The best engine type for a 4WD is a diesel. No contest.
Diesels Belong Everywhere
In fact I'll take it a step further and say the best engine type for any car is a diesel. Pretty soon we'll see diesels in widespread usage in motorcycles too, for an ATV it's a natural fit, road bikes probably a specialist niche, it's just a matter of getting the mindset right, informing consumers so they can make the right choice.
Why are diesels so good? It's all about torque and fuel efficiency, not to mention reduced CO2 emissions.
It's All About Efficiency
A petrol engine is not a particularly efficient power source. Out of a litre of fuel comes only 20-30% of energy produced (this will vary marginally according to the sophistication of the maker's engine technology). That's not a particularly good outcome when it comes to putting your hand in your pocket, week in, week out to fuel up your vehicle. Expensive, expensive, expensive. Diesels on the other hand produce around 40-50% efficiency, a huge improvement and it translates on the road, in significant fuel savings and ease of driving, especially off-road.
Beware The Scammers
Now traditional diesel nay-Sayers will point to the increased cost of purchase of the diesel engine compared to a petrol in a maker's line-up being a major disincentive, the cost difference having to be overtaken before the efficiency benefit starts to pay. It depends on the maker, as some have put a premium on their diesel offerings. A cynic might think that we poor consumers are being taken for a ride, a crude profit ploy to bolster revenues, surely not? Sadly yes. Whilst some makers have been keen to get bums on diesel seats and to their credit at no price premium, others have charged exaggerated amounts for the diesel experience. In plenty of 4WD brochures today though you'll find vehicle makers have ditched the petrol option completely so it's a no-brainer. Diesels rule OK!
Remember This Acronym... CRD
Ever since the advent of common-rail, full electronic fuel injection (direct), coupled up to a turbocharger and intercooler, the negatives attributed to diesels in the past have largely vanished into thin (cleaner) air.
The Common Rail; electronically controlled fuel injectors dispensing fuel in precise quantities under extreme pressure from a "common rail" or manifold.
Rattly No More!
Diesels of a decade ago were pretty forgettable, non-existent acceleration, rattly, smelly, and plenty of unhealthy exhaust particulates. Naturally aspirated (non-turbo), indirect-injection motors were the worst offenders and Japan produced plenty of them. Their old-fashioned fuel pumps weren't particularly good at metering fuel in exact quantities and a lot of the time over-fuelling occurred. That was the black smoke you'll still see on older diesel vehicles coming out the exhaust pipe. These same vehicles were pretty dangerous on the highway too, as you had to plan an overtaking move kilometres in advance, but not anymore, don't bother dropping a gear, just mash that accelerator pedal, hang on and ride that sweet seam of torque.
Where's Your Torque Hiding?
With a petrol engine, maximum torque is typically found pretty high in the rev range, 3-5,000rpm whilst a diesel gets cracking from just off idle, and peaks at around 2,500rpm. In every driving situation that translates into fuel-efficient motoring. There's simply no need to rev the vehicle out beyond that point. Use the gearbox, hit the torque peak and go up a gear. Lots of 4WDs are running six-speed gearboxes these days, so it's easy to find yourself at the highway limit barely ticking along at 2,000rpm. Lower engine speed means less fuel used. Off-road it means that you can pick your way over obstacles at a snail's pace, minimising the damage potential to the vehicle and the track.
Big Is Better... I Don't Think So
There's also been a reduction in engine size over the last few years. As the fuel systems have been refined and more and more torque extracted, engine capacity has come down. Mitsubishi until recently used their 3.2 litre diesel in the Pajero and Triton which topped out at 373Nm, a pretty good number. It's been replaced with a newer 2.5 litre that produces over 400Nm. Volkswagen will have two diesels in their line-up for their new Amarok ute range, a 2.0 litre and a 2.5 litre. Both boast impressive torque outputs and fuel consumption around 8L/100kms. I've been driving a 2.5 litre Navara for the last three years. With 400Nm it's a hoot and cheap as chips to run. It's simply a case of less is more.
Go Double The Distance
If you're still not convinced, the quoted fuel consumption figures you'll see on websites for different vehicles are often understated. From my experience driving like for like vehicles, petrol versus diesel often shows a greater disparity than the 10-15% advantage they quote. I've seen diesels often do double the distance, especially off-road.
If you do the research even further and investigate “cradle to the grave” costs, the cost of manufacturing the vehicle, the value it generates whilst in service and longevity, diesels win hands-down. Diesels that get plenty of TLC (clean air, clean fuel & clean oil) will happily run up hundreds of thousands of kilometres before they need a spanner turned on them, try that in a petrol!
Europe Leads... The Rest Of The World Should Follow
For passenger cars Europe has led the way for ages. Small and efficient vehicles have been scurrying around European streets barely sipping fuel for decades using tiny diesel motors. Again the beauty with these motors has been torque and fuel-efficiency, coupled up to a body mass that's light, equates to zippy transport. Toyota has gone down a different pathway with the Prius and now the locally made Camry petrol hybrids.
Here's a couple of new AWD diesels compared to Toyota's Camry & Prius Hybrids. Remember the AWDs are in a different vehicle category, heavier and with greater carrying capacity, not passenger cars as are the Toyotas yet produce similar fuel efficiencies. Partner up a hybrid driveline with a diesel engine and surely you've got the planet's best powerplant for an energy hungry planet?
BMW X3 - 2.0 litre 4 cylinder (380Nm), 149g/Km CO2 levels, 4.7l/100kms = 60mpg
Volkswagon CrossPolo - 1.6 litre 4 cylinder (230Nm), 113g/Km CO2 levels, 4.3l/100kms = 65mpg
Toyota Camry Hybrid - 2.3 litre 4 cylinder (187Nm) petrol/270Nm electric, 142g/km CO2 levels, 6.0l/100kms = 47mpg
Toyota Prius Hybrid - 1.8 litre 4 cylinder (142Nm) petrol/207Nm electric, 89g/km CO2 levels, 3.9l/100kms = 72mpg
By coupling up a small petrol engine to an electric motor they argue that significant fuel savings can be had without sacrificing any sensation of power. Electric motors are good sources of torque, petrol not so. But what if you were to couple two good sources of torque?
Hail The Holy Grail... Diesel Hybrids Are Coming
I'm confident that storage will improve dramatically over the next few years as battery advances are made, so the range whilst running purely on electric power will increase. But I can't wait for the day when we're offered a real alternative and auto-makers offer diesel hybrids. Imagine that, a small diesel that'll already average 3-4L/100kms with 300Nm of torque, coupled up to an electric motor that boosts the combined torque figure to 500Nm or more and provides a cruising range of 2,000kms before it needs refuelling? That truly would be exciting.