Exclusive: Driving the first Caterham Seven powered by Horse

Horse has the capacity to make more than three million engines a year and wants automotive customers. Caterham has settled on its lightly turbocharged 1.3-litre four-cylinder, badged HR13DDT, made in Spain and already used in more than 20 models including the Renault Megane, Nissan Qashqai and Mercedes A-Class. So “it has been used in a number of cars and Horse has guaranteed supply well into the next decade”, says Laishley.

In existing production cars, the HR13DDT unit has standard outputs as little as 115bhp and as much as 160bhp, higher still where it’s already used in saloon car racing.

It has 1332cc capacity, a 72.2mm by 81.3mm bore/stroke, an aluminium block and head, direct injection, twin overhead cams, a lifetime timing chain and mirror bore coating, in which cylinders receive approximately 0.2mm of friction-reducing coating rather than a cast-iron cylinder liner (the sort that has a circa 2mm wall thickness). It’s tech the R35-generation Nissan GT-R received first and it gives “a lot of weight-saving in the block”, says Laishley.

The upshot, I’m told, is that the HR13 engine weighs 35kg less than a Duratec motor (around 15-25kg less than a Sigma, by my estimates), although some of that will be undone by the need for an intercooler and associated pipework and ducting. Complete, it certainly won’t weigh more than the Duratec, according to Laishley.

The final advantage is that “it fits”, says Laishley, although these things are somewhat relative. Most of it fits. A fuel pump and rail sprouts from the top of the engine, which the Caterham bonnet will have to be sculpted to clear.

It’s a tiny piece of the engine but one of the most critical. Various teams have contemplated rejigging it, but that it pressurises petrol to 350 bar has inclined them to leave it as designed.

I’ve come to Brands Hatch, where it’s binning down with rain, to try the first Caterham Horse prototype, an SV (wide-body) chassis in left-hand drive. The wider chassis gives Caterham’s team a bit more space to work with, and the exhaust and catalytic converter would foul the steering column on a right-hand-drive model, so they’re using this left-hooker while redesigning the exhaust.

A second prototype, an Academy race car, which has a narrow (Series 3) chassis in right-hand drive – and is thus representative of the first production versions – is in build at the factory.

I’ve seen some CAD mock-ups of the bonnet and the finished version will look much sleeker than the strictly functional add-on you see pictured here. It will want some additional cooling vents too.

Caterham’s engineers say that beyond ensuring the engine fits, they have done precious little to it. It makes 130bhp at around 5750rpm and builds in very linear fashion from 2000rpm, with a very flat torque plateau of a little under 130lb ft from 2000rpm to 5500rpm (bhp and lb ft being equal at 5252rpm).

The rev limit is 6500rpm but they say there’s no need to take it there, because torque and power both ebb away after the peak.

Caterham will use its own ECU (it’s more reliable than using an OEM ECU that requires “turning things off that don’t want to be”, says Laishley) and the base power might eventually go up or down a bit so that Academy race cars retain lap times as close as possible to those of today’s Sigma-engined cars.

In the meantime, there’s plenty else to be getting on with. Not only will there be a new engine, but also a new gearbox and limited-slip differential. Gearboxes are becoming the latest six- rather than five-speed Mazda MX-5 units and there will be a bespoke Caterham-specced LSD in place of the BMW one used now. The gearbox is a bit heavier than the five-speed but the LSD is lighter, so overall weight is the same.

Because of the new engine, gearbox and differential, the 2026 set of Academy cars won’t be available to home-build: the procedures simply won’t be finely honed enough, so Caterham will complete them all at the factory.

As I write, pricing has still to be confirmed, but I’m told it will be a little – but not prohibitively or mick-takingly – more expensive than a Sigma-engined car. The bits just cost more.

Those will be the first and, for the time being, only Horse-engined Caterhams. Historically, Academy cars typically become ‘Roadsport Championship’ race cars the year after they have competed in the Academy and then can be upgraded to 270 and 310 race cars thereafter: those championships, then, will have a mix of Horse and Sigma engines from 2028.

Entry-level 170s will still use the small Suzuki engine. Other road-going Caterhams will continue with Duratec engines until stocks run out. You can speculate that, with its various power options and obvious tuning capability, the Horse engine will become the norm thereafter: Caterham clearly hasn’t signed up a new engine maker to build just 34 cars a year. The other point to note is that if you want to have a naturally aspirated Seven, the time is now.

Caterham would like the new engine to feel as naturally aspirated as is possible, though. So at Brands I sink into the driver’s seat to receive a briefing, although there’s not much to tell.

There’s a light to warn of the impending rev limiter, but unless I deliberately take it there, I’ll have probably naturally felt the urge to shift up a gear by then. And while the sound is all authentic, there is a symposer (a tube and a vibrating membrane) to accentuate the induction noise.

By today’s standards, 100bhp per litre is modest and so is a redline in the mid-6000s. That redline and power output are figures an old 1.7-litre Ford Kent Crossflow would be familiar with. And if I told you that the Horse engine reminded me a bit of one of those, I wouldn’t mean it as an insult.

This is, I don’t think it’s unkind to say, a functional rather than spectacular sort of engine. It will pull at any revs because it has modern electronics but there’s notable response from 2000rpm and it pulls very keenly from 3000-5000rpm.

If there is turbo lag, and even at low boost pressures I suppose there must be some, you don’t really notice it in a car as light as a Seven. Perhaps it would be more notable in the dry, but in the wet there’s sufficient response to light up the rear tyres out of Druids hairpin easily, and even in higher-speed corners enough to straighten the car’s line without feeling like you’re waiting for the engine to do your bidding.

It’s just linear, progressive and responsive, and I think the symposer takes the edge off some gravelliness, to add some gruff induction ‘bwoap’.

It’s geared for around 3000rpm at 60mph in sixth, and while it’s hard to gauge how the large expanse of a race circuit totally matches the road, that and the ratios – with a gearshift every bit as tight and slick as the Mazda five-speed’s – feels ‘about right’.

In truth the whole package does. Would it be nicer if it was a super-light, naturally aspirated 1.6-litre that revved to 9000rpm and made 160bhp while it was getting there? Perhaps, but people don’t make engines like that which meet regulatory requirements any more.

The Horse engine hits the right numbers. And, in its delivery, in its responses, and even in its aural appeal, it largely hits the mark too. I think Academy drivers are going to have as much fun as ever. The future supply is pleasingly secure.