Circuit Driver Magazine - "The Pressure Principle"

It's already the quickest thing round most circuits but the guys at Radical have gone another step forward and turbocharged the SR3. Get ready, then, for the mother of all track day cars in this exclusive first drive.

Bruntingthorpe on what is so far the second hottest day of the year. Normally this place has its own weather system, a sort of 12 month winter, but today in a three layer race suit I reckon I'm possibly the hottest person on the planet. Emerging from the heat haze on the main straight and heading for us fast is a Radical SR3 albeit one with a major difference in the plumbing department. It streaks past flat in sixth at 160+mph. The noise is different. It's not that high pitched bike-engined yowl, it's gruff with a fluttering edginess. Down three gears for the tight end corner and a huge flame rips out of the exhaust pipe threatening to ignite the seemingly burning atmosphere. Accelerating hard now and there's no mistaking that familiar chirrup and sheer surge of noise. Yup, those boys at Radical have gone and strapped a turbocharger on to the SR3.

Actually to imply that this thing has been 'strapped' is something of an insult to the engineering capabilities of Mick Hyde and engineering guru Phil Abbott. Predictably and typically this is another neat piece of Radical creativity. Neat enough and powerful enough for the car to have just blown a hole through the Nürburgring lap record. With Phil Bennett at the wheel this very machine blitzed around the 12.8 mile circuit in a redefining 7min 19.7secs, which is an incredible 12.8secs quicker than the previous record held by a 600bhp Gemballa tweaked 911 Turbo. That is a huge chunk of time and a stunning drive from Bennett.

The full story has already been documented in Autocar so we'll leave it at that. Oh, except to say that Phil only had one flying lap and the car was/is far from fully developed and that there is undoubtedly more time to come. Some of that development work is happening right here, right now and Circuit Driver may not have been at the 'Ring but we will be the first mag' to actually drive the thing, hence being togged up in lovely heat absorbent Nomex.

Heat is the enemy
Of course the numbing flatness of Bruntingthorpe is light years away from the Nurburgring but today the heat and open expanses are ideal for testing a cooling system which proved a bit marginal during Bennett's Blitzen run. Heat is the enemy of the turbo particularly when applied to a smallish engine and one that doesn't have the biggest of water jackets to help cool it.

A turbo is, of course, one of the simplest means of generating big power. It's also rather crude and a crude application of the marvellous little spinning device results in all or nothing power delivery and bolshi off boost lethargy. As Phil Abbott puts it, "a turbo has to be managed to get the best out of it". Predictably, Radical took a look at the turbo conversions on the market for the Suzuki Hayabusa engine and… decided to develop their own. "It's easy to get 350bhp out of the Suzuki engine," says Phil, "but it's no good if that power kicks in in one great lump."

Phil and Radical tuning and engine building arm Powertec have produced an engine with progressive boost and a maximum output of 320bhyp which equals a power-to-weight ratio of over 600bhp per ton - a fairly mighty figure. The base for the engine is a 1500cc unit with a bottom end full of steel. It has an unusually high compression ratio for a turbo of 9.2:1 which helps the off boost characteristics. The turbo itself is a roller bearing Garrett unit that is tucked away behind the engine.

The real work is with the top end and the electronics. The standard induction system has been binned in favour of Radical's own specially cast plenum with just a single throttle body. A pair of exhaust cams controls the valves - a move that resulted in just the right amount of valve overlap. A bespoke engine management system from MBE effectively ties the whole package together enabling an ideal power curve to be plotted with just the right amount of ignition and fuelling to be dialled in against air rushing into the combustion chamber as the turbo does its thing.

Test driver for the day is super talented Dutchman Michael Verger currently to be found in the ASCAR series but equally well known as a single seater pedaller of repute and a long term Radical stalwart. He's also something of a hands on engineer too. With much of today's attention centred around the front end of the car, and getting the airflow to the radiator right, Vergers has been busy with the sheet metal fashioning scoops and deflectors. "I always like to engineer my own cars. Some drivers get too detached from the nuts and bolts of the cars. You've got to understand how it works to be able to drive it quickly," says Vergers.

Vergers has been in and out in five lap bursts monitoring temps. It's time to hitch a ride. We are effectively using half the circuit thanks to a new tarmac wiggle that has been put in which means we don't have to put up with the tedium of the two mile straight. Strapped in and ready to go. The flying Dutchman gives it maximum attack out of the pits and immediately my neck muscles start to work overtime as my crash helmet seemingly quadruples in weight under the fierce g-force induced acceleration. The tiny Radical shrinks the vastness of Bruntingthorpe's straights and sweeping bends in a way that few cars can. Up to the cut through and Vergers leaps on the brakes. The huge AP calipers and discs are almost F3 sized and at Nurburgring the telemetry measured 1.65g of braking force. It feels like that right now as again neck muscles work hard to keep my head upright.

Turbotastic
Out onto that heat hazed main straight accelerating hard in fourth. The turbo is force-feeding air into the combustion chambers, the injectors are wide open and the whole explosive mixture is being ignited by the tiny spark plugs. The power literally swells as the pressure builds and then releases as Vergers grabs the next gear. Fifth and then sixth and then we're out of gearing at just a smidge over 160mph.

On the brakes at the end of the main straight and again my head wobbles. The third gear corner is the tightest on the track and the sticky but road legal Dunlop Formula Rs fidget as the power is put down. The next straight is suitably demolished. Vergers keeps it nailed in fifth into the ultra fast but ever tightening left-hander. The invisible hand of downforce now comes into play and with foot planted the Radical boosts it way through at 130mph. End of the lap and three more to follow.

Back in the pits and time to monitor the mods. Temperatures are down but I'm still taking stock. It takes a very fast car to make this place feel small but the Radical has achieved it. The chassis, though, isn't overwhelmed by the power. It seems to handle it and in some respects the SR3 turbo now has the best of both worlds. It now has the power-to-weight ratio of the heavy hitting sports prototype (or at least British GT Championship fodder) yet retains the lightweight advantages that see it taking chunks out of the braking zones and that ability to carry huge speed through the corners. Which, I guess, is how it managed to lop 12.8secs off that lumbering Porsche around the 'Ring.

It doesn't appear to overwork its tyres either, which is crucial. That's a by-product of the progressive nature of the turbo.

Easy driver
There's the serious chance that the nose of the SR3 is going to have a hacksaw taken to it, so if I'm going to have a go it has to be now. No problem, I just hope I can do it some sort of justice. The cockpit is a familiar and immensely comfortable place, which is good. Of course the other great thing about the Radical is that actually driving it is a doddle. By that I mean the basic inputs of clutch gearchange, etc. Less to think about, you see.

Getting it off the line requires a bit more right foot than a normally aspirated SR3 but apart from that it's ultra docile. I trundle off short shifting through the gears, letting the boost build in sharp bursts, limiting myself to its potential. At this half pace the driveability and pick-up is exceptional, endorsing the amount of work that has gone into the turbo installation.

Ok, ok, I'll stop pansying around now. Through the wiggle keep it low in third and then on to the straight. Pedal and indeed metal make time-honoured contact but this time the sensation is enhanced thanks to a controlling influence on proceedings. The power when it comes is intense with a breathy hard-edged rush. There's no tailing off, it just keeps boosting until the shift lights go red and you pull back the sequential lever for another hit. My efforts of the fast left hander are somewhat more curious than Vergers' but I can feel the grip increasing and the tyres starting to get ever so slightly edgy. Oh, and those brakes. Powerful but with fantastic pedal feel they haul the Radical down with dizzying efficiency.

This is some weapon. The SR3 was already the fastest thing at most track days but this just blows it away. Indeed, with a SR3 in race spec present, the turbo car just breezes past it on the straight in the same way that an F1 car would waltz past an F3 machine. Performance figures? No standing starts as yet but expert 0-60mph in around 3secs and a 0-100mph time around 6secs or maybe even less given that the standard 1500cc SR3 will crack it in 8secs. A couple of rather sobering figures from the data logging at the Nurburgring though. How about: 70-150mph in 12secs? Or 50-100mph in just 4secs?

Slice of the action
Bruntingthorpe just doesn't do it any justice. Sure it's fast but you want the full experience. I'm thinking Donington Craner Curves, hard on the brakes for the Old Hairpin, a full on lap of the Brands Indy or GP Circuit or Castle Combe. Somewhere to gather the whole thing up and make it work. This place is just about the power and as ever that's only half the story.

Still, it's an impressive one. You can have a slice of the action too. Just 25 SR3 Turbos will be built and at £41,000 you might (or might not) have to save up. Still that's arguably not a lot for a car that can lap the Nürburgring in a smidgen over 7mins. Still, if turbos aren't your thing work will soon be commencing on the V8…