There's no reason to drive an automobile at 321km/h. No appointment is so important and no traffic cop that lenient. Few cars are even capable of that speed.

Imagine, though, that you're idling in a 1118kW car at the start of a 3km airport runway. And cleared for takeoff.

Wouldn't you want to break the 321km/h barrier?

I'm piloting a heavily customised Nissan GTR, dubbed the Alpha 12, with its ludicrous amount of power. I'm on a decommissioned Air Force runway in Michigan that once hosted B-52 bombers. It's wide and long enough for the task.

The Nissan GTR already qualifies as a supercar. The 2013 model costs US$100,000 (NZ$127,000) and delivers 406kW, hitting 100km/h in less than three seconds. That's enough power, right? Not for customers of AMS Performance, a West Chicago, Illinois-based tuning company. The 30-employee outfit has been around for more than a decade catering for a "mine is bigger than yours" demographic where more power is always better.

AMS specialises in "Alpha" performance packages for the GTR, rebuilding the V6 engine with sturdier parts, bigger turbochargers, special exhausts and reinforced transmissions.

Several engine components in AMS' GTR are sourced from New Zealand's Kelford Camtech and Dodsons, as both companies are experienced in building big-power Godzillas.

Light modifications start at US$6000. The Alpha 12 package costs US$100,000 on top of the US$100,000 of a new GT-R. For that you get a claimed 820kW with regular petrol and 1500 horses with 116-octane race fuel. The company says you can hit 100km/h in 2.4 seconds.

I want to see just how "real" the Alpha is, and I hope to top my personal speed record of 321km/h on a runway in a Lamborghini Gallardo four years ago. I'd rather not kill myself.
This is just a practice run, however, to get a feel for the Alpha's power.

AMS sales manager Eric Gaudi is riding shotgun. When I ask if he'd like to accompany me later on my top-speed run, he fires back, "Not a chance."

I roll on to the gas carefully, clicking through the gears well before the red line. The huge twin turbos quickly spool to capacity, sucking in massive gulps of air, and then expelling them harshly through the waste gates. It sounds like a jet engine.

We streak down the runway, faster and faster. I've got eyes only for the shift points on the tachometer and the tarmac in front of me. Gaudi is watching a special GPS device called a VBOX, more accurate than the speedometer, which tends to be inacurate at high speeds.

I slow down well before the halfway mark. Gaudi tells me I'm doing 320km/h - and I wasn't even trying.

The car is very controllable and not at all scary.

Gaudi's team adds race fuel to the tank and I take off - all alone now.

Accelerating toward and beyond 301km/h puts you in the death zone. If any little thing goes awry the situation can quickly turn critical. A strong cross-wind, a poorly timed sneeze or, my worst fear, a blown tire, and the car's straight-line trajectory could turn into an extended barrel roll.

The faster you go the more air the car has to displace. Past 290km/h it becomes a dense wall. The car becomes unstable, with air channelling underneath, trying to lift it skywards.

The AMS engineers estimate that the Alpha 12 is mechanically capable of hitting 383km/h. It has no special safety equipment. It's basically a street-legal car capable of more than four times the typical speed limit.

I stomp on the gas. There's a moment's pause as the turbos spool up to power. Then, like a match igniting gunpowder, a flash and a boom. The entire front of the car lifts.
I slam the gears into second, then third. There's a tingling at the nape of my neck. A sense of displacing air, space and reality.

The runway is crisscrossed by black skid marks left by jumbo-jet landings that seem to streak towards me as I land-speed over the wide runway. Then they, too, disappear. Number markers from one to 10 are on the side of the tarmac. At the halfway mark, not even looking at the speedometer, I let off the gas, step on the brake lightly and then much harder.

I'm almost disappointed when I stop and find the runway still continues on for quite a distance. The Alpha has a lot more to give.

I look at my top speed on the VBOX then turn around and cruise slowly back the way I've come. My heartbeat is fairly steady.

In 24 seconds I've travelled from zero to 344 kilometres an hour.

At a glance

Engine: 4.0-litre twin-turbo V6 with 820 kWs and 1220Nm of torque (1118kWs and 1423Nm with high-octane race gas), and 0-100km/h in 2.4 seconds.
Transmission: Six-speed dual-clutch automated transmission.
Price as tested: NZ$254,000.
Best feature: Insane top speed.
Worst feature: Few roads on Earth where you can use all that power.
Target buyer: The power-mad.