A supercharger makes everything better, right? We drive Harrop Engineering’s 400kW/735Nm Supercharged Patrol. Hang on.
The Nissan Y62 Patrol was revealed to the world back in 2010 and was, we can see now, a vehicle ahead of its time. In Australia, the Patrol faithful hated it for at least three reasons; it had no live axles, no diesel power, and it was deemed too big, despite the fact it’s shorter than most dual-cab 4x4s.
These days, there’s an increasing awareness that modern diesels are overly complex, and the relative simplicity of a petrol is becoming ever more attractive. The Y62 is also, we all now agree, a better off-roader than the revered Patrol GU, and many feel it even outperforms even the mighty LandCruiser LC200 (notable exceptions being, of course, LandCruiser owners). And slowly but surely, fully independent suspension is viewed less and less as the work of the devil and accepted as an effective off-road platform.
The Y62’s strength has always been its powerful V8 engine: 298kW and 560Nm and 0-100km/h in about seven seconds. But, can you ever really have too much of a good thing?
Enter Harrop Engineering. Harrop has a history going back more than 65 years and it’s been wrenching performance cars ever since Ron Harrop bought Norm Beechey’s FJ Holden for $29 and turned it into “Harrop’s Howler”.
Taking a stock Y62, Harrop has fitted a TVS2650 Roots positive-displacement supercharger to the V8, boosting power and torque to around 400kW and 735Nm. But numbers only tell one part of a very complicated story.
So let’s start with what a supercharger is and does. A forced-induction (FI) system is all about forcing more air into the engine for more power, as distinct from an NA (naturally aspirated) engine which draws air in at ambient pressure.
The FI principle is simple; engines need a combination of fuel and air in a prescribed ratio, known as the “mixture”. The fuel is ignited and the resulting “explosion” (more of a controlled burn) forces a piston down the cylinders which turns a crankshaft and ultimately the car’s wheels. The more fuel you ignite, the bigger the explosion/burn and the more power you get. But, the fuel:air ratio has to remain the same. So, if you want more fuel, you also need more air. And that’s where forced induction comes in.
In the case of Harrop’s TVS2650 supercharger, the kit features a cleverly designed water-to-air intercooler system that incorporates aluminium cores within the intake manifold. These cores have separate coolant circulated through them via a dedicated 12V water pump, which in turn transports it to an external heat exchanger (radiator) which sits forward of the Y62’s radiator. Air is drawn through the heat exchanger and cooled by around 50%; this has the effect of making it denser, so more air can be packed into a given volume.
The TVS supercharger is an air pump that then flows the air into the cylinder under pressure – around 8.5-9psi in the case of the Y62s. The rotor group is driven from the crankshaft by a pulley and each revolution of the rotor pack displaces 2.65L of air into the engine.
The diameter of the drive pulley dictates the speed of the rotors, and therefore the flow and resulting pressure of air forced into the cylinder. So, the bigger the pulley wheel the slower the rotor speed and the less pressure (boost) created.
The trade-off with more pressure is the air is compressed and as air is compressed it heats up and expands, reducing the density, which is why the cooling effect of the intercooler is critical.
To match the extra air being fed to the cylinders, the fuel pump was modified, via a larger piston and sleeve, to deliver more fuel. That’s the mechanicals out of the way. Harrop’s engineers then had to tune the ECU (Engine Control Unit).
Because the engine is getting more air and fuel, the ECU’s idea of what an appropriate amount of air and fuel is has to be altered, otherwise errors are thrown as the ECU thinks limits are exceeded. The ECU also calculates torque figures from parameters such as engine rpm and throttle pedal position.
With a supercharger there’s more torque for a given RPM and throttle position, so the ECU needs to be remapped. If that doesn’t happen, the ECU thinks there’s, say, 200Nm of torque when in fact there’s 250Nm, and gives other systems the wrong information. For example, the torque convertor might be designed to lock up at 200Nm, and if it tries to lock up at 250Nm (thinking it’s 200Nm) then it’ll slip, fail and throw an error.
Engine knock is another tuning point. Knock is when the fuel:air mixture in the engine’s cylinders is not fully ignited by the spark plug, parts of the mixture might ignite separately; that’s at best inefficient and at worst catastrophic for the engine and your wallet.
Knock is detected by comparing ignition and non-ignition combustion sounds, which the ECU expects to sound different in specific ways. Now, with a supercharger the engine and combustion sounds are different to a naturally aspirated engine. And that means the ECU will pick up the difference and possibly wrongly attribute it to knock. So, the ECU needs to be taught a new normal.
Of course, there’s much more to tuning an engine than this, but you get the idea and why terms like “bolt-on” do not do justice to all the design and engineering that goes into a supercharger kit. Drag races are a great way to show performance differences, but nothing beats a dyno for simplicity. Take a look at the graph below:
The two blue lines are power, and the two green lines are torque. The thicker lines are the original car, and the thinner lines are the supercharged Nissan Patrol. The figures are in lb/ft and hp instead of Nm and kW, and measured at the wheels of the car so due to the transmission gearing there’s a torque increase and corresponding power decrease compared to the crank figures and both power and torque are sapped because of energy losses through the transmission.
However, that doesn’t change the point of the graph which is to show the differences between standard and supercharged. You can see there’s significantly more torque all the way through the rev range and more power too. It’s not a peaky torque curve either; there’s that supercharged advantage from being belt-driven direct off the crankcase as opposed to a turbocharger needing to wait for increased exhaust gases before it can do its work.
The peak figures for a stock vehicle are 298kW and 560Nm, and translated back to crank figures from Harrop’s hub dyno with an allowance for 15% driveline losses, an estimated 400kW and 735Nm for the supercharged Nissan Patrol.
That’s a lot of theory, but how does that work in the real world? To find out, I spent a few days with Harrop’s supercharged Nissan Patrol and, as a benchmark, borrowed a friend’s brand-new Y62 so I could compare apples with apples.
Besides the supercharger, the other difference between Harrop’s Y62 and a stock vehicle is that it runs 35-inch Toyo Open Country R/T rubber, which are not only a greater diameter and wider but heavier construction and thus greater rolling resistance.
As you’d expect, the bigger, heavier tyres have taken the edge off the performance relative to the stock tyres, yet, floor the throttle and the supercharged Patrol still feels a lot stronger than a stock Patrol. And that’s what you’d expect from the dyno figures.
In the week before I borrowed their Patrol, Harrop ran a 0-100km/h test at Sandown, recording 6.6-seconds for their car and eight-seconds for a non-modified (engine) Y62 also on 35-inch off-road tyres. Watch the video below.
More than being quicker, the supercharged Nissan Patrol also sounds throatier than a stock Patrol, thanks largely to Harrop fitting a new muffler which while currently only a prototype, Harrop said it was happy with the muffler and it would be on the market “very soon”.
When you increase the power and torque your vehicle makes, other changes need to follow like the gearbox shift pattern. Modern vehicles “manage” torque, meaning they limit torque outputs in low gears and reduce torque from maximums in order to change gears, then ramp up the torque again.
Because a supercharged engine produces more torque than standard, the drop from maximum to the point where the transmission will shift is greater, and takes longer. Similarly, it takes more time to get back to the maximum torque, and the result is a gear shift that appears to take longer.
At around town speeds and on anything other than high throttle settings throttle, the transmission is fine and feels no different to how the seven-speeder behaves in the stock Patrol. You’ll only notice the longer shift when you’re at high or full throttle, say, flooring it from the traffic lights or running it down the drags. And bear in mind this is still very much a development car.
There are also a number of subtle cosmetic changes designed to create the impression of overall difference without the changes necessarily jumping out at you individually. Obviously, the wheels and tyres catch your eye… Harrop got Eye Candy Motorsport to black out the Y62’s chintzy chrome and, at the same time, got rid of the fake wood panelling, which exactly nobody likes. It’s all come together very nicely.
Like the sound of a supercharged Y62? The kit is available now from Harrop Dealers nationwide with a drive-in, drive-out price of around $16,000 along with optional powertrain warranty for those that want increased peace of mind.
If you tow, do a lot of sand driving, or just enjoy the occasional trip to the drags, then this thing makes a lot of sense. And the kicker is even after you’ve bought your top-spec Patrol and spent the $16k on the supercharger it’ll still be cheaper than a LandCruiser. And it’ll be a hell of a lot quicker too.
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