Theon Design USA 002 4.0 | PH Review

Theon has a new Porsche 911 build, complete with its most powerful 4.0-litre yet

By Matt Bird / Sunday, 27 July 2025 / Loading comments

Yes, we know - yet another Porsche with the engine in the bum. There’s a break coming soon. It’s another old 911 that looks like an even older one but is packed with modern hardware, too - call it a restomod, reimagination, rework or whatever the correct terminology is this month. It’s from Theon Design as well, a company whose wares we’ve tested in the past. Revelatory, then, are likely to be thin on the ground.

On the other hand, this is a compact classic sports car that weighs just 1,150kg wet, develops than 420hp and employs a six-speed manual transmission. This whole contemporary classic space exists because it offers up so much of what is no longer available when buying new. Put it this way: we're talking Cayman GT4 power in Alpine A110 weight, so it ought to be pretty good. And right up our street.

Even beyond the usual appeal, this Theon commission boasts a few extra goodies. The 4.0-litre is now more powerful and torquier than ever, rated at 427hp at 7,400rpm and 330lb ft at 5,400rpm. It snorts through Jenvey throttle bodies, screams out of a switchable exhaust and sits in the back of a 964 like a fine bit of sculpture on a plinth. It really is some engine bay, with the air-con compressor and power steering pump now up front for an even cleaner look and trumpets standing proud. Additional points of note include an all-new carbon-ceramic braking system, with Brembo calipers, and the fact that this is the lightest build Theon has yet assembled. Every body panel bar the doors is carbon, and a new wiring loom saves 30kg on its own. Though pitched as the ultimate road spec, this is a two-seat 911.

A very, very pretty 911, too, obvious though it might sound. While a trend of late appears to have been to make caricature-spec 911s (looking at you, Gunther Werks, and some of the sillier Singers), there’s no mistaking this Theon build for anything but a very nicely presented old Porsche. Some may clock the wider tyres, larger calipers, and more aggressive stance, though likely not all. Everyone will be bowled over by the colour, for sure; Azzuro Thetys Metallic is familiar from the modern Porsche palette - see it on a GT3 RS here and a Turbo S here - while looking right at home on a backdated 964 as well. In the shade, it’s almost silver, the sun then helping it sparkle. The finish is flawless, of course. If the Theon doesn’t necessarily turn the dial any further for rebuilt old 911s in terms of appearance, that doesn’t make it any less lovely to look at.

It’s a similar story inside, crammed full of beautifully assembled old details, with modern influence if you know where to look. The dials are familiar and the pedals significantly offset by modern standards. The dash is pretty sparse and the toggle switches remain, only now they configure features like the sports exhaust and rear spoiler. Furthermore, while we’re used to perfectly put together old sports cars costing hundreds of thousands in 2025, it’s worth stressing again just how beautifully done a Theon car is. The client was keen for leather on just about every surface possible, so that’s exactly what they have, and it’s all exquisite. There’s an array of modern audio tech, too, including JL Audio amps and subs alongside Focal speakers; not that you’d ever tell, with everything integrated extremely discreetly.

It’s always a tad nerve-wracking driving old cars that have been built to a unique spec and feature a tonne of expensive bits to make them move. But despite now boasting more than 100hp per litre, this Theon is a cinch to drive slowly. There’s a pleasing heft to all the major controls, great signalling back to the driver about where the clutch bite is, what the brakes are doing and where the front wheels are, so it doesn’t feel like a total overload from the get-go. ‘True’ classics, for want of a better phrase, often seem to match one incredibly heavy control with another light and indistinct one; the steely cohesion of the Theon is welcome.

While this brief test drive was not the time to really push the new ceramic brakes, they further complement the feel of a rigorously honed, methodical build. The pedal feel is good, the performance clearly well beyond whatever a 1.1-tonne Porsche is going to need on the road, and probably the biggest benefit in everyday use is going to be for the ride with the reduction in unsprung mass. Despite the racy aesthetic and a tautness that feels pleasingly commensurate, the Theon is a long way from uncomfortable. The combination of the low mass, ceramic brakes and Tractive suspension make for a car you’d gladly drive to and from a track day, revelling in the agility and surefootedness on the way.

This 911 will probably be just as quick as conventional new cars when on circuit, too, thanks in large part to a mega flat-six. The 4.0-litre was always the star of the show for Theon builds, and never more so than now with the extra power and still a decent glug of torque. It means bimbling around at low speed is simpler than ever, without a hint of reluctance or recalcitrance. All the more reason to use something like it whenever there’s a chance. But given any opportunity to extend the flat six just a little, it’s absolutely wild, needle flinging itself from 4,500rpm to seven like the flipper of a pinball machine; no let up, no hesitation, just raw and relentless acceleration, gear after gear.

The Theon sounds like an old car, gruff and fierce throughout, while going like a new one; the claim is of a power-to-weight ratio to rival a 992 GT3 RS. Assuming the quoted kerbweights are comparable (i.e. similar amounts of fluids and fuel), then it does check out: 525hp and 1,450kg make for 362hp per tonne, 427hp and 1,150kg mean 371hp per tonne. So it’s always quite a lot faster than it ever needs to be, the 4.0 hollering through its rev range like a SoCal hot rod, and that feels fantastic. It wouldn’t be at all surprising to find existing customers with the 3.8 or slightly less potent 4.0 wanting an upgrade from Theon.

The gearbox is a treat, too, the six-speed 993 RS transmission a world away from old 911 gearboxes - if not quite as slick as the modern equivalent. Like the steering and the brakes, the shift requires some thought and some muscle, and is all the better for it. All of which combined makes for a very special little Porsche. Even on a drive that’s mostly pottering around country lanes, it feels more than adequately suited; rather than saving it for special occasions, you’re left thinking about any and every opportunity it could be used and enjoyed, such is the approachability and manifest quality.

We’ve been here before, of course. Many companies are building great 911-shaped cars at the moment, not least Theon itself. The cost— currently around 600,000 bucks, plus the donor car— is more than a mortgage for the average enthusiast. And there are lots of very nice modified Porsches out there to choose from that are not quite so extensively (read: expensively) overhauled. It’s a niche within a niche within a niche. All that being said, at a fairly glum time for UK automotive, this Theon is a shining example of what the expertise and talent in this country can achieve with a generous injection of time and money. It’s easily one of the best cars of this ilk we’ve tried, and given the abundance of such machinery that’s a pretty high bar. Ultimately, this a German sports car destined for the US that makes you prouder than ever to be British.

SPECIFICATION | PORSCHE 911 (964) BY THEON DESIGN

Engine: 4,000cc flat-six
Transmission: 6-speed manual, rear-wheel drive
Power (hp): 427@7,400rpm
Torque (lb ft): 330@5,400rpm
0-62mph: sub-4.0 seconds
Top speed: 185 (est.)
Weight: 1,150kg (wet)
MPG: N/A
CO2: N/A
Price: from c. $600,000, plus donor car, dependent on exchange rate