Truck tech: big-block engines

In a world of miniaturisation, fuel efficiency, digital engine controls, advanced metallurgy and alternative fuels, the old adage that 'capacity means capability' still rules in much of Australia's heavy-duty transport sector. For all the engineering poured into the 13-litre engine class, it's the big-block 15- and 16-litre engines that the kings of Australia's highways, with little prospect of their reign ending anytime soon.

Electronic engine controls have brought these giant engines to a level of efficiency that many car engines can't achieve. The cheapest way to move tonnes of supplies lies simply in using the biggest truck legally permitted to use the roads.

Complementary advantages in aerodynamics, tyre technology and fuel formulation continue to improve performance to the benefit of operators, consumers and the environment. Blending all of these factors underlines the fact that it's the horsepower at the tyres that counts, not at the flywheel. But the engine is the heart.

These engines move everything from hamburgers to houses, across the city and the continent, on bitumen and dirt 24/7. The reliability is generally outstanding, and Australia has a well-drilled network of service support to keep the rigs mobile and delivering on time. Rarely do perishables perish and few deadlines are missed, due to the inherent reliability of the biggest engines in Australian trucks.

They are made in Germany, the USA, Sweden, and Japan, and most are a blend of technology and engineering from development teams dotted around the globe.

We've looked at the current engines available and lined up their individual assets. There are some surprises and, of course, most are available only in one brand of truck. But as long as some fleets buy the engine before they pick the truck to wrap around it, this comparo may help to accurately target task to performance, saving both capital expenditure and whole-of-life cost.

Let's take a look at the main players…

CAT
Not many years ago, a tough task meant, "It'll need a CAT to do that job." Then Caterpillar in the US made a mind-bogglingly stupid move. They canned sales to on-highway manufacturers with no notice (and even less logic).

Thankfully the C15 is now back, but you can only get it nestled in the bowels of a CAT truck. The specs and output have remained pretty much constant, as additional development has focused on emissions control. Meanwhile the opposition has strengthened, so now the C15's 550hp is the lowest of the group, and even its legendary pulling power is out-torqued by eight of the 12 contenders.

Its key advantage is simplicity, with the C15 dispensing with any on-engine emissions paraphernalia. All the emissions compliance is completed in two Diesel Particulate Filters (DPFs), one in each exhaust line, and the filters are there for the life of the engine. You can't get a simpler solution than that.

My last drive was a bit of a disappointment, as the engine was pulling well below expectation, but in that case some turbo plumbing leaks were discovered post-drive that would have impacted on power. Most importantly, owners are delighted with the C15 and look like staying with the brand. That's always a good sign.

CUMMINS
The biggest seller in this game, the Cummins ISX/Signature range, has the second-smallest cubic capacity but the biggest power and torque figures of all the US engines (except for Mack, which is a US variation on the Swedish Volvo theme anyway).

There's one block, one architecture, one top-end and one fuel system. But change the engine software and the ISX at 2508Nm becomes a Signature at 2779Nm.

I experienced the difference on a run up Cunninghams Gap a few years ago. Two Macks, same load and identical horsepower, but mine had the extra 271Nm. I hit the bottom about a kilometre behind my mate and caught him half-way up. Being a grandstander, I pulled out to overtake, missed a gear and ground to a halt before I could sort out the Roadranger! Laughs all round and I still haven't lived it down.

Both are now available in either EGR (Exhaust Gas Recirculation) or SCR (Selective Catalytic Reduction) emissions systems, which suits the fleets that chose their course a while back and set up maintenance, support, driver training and AdBlue tanks to suit.

The EGR runs hotter and uses a VG (Variable Geometry) turbo, while the SCR has a waste-gate set-up.

Cummins impressed the industry with the way it handled a turbo issue a few years ago. It cost the company some business and a lot of warranty work, but the engines remain popular with the big-distance 24/7 fleets that run up over half-a-million kays or so each year.

Some oil leaks have appeared on the EGR engines but they are being dealt with under warranty in the characteristic 'face up to it and fix it' Cummins style.

The SCR versions drop 79kg from the front axle, but put it back (plus a bit more) on the chassis in the form of a full AdBlue tank. However, it's further back from the front axle and is a diminishing load anyway.

DETROIT DIESEL
I'm not quite sure why the DD15 is here instead of the DD16, but decision-makers at Detroit seem to be comfortable with the DD15's performance on Aussie roads. It's the smallest capacity at 14.8 litres but it has almost identical output to the CAT C15. But it's a very complex engine which in my experience runs hotter than most.

Detroit's main claim with the DD15 is that you pay for fuel for 500hp, while the turbo compounding gifts you an extra 60hp from the exhaust stream. It's a good line, and seems verified by the records. The DD15 is the best on fuel of the Americans and its B50 life (the point at which 50 per cent of any given engine type will require a major repair, overhaul or replacement) is hard to beat.

However, the high ambient temperatures here are bringing some problems to the fore. There have been a series of oil leak problems, and a major camshaft change has altered the sound of the engine significantly.

I think that's a good thing. I left the Daimler Trucks HQ in Mulgrave a few years ago in a new Coronado B-double bound for Adelaide. Pulling out of the gate, the driveline sounded as though a box of nuts and bolts had been dropped in the sump. I nearly pulled over and stopped, thinking there'd been a massive oil loss. But while looking for a place to pull over, I noticed the sound easing off, and after around 20 kilometres the engine note settled down and the truck sounded as it should.

Interestingly, Western Star presently appears to have the most DD15 difficulties, even with one of its award-winning show trucks that is running around 5000 kilometres each week.

Freightliner has a lot less, and that could be because of major cab changes engineered at the factory for Australia-bound trucks to improve airflow through the radiator and engine compartment. We're talking a rise of 50mm between the cab and the frame just for ventilation.

ISUZU
Isuzu is the Japanese builder of choice for a wide range of diesel engines in applications from truck, marine and stationary power. In fact, the 6WG1 block appears in all three – producing up to a hefty 500kW (680hp) in a medium-duty maritime role.

That means it's rated to deliver that power for up to six hours continuously, with a maximum of 3000 hours in a year. Only Mack (Volvo too), Mercedes-Benz and Scania have a larger capacity, but all except for the Mercedes-Benz V8 are quite a bit heavier.

The TCS version used in Isuzu's heavy trucks has been refined over several emissions control evolutions, but remains best suited to a vocational role rather than linehaul work. It has the lowest power and torque output in this group, and the torque peak is at pretty high revs – 1200rpm.

Tied to a pretty lazy AMT transmission, the Giga prime mover or rigid doesn't set the world on fire, but is popular within its customer base as being reliable and therefore totally dependable.

We're looking for a new engine design soon, which may be similar to the 6WFi currently sold in the Giga overseas.

MACK
If ever there was evidence that engine mapping and fuel system mods can completely change an engine's characteristics, Mack's MP10 is it.

The US version of Volvo's D16G feels and sounds a polar opposite to its twin brother, and some of that's due to the truck design – cabin, floor, insulation etc. But the Mack is popular for the hard slog of road train, stock transport and heavy haulage applications. Tied to the mDrive AMT it's a breeze to drive and highly cost-effective.

This combination changed my driving style. I left Port Augusta in a Super-Liner 685hp with the mDrive box, pulling a triple north towards Darwin. Setting off the 'box skipped from second through to 12th with only four changes – fully loaded.

The big engine worked right through the impressive torque band and pulled hard from 1000rpm. A Mack engineer in the US admitted to me that the company had engineered more noise into the big Volvo design so it sounds more like a US engine and less like a Euro donk. Whatever the changes are though, it adds 100kg to the weight of the green-painted version as installed in the parent brand.

MAN
MAN's new D38 is due to land in Australia very soon – in fact evaluation trucks are already in the country and being prepared for a testing program. But we only have spec details from the overseas release and various parameters and outputs may be slightly different.

The engine is MAN's latest and packages a lot of fuel efficiency technology into the injection and turbo system. At this early stage, it appears to be leading its competitors in the ability to squeeze energy out of diesel fuel.

MERCEDES-BENZ
Benz's biggest is one of the last V8s in the line-up, and it will be superseded by the new in-line six currently powering the Actros in Europe. The V8 is from Merc's modular days. Either the V6 is the OM 502 with a couple of pots cut off or the other way around but, however it happened, it made sense for parts and service savings, technician training and of course weight savings.

At 15.9 litres it's smaller than the other Europeans but bigger than all the US engines. From an efficiency point of view, it develops the most Newton-metres per tonne, except for the Swedish flagships. If you are seriously pressed for tare weight, the Merc is for you – its nearest competitor is 96kg heavier.

SCANIA
Scania offers two engines at this level. The first is 15.6 litres and it's a cast-iron V8. It's available in a range of power ratings and the lowest one is often chosen by customers who could get by with a 13-litre engine, as it means less stress and therefore less wear. Scania has a top-tier fuel efficiency reputation, so under-utilising an engine's power and torque really does spell greater fuel efficiency.

Scania's second engine entry is a special. It exists as a result of a 'mine's bigger than yours' piddling contest with Volvo. It's cast in compacted graphite iron, has a capacity of 16.4 litres and churns out a thumping 730hp. But the torque figure initially seems like fiction – 3500Nm at just 1000rpm.

I've driven this beast on hills and it is truly unstoppable. In fact there is so much torque, that the engine management system de-rates the grunt by 200Nm up to ninth gear.

The engine construction allows Scania's XPI extra high-pressure injection system to boost injection pressures to 2400 bar without thickening the cylinder walls. But it's still the heaviest of all the engines at 1405kg, meaning axle limits need to be considered when bolting accessories on the front.

VOLVO
The Volvo D16G engine probably generates more confidence among drivers, owners and fleet managers than any other linehaul powerplant. My experience in both heavy traffic and on the open road has been the same – quiet, easy to drive, responsive and seemingly unburstable.

The engine development was shared with Mack's people and a lot of engineering decisions were taken at Volvo tech centre at the Renault campus. It's a truly world design and allows a wide range of mapping to suit fuels, climate, terrain and usage.

It generates the most horsepower per tonne and is only bettered by Scania's monster for torque.

THE CASE FOR LOCAL INPUT
Back in May 2013 one of the biggest players in the on-highway truck engine market released an update of its top-selling product. The brand doesn't matter for this story, but it highlights the nuances of Australian road conditions and the need for fine-tuning to suit. Manufacturers who assume that a truck or an engine that performs in other markets will do the same in Australia are living dangerously in terms of customer loyalty.

This engine was treated to changes that improved fuel economy, enhanced driveability and reduced noise. Better throttle response at the pedal meant increased driver satisfaction and feedback that suggested the engine was 'performing better'.

Some other modifications related to conditions that had appeared in other markets but much later in the ownership – Australian conditions saw the issues emerge sooner.

Engineers replaced some components, changed assembly procedures in others, and redesigned the camshaft to improve Jake brake performance.

The addition of two more sensors, a water-in-fuel sensor and a low-pressure fuel pump sensor, improved maintenance planning and preventative care.

In short, the ongoing modifications underline the close attention manufacturers now give to keeping trucks on the road instead of in the shop. High technology is all very good, but high-intensity oversight by the builders is better, as the benefits of new materials, new processes and tighter servicing care pay big dividends to the bottom line.

The most interesting point is this: before the above changes, the engine already had one of the best reliability records on the market. Now, its B50 life is at the top of the game, at 1.9 million kilometres.

Clearly, none of the engine builders seem content to sit on their laurels, and that equates with major savings for operators.

15/16-litre engine specifications comparison: