What do you do with a 306kW V8? If you’re Harrop, you add a supercharger. We drive the 2017 Harrop Ford Mustang S550 GT TVS2300…

THERE IS something to be said for the purity of a large-displacement V8 without forced induction, especially now that in today’s age of strict emissions such engines are becoming rarer and rarer. Ford even told us at the Mustang launch last year that a hybrid Mustang could well be a reality in the future.

However, there is also something to be said for increasing your Mustang’s engine output from “a lot” to “yeah!”, and this is clearly the view of aftermarket performance specialist Harrop. So, let’s take a quick look at what they’ve done and how.

The first modification is a supercharger, and that works quite simply; 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 more air in the cylinder (increase in air density), 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.

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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 greatly with engine speed.

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.

Harrop have also engineered a cold air intake, or CAI. This is a replacement air intake designed to suck in cooler air than the standard intake. The reason is that cooler air is denser, and therefore you can fit more air inside the cylinder, and just like the supercharger, the more air inside the cylinder, the more fuel you can inject to keep that air-fuel mixture ratio constant, the bigger the ‘bang’ and the greater the power.

There’s also an improved exhaust, a 3-inch catback, mandrel-bent, hi-flow, bi-modal unit. The ‘catback’ means it’s all-new from the catalytic convertor backwards, the 3-inch means it’s three-inches in diameter, mandrel-bent means it’s a constant diameter through the bends (good for the exhaust-flow aerodynamics) and bi-modal means it can alternate between being quietly rumbly and king of the jungle roary.

The bi-modal sound system works via vacuum diaphragm valves actuated by engine vacuum through solenoids controlled by a control module referencing engine and vehicle data via the OBD2 port. The parameters for valve opening are set via a phone app. Variations include full range of RPM, full open, full close and cruise mode, so you can set how your exhaust works.

Sound is one thing, but why do exhausts increase power? It’s actually more that they reduce power losses. The exhaust gases need to be pushed out of the engine with minimal effort so ideally, the exhaust pipe would be about an inch long, and job done. However, for safety, sound and emissions reasons we have long and complicated exhausts with things like mufflers and catalytic convertors. All these things have a job to do but they all make it harder for the exhaust gas to be pushed through, and that saps engine power. Aftermarket exhausts are designed to allow the exhaust gases to flow more freely, so more power goes to turning the wheel and less is used for shoving gas out the tailpipe.

So much for theory. The standard V8 Mustang has 306kW at 6500rpm and 530Nm at 4250rpm, weighs around 1750kg and runs 0-100km/h in about 4.8 seconds. Those power and torque figures are from the manufacturer at the flywheel, and for the stock car that changes to 255kW and 490Nm at the hubs as measured by Harrop on their in-house dyno. The “at the hubs” figure is used because the “at the wheels” is a near pointless measure for reasons we will explore another time.

When the exhaust, CAI and supercharger are added we arrive at a figure of around 445kW and 655Nm at the hubs, or around 74% more power and 34% more torque. You could say that’s a worthy increase, and it should be viewed as a maximum as the exact figure depends on the engine control unit tune and amount of pressure you want the run the supercharger at – it usually runs from 6psi at 2000rpm to 8.5psi at 7200rpm.

What’s the Ford Mustang S550 GT TVS2300 like to drive?

We went for a spin around Sandown Raceway in Victoria to find out…

When I reviewed the Mustang at launch back in early 2016 one of the notes I made was that the 2.3 lacked a bit of throttle-response immediacy, and while the V8 was better it wasn’t in the same ballpark as say an 86 or MX-5. It had the power, just not the quickness of response, as indeed you’d expect from a larger, heavier car.

Now, with the power upgrades from Harrop two things change. You do now get that immediacy of response… firstly, because there’s more power, and secondly because Harrop has remapped the throttle and gearshift. It’s still a big, heavy car but now one that is more enjoyable as it reacts quicker. Superchargers are typically a bit better in this respect than turbochargers as the supercharger is driven directly off the engine so it doesn’t need to wait for exhaust gases to build up like a turbo does.

And then there is the extra power. Lots of extra power! The Mustang now just pulls, and pulls, and pulls. You go past 100, 150, 200km/h… and even then it’s still piling on the speed. It’s thrilling and intoxicating in a way the standard car can’t match, and it’s not just the power either.

The bi-modal exhaust is worth the coin for the full-throated, meaty roar…it turns heads from pitlane! There’s no sound playing through the speakers here, no trickery, just the direct and pure aural sensation of a real V8 doing what it does best. It’s the sort of sound that converts young boys into lifelong petrolheads. Sadly, the modern era of hybrid is never going to evoke the sort of head-turning, heart-quickening roar of authority you get from a V8.

So how quick is it? The car has run a 10.5 second quarter-mile (watch the video), albeit with gearshifts set for drag racing meaning abrupt and quick. For comparison, standard supercars like the Ferrari 488 run it in around 10.6 seconds, a non-sport Veyron in around 10.2 and the Nissan GT-R in around 10.8. So for straight-line performance and sheer awe I am giving this car 10.5 out of 10.

The power is great, but when you’re accelerating over 200km/h the time will come when you need to stop, something many modifiers overlook. Pretty much every stock car will overwhelm its brakes at a racetrack, particularly the heavy and fast ones like a V8 Mustang, and even more so when you up the power by double-digit percentages. So I was pretty happy to see the upgraded rotors on the Harrop Mustang, and even happier to feel the responsiveness and reassurance when I touched the brake pedal. I wouldn’t go the supercharger without the corresponding improvement in braking. The pads and calipers were standard, but I reckon track/street pads and upgraded fluid wouldn’t go amiss.

Quite impressive is the fact that the unsprung mass of the brakes has been reduced by 30%. Unsprung mass is the mass that isn’t controlled by the suspension – for example brakes, wheels and tyres. Reducing this mass improves handling as the suspension is able to respond more quickly as there’s less inertia to overcome when bumps are hit or weight is transferred from side to side. The mass reduction has been achieved by alloy hats – that means the rotor is two-piece, with the inside piece made of alloy and the actual part the pad grips still being cast iron.

There are also wider tyres. The stock V8 runs 255/40/19 front and 275/40/19 rear (yes, greater diameter at the rear than the front) and the Harrop car runs 275/35/20 at the front and 295/30/20 at the rear.

Now for the corners. Looking back on my stock test which included some racetrack work, I noted that the Mustang handled well enough, but as you’d expect lacked the agility, responsiveness and feel of smaller, and lighter cars, more of a point and burn sort of experience. I did note the V8 could be readily steered on the back axle with a little throttle, and it was generally fun as most cars are on racetracks.

This particular Mustang is different. You’re not hurting for power, or for brakes, but it’s what it is in between that needs some development. However, this is a test car and Harrop were in the process of dialing in a brand new suspension package and gearshift programme. So the car wasn’t particularly confidence-inspiring into, through or out of corners – you feel a bit disconnected and unsure of limits – but we’d expect that to be sorted out as part of the development programme. The fun of the car is in the straights, not dancing it through corners.

The other modification of note is the interior, which has some tastefully applied Alcantara, including on the steering wheel. Doesn’t make a big difference, but I kind of like that… a bit subtle, not in your face.

So should you look at a supercharger for your Mustang, and maybe the exhaust? I’d definitely go for the exhaust as half the fun of a V8 is the noise, and if you have the coin then the supercharger would certainly improve the vehicle, particularly if you take it to the track. And if you do, then you’d best budget for those brakes!!!

Pricing

• Ford Mustang V8 automatic $65,000 (approx. driveaway retail price);
• Supercharger, Cold Air Intake, Full Exhaust System & Tune – $19,279 fitted;
• Forgeline Wheels – Custom built to order, approx. $2200 per rim;
• Truetrac helical gear LSD Differential- $3069 fitted (the Mustang does have a standard LSD);
• Shockworks Suspension – $3300 fitted;
• Rotor Upgrade – $4100 fitted; and
• Full Alcantara Interior Package – $8800 fitted.

Total accessory price: $47,348 (excl wheels)

Price as tested: $112,348 (approx.)

Further reading

• Ford Mustang V8 and Ecoboost road test