Nissan might have lost some loyal customers due to the mediocre reliability of the current D23 Navara (compared to other Japanese utes), but there were no such issues with the previous generation D40. This was also a chart-topping best-seller back in its day (selling over 25000 units in 2012), and still, a worthy car when you consider current prices of new cars. The 2.5-litre diesel in the D40 may be down by a few horsepower from the downsized engine in the newer ute, but that really isn’t a bad thing. It won’t be as stressed, so there’s less to go wrong. Besides you’ll have some spare cash to play with to do a slew of modifications and get those bhp and torque figures up where you want them.
Benefits of an Aftermarket Exhaust
One of those modifications is an aftermarket exhaust. This will have more than a few benefits in the D40:
Improved Designs and Engine Longevity
First, it uses wider tubing than the stock exhaust, which is also set straighter. This allows for an increase in pressure, meaning more exhaust gases exit, and at a faster rate. The setup effectively reduces the possibility of backpressure that can choke the engine of new air. In addition, the transition from high to low pressure means pistons need to put in less work to get the exhaust gases out. The engine is less strained as result, so longevity is another benefit in installing a modified exhaust.
Performance upgrades have to do with the air available for the turbo. There’s more air coming in for the turbine fans, so this spools faster and with more ease. Combine this with a better air take, that effectively sucks more new air in, and you’ll definitely feel the difference. The result is that there’s more than the stock 128kW on offer. Depending on the configuration, and the type of exhaust and intake mods, an aftermarket D40 exhaust can free between 10-15 per cent more horsepower and torque. That’s in line or more than the current D23.
Better Power Delivery
That power is available in a wider rev range. You’ll get more low-down pull or torque, so driving with the tray or tub fully loaded, or with a trailer or caravan at the back is much smoother. In-gear acceleration, say when overtaking, is also improved. The engine can spin freely due to combusted gas going out faster, and more new air coming in.
Modifications are also done to the stock d40 exhaust sound. Replacing complex tubing in the muffler with straighter tubes, in what is known as a muffler delete, lets drivers hear more of the diesel rumble. If you’re after a louder sound then this is what to get. Alternatively, installing better resonators can drone out more noise and vibration, so you’ll forget that you’re driving a diesel.
Lastly, let’s not forget fuel consumption. A less-strained engine means one that uses less fuel to get comparable power figures. There are also lower emissions, as the catalytic converters and DPF filters in aftermarket exhausts remove more toxic particles in the combusted air as it leaves the car. Doing nature a favour is never a bad thing.
Types of D40 Exhausts
There are cat-back, DPF-back and turbo-back exhaust systems for the D40.
Cat-back exhausts are reserved for the few petrol versions of the 6-cylinder engines. These are 4-litre engines sold in earlier D40 Navara utes, and the same powerplant in older Patrols and Pathfinders. Replacement cat-back exhausts remove all the stock parts from the catalytic converter, to the exhaust tips, and often include muffler deletes for a louder sound. Tubing is wider in the mid-section. This helps with the torque numbers that are slightly down on the smaller 2.5-litre diesel, so pulling power is improved.
Aftermarket DPF-back exhausts replace all the parts from the DPF filter to the exhaust tips in the diesels. Tubing is 3 or 3.5 inches along the whole length. This setup can also include a high-flow catalytic converter for reduced emissions, and the usual muffler configurations, with or without resonators.
Turbo-back D40 exhausts replace all the stock parts. This can include an exhaust manifold extractor to regulate increases in pressure, as well as dump pumps to remove excess gases in the mid-section. Turbo-back systems offer the best overall performance and efficiency gains, but do come at a slightly higher cost.
What to Look for?
Go for Aussie made exhausts. They’ll use quality high-grade treated steel that is mandrel bent to allow for the best possible gas flow. This ensures gentler bends in the tubing than your stock exhaust. Heat resistant coatings help to keep the pipes intact when driving through water and mud, so corrosion is not an issue. Individual parts have high-quality joints, that reduce vibration and improve structural integrity. Kits are easy to install, fit in the underbody recess that houses the stock exhaust, and are fitted with bolts. When buying, ensure that you get the right exhaust system for the engine in your D40.