Jeep Grand Cherokee

A Jeep Grand Cherokee that won't go off-road sounds about as likely as one which is capable of outrunning a Porsche...

On the road, the SRT-8 is a vast improvement over the standard Grand Cherokee. Performance in a straight line is awesome, and the Jeep has sporty looks to match. There aren't any major dynamic flaws, although air-suspension would be a welcome option. But for £30,000 less than a Porsche with equivalent performance, the SRT-8 is superb value for money.

The sensational new Grand Cherokee SRT-8 not only has limited ability in the rough stuff, but is staking a claim to be the fastest 4x4 in the world.

At £40,000, the 6.1-litre V8 costs around half as much as the Porsche Cayenne Turbo. It might sound like an unusual creation for an American maker renowned for its models' all-terrain ability, rather than their outrageous speed, but on paper the SRT-8 is quicker from 0-60mph than the flagship Cayenne.

Auto Express was the first magazine to put these amazing claims to the test. Although the SRT-8's top speed is electronically limited to 155mph, parent firm Chrysler says a desresticted version of the V8-engined machine can eclipse the Porsche's 165mph maximum by 5mph.

The remarkable turn of speed comes as a result of boosting the capacity of the 5.7-litre HEMI engine up to 6.1 litres. This liberates 27 per cent more power from the unit, and increases its output from 330bhp to 420bhp.

But the engineers from Chrysler's Street and Racing Technology (SRT) tuning division responsible for the new Grand Cherokee haven't only concentrated on performance - they've also improved the driving experience. The traction control has been reprogrammed so it doesn't intervene as soon as before, or you can choose to switch it off.

Predictably, the car is very fast in a straight line, and sounds incredible, too. The monstrous machine is every bit as intimidating as you might imagine.

We also found the SRT-8 extremely entertaining through tight corners. This is because the 4x4 transmission has been redesigned, and a new lightweight transfer box channels 90 per cent of the power to the rear wheels.

To keep this under control in slippery conditions, sensors measure the lateral G-force, throttle angle and steering wheel inputs to moderate torque front to back, and send power to the front wheels if the rears start to spin.

Even so, the car needs to be treated with respect, and pressing the throttle too hard can cause it to head for the horizon with alarming speed. But once you've got over the mighty engine and its menacing growl, the vast improvement in driveability is clear. Particularly impressive is how much better the steering is over the standard car's. It's more precise and, thanks to a new suspension system, more responsive, too.

Nevertheless, the Grand Cherokee is a big vehicle, and when the four-piston Brembo brakes are applied the nose noticeably dives towards the tarmac.

To counter this, the car rides an inch lower - which bosses at SRT admit has robbed this Jeep of its off-road ability. Extra cooling ducts for the engine and brakes add to the sporty impression, and the car easily matches the Cayenne Turbo for brutish looks.

Probably its meanest angle is from the rear, where two four-inch exhausts poke through the valance. It's a view a lot of motorists will get of the SRT-8.

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