaghetti-like around the engine bay.

The question is, why has it taken so long to get to get a 'bike-derived V8 into production? The man who knows better than anyone is Russell Savory, boss of Moto Power, which built this car, and also designer of the RST V8. 'Getting to the stage where you have an engine running on the dyno feels like 90 per cent there,' he says. 'In fact, you're only about 40 per cent of the way.'

The original prototype V8 that he built ten years ago was a pair of Yamaha EXUP 1000 motors spliced together. Individually they made about 130bhp but together they made 302bhp - even Savory was surprised. The reason, it transpired, was the dry sump lubrication system fitted to the V8. 'We hadn't realised how much power was sapped by the crankshaft churning the oil in the sump,' he says.

A flying start, then? Not exactly. There was interest in the engine back in the mid-Nineties, principally from Chris Craft who, with McLaren designer Gordon Murray, had created the Rocket, the first serious bike-engined road car. Craft's Light Car Company built the Rocket and a proposed second model, the Lightning, was designed with the new V8 in mind. That project didn't progress, though, and as Savory was being kept plenty busy enough running successful bike racing teams, the V8 was put on hold.

In the intervening years a whole host of bike-engined cars have appeared, driven partly by the increasing popularity of trackdays. Caterham, Westfield et al have developed and marketed bike-engined cars, and Radical's whole range is powered by developments of motors from two-wheelers. Interest in the V8 was picking up again, so Savory found an enthusiastic backer and 18 months ago rejuvenated the project.

From experience with that first V8, Savory knew there were still many design issues to be resolved before the new unit was a reliable, consistently potent engine. There are a number of other parties working on their own V8s so he's canny about certain details, but the RST V8 shares only its cylinder heads with the EXUP engine that spawned it. In time they will be replaced by bespoke items.

Essential to the performance of the RST V8 is the switch from the Yamaha's chain-driven cams, which originate in the centre of the engine, to a more conventional end-on belt-driven system. 'Even with a scavenge pump for each pair of cylinders, we found that after 20 minutes of running the chain drive would deposit all the oil at the top of the engine,' he says.

Why 'RST' V8? They are the first name initials of the prime movers behind the engine: Russell Savory, Tony Hart (brother of legendary engine builder Brian), and Simon Shaw, the backer. The 'T' also acknowledges Titan Motorsport, which has produced the castings for the development engines and will be supplying the production castings.

The bottom line is 340bhp at 10,250rpm and 190lb ft of torque between 7000 and 7800rpm, though it's worth noting that there is already over 100lb ft at 1300rpm, which is more than most four-cylinder bike engines produce at their peak.

Settling into the thin carbonfibre seat of the Seven, the main differences between this and any other SV are the bonnet scoop, carbon-knobbed sequential shift-lever, and the markings on the Stack digital display. Like the amplifiers in Spinal Tap, while the tacho normally goes to 10,000, this one goes to 13,000rpm.

The first 6000 are crammed into the first inch of the rev needle's sweep, which suggests there's not much action down there, but this isn't so.

The V8 fires up and settles to a busy
but very stable idle of around 1000rpm. Pull back on the lever and the sequential 'box clonks into first, squeeze the
throttle, bring in the clutch and it's a bit easier to get rolling than most bike-engined cars but there's still the feeling that the revs get knocked back more easily than in a conventional car.

Once rolling, the motor ambles up to 4000rpm with a smooth, bass-lite chug from the tailpipes on either side of the cockpit, but if you plant the throttle, the hard-edged, almost metallic smack of the intake side soon takes over. There's appreciable pull here but, as the rev- counter reaches 6000rpm, the rat-a-tat beat suddenly cleans up and hardens and the Seven takes off. By 7000 the V8 is into its stride, the note turns manic and the shove in the back becomes a slam. The rear tyres, road-biased Avon CR500s, are suddenly struggling to cope, and continue to do so right up to the rev-limiter. That's the story in the first four gears, the pace of the motor speeding the rear wheels to a fraction beyond that of the fronts but not to the degree that, in a straight line at least, you have to apply more than a few degrees of opposite lock.

The power curve isn't a curve at all but a straight line. This makes the Seven surprisingly easy to drive to the limiter, though for those of us more familiar with car-engine rev-ranges, it still feels unnatural to have so many revs left to go after 8000. It's quite satisfying to be able to edge the rear out of line with modest revs and then have lots left in reserve to be able to dictate the angle of the tail and ride out a monster slide.

Even in the wet the Seven demonstrates impressive straight-line traction; you just have to be on your toes if you use the torque to push the tail wide very early, such as on a wet roundabout. More of an issue here is the development sequential gearbox, which doesn't allow you to feather the downshifts or soften the pick-up of what is a fantastically snappy engine. For trackdays it would be the choice, but for the road an H-pattern - due to be installed very soon - would make a terrific difference to its driveability.

The pricing of this extraordinary engine is still being debated as we go to press. Presently it looks like being ΂£15K but if current business developments go the right way, it could be around ΂£10K. The gearbox is extra. At present, we're probably looking at a ΂£40K Seven. With more torque to come from a longer set of trumpets and a regular manual 'box, it'll be astonishing. If they can give its note a bit more character at the same time, it'll be even better, but maybe that's the V8 traditionalist in me coming out.

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evo RATING

 
[+]
Wild performance
[-]
Needs proper manual box

evo SPECIFICATIONS

 
Engine: V8, 2000cc, 40v
Max power: 340bhp @ 10,250rpm
Max torque: 190lb ft @ 7000-7800rpm
0 - 60mph: 3.4sec (est)
Top speed: 148mph (claimed)
Price: £40,000
On Sale: See text

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