The hot hatchback genre was born in 1976 with the debut of the original Golf GTI, which boasted 110hp from its fuel-injected 1.6 litre motor, and the hot hatch war really got going in earnest when the 105hp 1.6 litre Ford Escort XR3i joining the fray in 1982.
Fast forward nearly four decades to 2013 and the 300hp VW Golf R 4Motion and 340hp five-cylinder Audi RS3 quattro were the fastest hot hatches on the planet until Mercedes-AMG dropped a bombshell with the 360hp A45 AMG.
Not only did the A45 AMG have more power it also had a superior chassis, and soon spawned saloon, estate and crossover variants to complete Mercedes dominance with a more comprehensive model offer.
In the process the compact high performance range also helped the Mercedes sporting sub-brand massively increase its worldwide sales, more than doubling market share in North America, Scandinavia, Austria and Switzerland where 4WD is a distinct advantage in winter.
Launched last year, the mainstream variants of the second generation A-Class hatch (W177) and CLA-Class (W178) saloon have been flying out of the showrooms, their AMG variants eagerly anticipated.
The outgoing M133 engine debuted with 360hp in 2013, and was ramped up to 381hp at facelift time. On paper the turbocharged four-cylinder motor at the heart of these latest cars appears very similar with exactly the same 1,991cc displacement, from an under-square 83.0 x 92.0 bore x stroke. But when you place them side-by-side they are very different.
“The primary reason for moving the turbocharger to the rear was to aid the lower bonnet line that gives this second-generation model line its sleeker looks and superior aerodynamics,” explained Natascha Bausewein, Lead Engineer for the M139 engine project. “Another positive point is that the exhaust no longer has to be routed under the engine to draw spent gases rearwards,” she said.
With a larger Borg Warner twin-scroll roller bearing turbocharger, which is basically one of the units from the AMG GT4, which features a 57mm diameter turbine wheel, the M139 motor weighs 160kg, which is around 10kg more thanks to the larger turbocharger and new items like the gasoline particulate filter.
As before the engine block is a closed deck design for strength. The pistons use the same low friction Nanoslide F1-derived coating and the combustion chambers have a similar part bowl-in piston design.
The exhaust camshaft features Camtronic variable valve timing. As before the Direct Injection operates at 200-bar pressure with Piezo nozzles that can fire up to five accurate pulses per combustion stroke. Conventional magnetically activated injectors add extra fuel during full throttle operation, and the peak cylinder combustion pressure is up by 10 bar to 160 bar.
Heat management is critical in modern engines because of increasingly stricter emissions standards. Fast warm up with near instant catalytic converter light off is required, and this is aided by a cooling system utilising a crank driven mechanical water pump for the cylinder head and an electrically driven one for the crankcase. This system allows the head to stay cool for efficient combustion, while a warmer crankcase makes for lower internal fiction.
With a compression ratio upped from 8.6:1 to 9.0:1 and a 2.1 bar boost pressure the base version of the all-new M139 motor produces 387hp at 6,500rpm with 480Nm of torque from 4,750-5,000rpm on 1.9 bar of boost.
The S version makes a sensational 421hp at 6,750rpm with 500Nm of torque from 5,000-5,250rpm with 2.1 bar boost (M139 1.8 bar for base and S variants), achieved with a different ECU map as well as a larger, two-stage intercooler that works in conjunction with the low temperature circuit of the air-conditioning.
Think about that 421hp number for a moment, because this is almost four times the output of the first generation Golf GTI and Escort XR3i! Another significant number is the specific output of 211hp/litre, which exceeds that of most current supercars.
And finally, where the old motor ran into its limiter at 6,700rpm the M139 now soars to a higher 7,200rpm electronic cap. This higher rev limit really helps on track or when you are charging a tight, twisty road in the lower ratios of the eight-speed AMG Speedshift 8G double-clutch paddle-shift transmission.
Thanks to the unerring grip of their 4Matic+ all-wheel-drive system all that output can be turned into a scorching 3.9 sec 0-100km/ time in the case of the A45 S, and 4.0 sec for the slightly heavier CLA45 S. The base models are 0.1 sec slower respectively. Top speed for all models is electronically limited to 250km/h, or 270km/h for S models with the AMG Driver’s Package.
Today, we are at the Jarama Circuit near Madrid, Spain ready to put the second generation A45 AMG and CLA45 AMG models through their paces on both road and track.
Both models feature the AMG Dynamic Select driving mode controller that offers a ‘Basic’ map that looks after ‘Slippery’ and ‘Comfort’ programmes. ‘Advanced’ looks after the ‘Sport’ mode while ‘Pro’ is mapped for the Sport+ mode.
Finally, ‘Master’ is linked to the ‘Race’ mode that is standard on the ‘S’ version and part of the optional AMG Dynamic Plus package on the base models. All these are accessed through the Dynamic Select button on the console and via the AMG menu on the MBUX infotainment screen.
One small point that might go relatively un-noticed but makes a marginal difference to the way the A45 and CLA45 grip and handle in extremis is a function of their styling.
“While the standard tyre size of both models is 245/40ZR18, with the 19-inch wheel and tyre option the CLA’s slightly wider wheel arches allowed us to squeeze in 255/35ZR19 tyre, which have a slightly larger tread contact patch than the 245/35ZR19s on the A45,” explained Driving Dynamics engineer, Rene Szczepek.
On public roads you don’t notice the slight difference in turn-in or grip levels, but on the race track the CLA 45 I drove first seemed to have a fraction more bite at the front end when turning in and a smidgen more poise in a four-wheel-drift on the limit, even if it was near impossible to split absolute mechanical grip by the seat of one’s pants.
That said I have to qualify this comment by laying out a couple of other observations. Firstly, all the cars were on standard street rubber and not trackday Cup tyres. Therefore in the 30+ degree C heat they began to wilt after a few laps, resulting in gradually increasing understeer and handling looseness. Secondly, because the track only cars had done many laps in the hands of drivers with varying styles and differing abilities, tyre wear across the fleet was not even.
With this in mind the CLA 45 I drove first seemed well bolted down and handled well, with a nice light to medium weighted feel through the typical thick rimmed, flat bottom AMG steering wheel.
As I encountered significant understeer with the first A45 at Jarama just as I had on the original A45 launch at Bilster Berg in 2013 I knew to ask for another car. As expected this was noticeably better, handling more like the CLA45 with crisper turn-in and a more neutral balance.
This tyre wear pattern is a factor that means impressions gleaned on the day are not 100% definitive, and the only way to reliably compare apples with apples is to use two cars with fresh rubber and optimum tyre pressures.
All else being equal the key to getting a clean turn-in to a bend is not being over ambitious with entry speeds. Get that right and in Sport, Sport+ and Track modes the new AMG Torque Control differential keenly shunts more power to the rear wheels, rebalancing the fundamental layout of front wheel drive with hung on all-wheel-drive.
Throttling up smoothly past the apex you get a pleasant feeling of power on slip at the rear wheels that you can play with to modify your exit line or just have a ball of fun with a smidgen of power on oversteer. And as with the E63 AMG and GT4 Coupe there is also a Drift mode where you can play hoonigan and light up the rubber when the mood takes you.
Like all hung-on 4WD systems these AMG models run in predominantly FWD mode until the sensors detect the needs to send some torque aft. AMG swear that the transition is seamless, but there were a couple of instances where I could feel the front wheels scrabbling for a fraction of a second before the clutches closed and shunted the power to the rear wheels.
Last year I detected the same phenomenon while testing the new Audi A6 40 TDI quattro, which has Audi’s ultra technology on demand 4WD system, so I don’t totally believe the hype surrounding such systems. In both cases I found the system can be felt engaging if you invoke sudden weight transfer with a big throttle opening combined with an uphill gradient or a loose surface like sand.
On the road both the A45 and CLA45 were an absolute delight, and it is very clear that the new generation cars have a much-improved ride/handling balance.
I used to grit my teeth at the harsh ride of the A45 AMG, much preferring the longer travel suspension and taller tyres on the GLA45 AMG, which despite its elevated ride height is a mere 1.0 sec slower around the Nürburgring.
The new A45 and CLA45 have a much more comfort-biased spring and damper set-up in Comfort and Sport modes, making them feel more rounded and grown up with no less tenacity when you drop the hammer on a twisty road. The A45 in particular now feels less of a boy racer special, even if the optional track package aero spoiler kit is just as visually extrovert as before.
In terms of soundtrack, no four-cylinder is ever going to raise the hairs on the back of your neck in the way that a good five or six does. That said while the M139 motor sounds smoother and less flat than its predecessor, musicality continues to evade its resume and it remains an effective rather than an inspirational tool.
High torsional stiffness of the body-in-white is a pre-requisite for a good handling car and is something AMG understands very well. Thus another change enthusiasts will notice under the bonnet of the new cars is the three-piece alloy strut brace bridging the suspension towers.
If you were to put the car on a ramp you would also notice the alloy undertray bolted under the engine bay. Apart from helping to close the ‘box’, making the front structure of car torsionally stiffer, this panel also contributes to aerodynamics by smoothing the airflow under the front of the car. Metal fillets reinforce the front longitudinal members just in front of the A-pillars, while at the rear underbody struts increase torsional rigidity in local areas.
As a comment on the increased quality of the second generation compact Mercedes in general it has not gone un-noticed that a pair of hydraulic struts now hold up the bonnet. The low rent manual strut used before had no place on a car costing as much as the original A45 AMG and its siblings!
The new A45 and CLA45 AMG are an impressive pair of high performance compact cars with no peers in their respective classes at this time. While the A45 AMG is the ultimate expression of the hot hatchback phenomenon born over four decades ago, the CLA 45 AMG is an elegant compact saloon with a real sting in its tail.