Put your foot down: How to boost your turbo diesel power

Want more power from your turbo diesel? We look at a few of the most popular methods of getting more out of the loud pedal.

Turbo-diesel engines and 4WDs go together like bacon and breakfast. They've been the engine of choice for long distance tourers and weekend adventure seekers alike for decades now, and for a bunch of good reasons.

Their reliability and fuel efficiency are generally excellent, and with the new-school computer-controlled common rail injection systems that are an option on every new turbo-diesel 4WD these days, power and driveability have been increased out of sight too.

However, with this new technology you can forget about your old methods of getting more power out of your engine.

Throw the steam-pipe manifolds and junkyard turbos away, and forget about winding up the fuel pump until she starts to blow smoke and then backing it off a little. These days, getting more out of your high tech oil-burner may be way more complex in operation, but in reality is easier than ever to achieve.

While stock engines may be putting out more than respectable numbers off the showroom floor, throw on some bigger tyres, a ute tray full of camping gear and a trailer on the hitch and you can run out of puff in short order.

But it's not difficult at all to get any lost power back, plus some extra on top, and fuel economy is often increased too. Sounds too good to be true don't it?

Welcome to the new age of diesel tuning. 

Exhausts

Factory dump pipes off the back of the turbo are often the first point of restriction in an exhaust system.
Factory dump pipes off the back of the turbo are often the first point of restriction in an exhaust system.

When a 4WD manufacturer builds their exhaust systems they have a few things standing in the way of performance. The big one is noise, with things like mufflers, diesel particulate filters and catalytic converters all being thrown on to keep things within various countries noise and emission regulations.

Whatever the reasons, factory exhausts are generally pretty rubbish

Then there's the "a penny saved is a penny earned" factor - mild steel, press-bent pipe is cheaper to build than larger diameter mandrel bent stainless steel. A hundred bucks in material savings per truck can add up to some pretty hefty numbers when you multiply it across the numbers sold globally.

Whatever the reasons, factory exhausts are generally pretty rubbish and an aftermarket replacement is one of the first places most people will stop when searching for increased power and economy.

Y'see exhaust gas travels in pulses. As your engine completes a combustion cycle and the piston pushes the burnt fuel and air out into the exhaust manifold, past the turbo and down into the dump pipe. When you have restrictions like press bends, which flatten the pipe through the radius of the bend, or restrictive mufflers, the exhaust pulses can bottleneck, causing your engine to have to work harder to push them out.

Fitting a quality, aftermarket exhaust should be one of the first performance mods done to any 4WD.
Fitting a quality, aftermarket exhaust should be one of the first performance mods done to any 4WD. Roothy's LowRange

By fitting a proper diameter, mandrel-bent (the diameter of the tube stays the same throughout the radius of the bend) system with a quality high-flow muffler and catalytic converter, you're eliminating these pressure bottlenecks and allowing the gasses to flow smoothly out of the tailpipe enabling your engine to develop more power. As it's also working more efficiently the economy is often improved too.

So what diameter should you be going for? For most modern turbo-diesels around the 3.0L mark, a 2.25-2.75in diameter pipe is the go, depending on the type of vehicle and the modifications it's got. For larger capacity engines a 3in pipe may be needed, but really the best bet is to talk to an industry professional to see what'll work best for your particular vehicle and intended usage.

We like to see corrosion resistant materials like stainless (hey, we want it to last!) or aluminised steel, mandrel bends and with an inbuilt bung on the dump pipe for a pyrometer (which we reckon should be mandatory fitment to any turbo-diesel).

With a quality system power gains of around 10% are common, and the engine doesn't have to work as hard to develop its power.

Chips and exhausts

Chip installs are pretty basic, with most only needing less than half an hour to plug and play.
Chip installs are pretty basic, with most only needing less than half an hour to plug and play. Roothy's LowRange

Looking for more than what an exhaust on its own can deliver? The next step is to tweak your vehicle's fuel mapping software.

When an engine is tuned from the factory, it has to be dialed in to suit the worst possible conditions. So crappy fuel, crappy air quality, and crappy service schedules. Unsurprisingly you end up with a pretty, yep you guessed it, crappy tune.

By tweaking certain parameters in the fuel mapping software like injector pulse (how long they're held open for), rail pressure, injector timing and boost levels to name a few, you can significantly improve both power and economy right across the rev range.

The most popular method of doing this is by fitting an aftermarket performance chip. These work in a variety of ways depending on the brand. Some increase fuel pressure at the rail, so for the amount of time the injector is open more fuel can be delivered to the combustion chamber, some work on injector timing, keeping them open for longer increments, some work on several different parameters at once while others (usually cheap no-name brands) simply turn the fuel up as high as it goes. Yes, and how does sir like his pistons melted?

Heaps more power, better fuel economy and no reliability issues - what's not to like?

While there is heaps of conjecture on which chips do what, we reckon you're best served by looking out for units that will not void any factory warranties, do not offer unrealistic power figures, can be customised to suit your individual needs, have good after-sales support and can be provided with a tuned exhaust as a complete DIY package.

Once fitted, expect around 30-40% more power and torque across the rev range and 10% better economy. Fair dinkum, if we were to be given the keys to a brand new turbo-diesel fourby and told to modify it however we wanted, a chip and exhaust package would be right at the top of the to-do list. Heaps more power, better fuel economy and no reliability issues - what's not to like?

Flash tuning

Gleno has had his Disco flash tuned, and now the thing is a deadset fire-breather!
Gleno has had his Disco flash tuned, and now the thing is a deadset fire-breather! Roothy's LowRange

Righto, ECU remapping is a bit newer on the 4WD scene but has been around in performance circles for a long time now, and is well proven as a solid engine mod with up to 80% more power being made available - although going that high on a remote-touring vehicle may not be advisable.

Remember how we said that manufacturers intentionally tune their vehicle to the worst conditions? Flash tuning basically involves taking the existing fuel and timing maps on the vehicle's ECU and reprogramming them for greater torque, throttle response, better economy, smoother power delivery and best of all, reliability is unaffected.

While it takes some pretty specialised knowledge to remap an ECU, the results are well worth the costs.
While it takes some pretty specialised knowledge to remap an ECU, the results are well worth the costs.

Manufacturers themselves do the same thing across model ranges. Top-spec vehicles often come with engines that put out greater power. Often it's not the engine itself that has changed, it's that the guys in the white coats have simply keyed in a more aggressive tune.

It's not a simple or half-hour process like the plug-and-play chips however, usually needing a full day or two at a workshop to accomplish, but the gains are worth it. While power and torque figures printed out on a dyno sheet are one thing, the best thing about flash tuning is the seat-of-the-pants dyno.

Driveability is improved by orders of magnitude and the savings at the bowser, around the 20% mark, make it a highly cost-effective exercise. Arguably the best part however is that a reputable tuner will be able to gain all this extra mumbo and fuel efficiency while staying well within the factory safety parameters, and provide warranty coverage for their work. When tuned to an exhaust system, there's a whole heap of gains and not any downsides. Talk about perfect!

Roothy’s LowRange


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