Your 5.0-litre V8 Mustang too tame? Talk to Harrop.

This is a 2018 Ford Mustang GT 5.0 V8, with a 10-speed automatic transmission. The stock engine delivers up to 339kW of power at 7000rpm and 556Nm of torque at 4600rpm, healthy figures, but the car weighs over 1700kg. And when it comes to muscle cars, there’s no such thing as too much power. That’s why Harrop are offering a supercharger for the 5.0, and I was lucky enough to be the first journo to test the result.

What’s a supercharger?
A supercharger increases the power and torque of an engine by forcing more air into the cylinders. The engine drives a belt which powers an air pump which pushes more air into the cylinder than the engine would otherwise be able to draw in. The greater volume of air in the cylinder means an increase in air density, so the more fuel can be injected to keep the air-fuel ratio correct. And the more fuel injected, the bigger the resulting ‘controlled explosion’…which means more power and more torque.

The particular design of supercharger used by Harrop is the Roots-style positive displacement blower. This means it delivers a near-constant amount of extra air to the engine, as distinct from varying it with engine speed, so there’s more of an improvement in power and torque at lower revs compared to superchargers which increase the air volume with revs. 

Incidentally, a turbocharger is the same as a supercharger except the compressor is driven by the exhaust gases. Both turbo and superchargers are known as forced-induction or FI which reflects the fact air is being forced into the engine, not just drawn in.

2018 Ford Mustang GT Harrop Supercharged V8 review

Let’s first talk about what the Mustang is, and isn’t. Ford’s performance coupe is a muscle car, which means while it’s pretty big it has only two doors and seats just four people, and the two in the back will either be children or uncomfortable, or both. Super practical for the size and money it is not, and there are other cars which handle better, are more liveable and go about as quick for the same money or less – hot hatches such as the Renault Megane, Subaru WRX STi and even Ford’s forthcoming ST.  But, people love the Mustang look, and it’s one of the very few V8 rear-drive cars left, particularly with a manual option, although our test car had the 10-speed auto.

What you do get is a comfortable cruiser, hence the “GT” (Grand Touring) badge on the back, with lots of boot space, lazy V8 power and decent handling. And it’s not so low it’s a pain to climb in and out of.  Sadly, however, the interior ergonomics are disappointing. The right-hand-drive conversion should have shifted the parkbrake from left to right, and the drinks bottle holders from right to left, but Ford didn’t bother and so I found my drinks bottle getting in the way of my left arm. Doesn’t help that the gearshift somewhat obstructs access to the lower switchgear, and the door pockets are too small to be useful. At least the controls are mostly switches and buttons not just touchscreens, and there’s Ford’s excellent Sync 3 infotainment system.

Nevertheless, the Mustang is a good mix between daily drive, performance car, and distance tourer, and the V8 certainly means you can always be entertained by the soundtrack and five-litre acceleration. So why bother to supercharge?

Because you can turn the car from a wolf to werewolf with a touch of your right foot, and there’s no downside. The supercharger delivers around 48% more power and 30% more torque, so what’s not to like! Here’s the dyno graph:

Before and after dyno run. The figures are measured at the hubs, whereas the stock car’s figures are measured at the flywheel so the stock figures don’t match Ford’s published numbers. The percentage increase is what’s important, and as you can see, it is significant and an increase all the way through the rev range. There is also less tail-off at power towards the rev limit, important for a feeling of constant acceleration.

The acceleration numbers haven’t been run, but Harrop’s previous 2016 six-speed supercharged Mustang ran the quarter-mile in 10.5 seconds, so with 10 speeds this one should be quicker yet. For comparison, standard supercars like the Ferrari 488 run it in around 10.6 seconds, a non-sport Bugatti Veyron in around 10.2 and the Nissan GT-R in around 10.8. 

You’ll also appreciate the extra power even if you’re not embarrassing much more expensive vehicles at your local dragstrip, because the supercharged car can now use higher gears for the same result so it doesn’t need to drop down as many cogs for an easy overtake, and there’s the aural delight of the supercharger whine over the top of the V8 roar.

One of the joys of a V8 is, or should be, the delicious feeling of surfing forwards on a wave of torque from low revs, and you kind of lose that a bit with 10 speeds. Standard, the Mustang is prone to play around with the gears a little too much for comfort, but Harrop have remapped the gearshift points so there’s less cog-swapping and more relaxed torque surfing. Another improvement is responsiveness. The standard V8 can be a little slow to react, compared for example to lighter sportscars, but the extra power of the supercharger improves responsiveness a touch and, for me, that’s a big part of everyday driving fun.

So while the supercharged Mustang is a comfortable daily, we are still talking here of a rear-drive muscle car developing north of 500kW…it’s always going to need careful handling if you really want to use that capability because that sort of power will overwhelm the rear tyres of anything less than a dragster. But for me, and I guess most owners, having more power than you have traction is just part of the fun. If you accelerate hard the engine traction control will manage the power delivery and that’s neither smooth nor fun, so you need to modulate the throttle carefully, and ideally select your own gears. Or, switch the electronics off, but you’d then best be able to handle the resulting avalanche of grunt.

The cost of the supercharger is $14,685 fitted and tuned, which means a new beast-mode Mustang will set you back around $83,000 and that’s more kilowatts-for-bucks any other comparable rear-drive GT car, for example the Jaguar F-PACE  or BMW M4, both of which are well over $100k. Cheaper rear-drives are the Kia Stinger; powerful V6, rear drive, but automatic only and five doors, as is the Alfa Romeo Giulia.

The question isn’t whether the supercharger improves the car, because it absolutely does with no downside – well perhaps increased fuel consumption, but no GT Mustang owner is concerned about that otherwise they’d have bought the EcoBoost. I don’t even think it’s a question of whether or not you’d want it, because I honestly can’t imagine any Mustang V8 owner that wouldn’t. Really the only question is whether you want to spend the money or not, and like the Mustang itself, that’s an entirely personal decision.

Just don’t drive the car first, because you may find the decision is made for you.

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Robert Pepper

Robert Pepper