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It's tempting to fiddle with turbo-intercooled diesels, but we suggest not.


Boys love to play around, don’t they? They buy a perfectly good vehicle and can’t help wanting to ‘tweak’ it.


You know the sort of thing we’re talking about. Before common rail injection and emissions gear was attached to 4WD diesels the common fiddle was a ‘screwdriver tune up’ to get more fuel injected, extractors, a drainpipe exhaust and maybe an LPG torque-topping tank, for a little extra poke on steep grades.

Another favourite was the ‘sticky foam’ air cleaner that was claimed to reduce air intake restriction. The idea with this was that you worked sticky oil into an open-pore foam element and replaced your paper air cleaner with it. Old timers shook their heads, because they could remember oil-bath air cleaners.

It didn’t take long for the foam air cleaner to get discredited as a paper filter replacement on 4WDs: it was a high-maintenance item and when it dried out it didn’t pull dust from the incoming air. It failed ‘open’ where a paper filter failed ‘closed’.

Also, sticky oil migrated up the inlet manifold and made a right old mess, especially in turbocharged engines. Oily foam air cleaners still work well on bikes and small engines where they’re externally mounted and regular re-oiling is easy.

A more recent ‘use’ for the sticky foam air cleaner is as a pre-cleaning ‘sock’ on a snorkel scoop. It may seem like a really good idea, but it isn’t.

If you need some form of pre-cleaner take note some snorkels are fitted with a ‘cyclonic cap’ pre-cleaner and the most common is the one fitted to LandCruiser 70-Series factory snorkels.

This circular device creates ‘swirl’ in the incoming air and the centrifugal force of this swirling air flings large dust particles to the outside of the cyclone device, where they can be ejected manually, or automatically. That’s the only safe, non-restrictive form of pre-cleaner.


The chip

The automotive market is always full of ‘snake oil salesmen’ offering ways to increase power and torque, and save fuel. 

Back when nearly all 4WD diesels were naturally aspirated the performance enhancers pushed turbo kits and, later,  turbo-intercooler kits. Some of these worked very well and some didn’t. People who bought well-engineered kits and drove wisely had good experiences, but many a turbocharged pre-chamber
diesel blew up. Our 2.8-litre HiLux expired with multiple combusion-zone cracks and we had driven it carefully.

Nowdays, all new diesels have forced induction, so the engine hot-up scene has shifted to newer gadgets and heading them all is…the chip or the ‘remap’.

4WD makers who thought the more-than-ample standard power and torque figures of 21st-century turbo-diesel utes would satisfy the new breed of ute owners didn’t understand the passion for fiddling.

In no time we had a wide choice of after-market performance chips. All these void engine warranty, of course, and are probably illegal, from an emissions ADR angle.

We say ‘probably illegal’ with some surety, because we’ve asked several chip makers and ECU re-mappers to verify that they don’t alter ADR emissions compliance. None of them wants to go there, but then neither did some VW and Mercedes-Benz diesel engineers…

Chips and ECU re-maps are available from dozens of sources these days and all of them claim to increase power and torque, and reduce fuel consumption. The fact that these devices increase power and torque is undisputed: any dyno test will prove that.

We’ve tested some chipped 4WDs and there’s no doubt that their performance was excellent.

Fuel consumption improvement is much more difficult to prove. Yep, we have some mates with ‘chipped’ diesels who swear that their economy has improved, but we suspect that has more to do with a change in driving patterns – to produce the claimed result – rather than an inherent benefit of the chip installation.

One even confessed that he found towing at 90km/h produced the best economy, so we wonder why did he bother with an expensive performance-increasing chip in the first place?

Chip makers and re-mappers claim that their add-ons are well within engine design tolerances and can’t do any harm. There is certainly some truth in this claim, but how do the chip designers know what the engine maker’s exact operational parameters are? There is obviously some conservatism in the factory fuel injection mapping, but how much?

Another assurance from chip makers is that their products are warranted against failure. Most chip buyers believe that’s protection for them in the event of an engine failure. It’s not: it covers chip failure. If your engine blows up or suffers serious wear after being chipped it’s your responsibility to prove that the chip caused the failure. Good luck.

Understandably, the engine maker won’t be interested in helping either. Some chip makers and re-mappers claim that ‘enlightened’ engine makers quietly endorse their procedures. We couldn’t find any such ‘enlightened’ engine makers. Fit a chip or re-map the engine computer and you’re on your own.

We’re also very concerned about the fact that all chip makers and re-mappers explain how their systems can’t be detected by a dealer’s diagnostic computer. If there’s nothing to hide, why bother?

One of our mates chipped his diesel manual to give him more flexibility and economy when towing, letting the vehicle run in top gear, rather than needing a downshift on hills. There are at least four downsides to this procedure.

Firstly, the engine is operating at lower than designed revs for the torque/power figures it’s producing and that loads the pistons, rods and bearings with forces that were never foreseen by the engine designer.

Secondly, combustion pressure and heat rise (check your pyrometer if you don’t believe us).

Thirdly, loads on the overdrive gears in the box are also outside design expectations.

Fourthly, water and oil pump (and mechanical fan) speeds are lower.

In most high-load, highway-speed situations a 4WD diesel benefits from running no lower than 1600rpm and 2000rpm is usually better. Heavy truck diesels and transmissions are different, having been designed from the outset to cruise and hill-climb at much lower revs.


Catch cans

The latest fiddlers’ fad is the oil ‘catch can’. Catch cans also void engine warranty, because they’re an interference with the positive crankcase ventilation (PCV) system.

The ads for catch cans make them sound like something new, but they’ve been around for many years, as anyone who’s raced a car knows. Race track scrutineers have always been red-hot on oil drips.

Back before PCV all crankcases vented to the atmosphere. A pipe with a chamfered tip, known as a ‘draft tube’, hung below the engine and dripped condensed crankcase oil mist onto the road.

It was called a draft tube, because the shape of the tip created a pressure drop in the tube as it passed through the airstream, helping suck out crankcase fumes.

(You can tell if a motorcyclist is an oldie when he stops at a red light in the left or right hand tyre tracks, not in the middle of the lane. Before PCVs, the centre of the road was blackened by oil drips and in wet weather that was lethal.)

The draft tube gave way to the PCV system that connects the crankcase to the inlet manifold, directing oily fumes into the engine, where they’re burnt.

The first PCVs originated in the USA in the early 1960s, after the Society of Automotive Engineers concluded that for about $2.00 per car, crankcase vapours could be routed back through the intake, using a spring-loaded PCV valve that’s hardly changed since.

In the case of a naturally-aspirated petrol engine that’s easily achieved, because there’s ample vacuum to suck the PCV tube contents into the engine.

A naturally-aspirated diesel doesn’t have the same degree of vacuum, because there’s no throttle plate, but there is a small pressure drop between the air cleaner and the inlet manifold.

Some diesel engine makers introduced a special valve to enhance this pressure drop and improve PCV performance.

Forced induction engines have enough suction upstream of the turbo or supercharger to allow a PCV system to work well.

So, why is there now a craze for catch cans on turbo-diesel engines?

Let’s go back even further, to the original internal combustion engines. These engines were either naturally-aspirated four-strokes – suck, squeeze, bang, blow – or two-strokes that went only squeeze, bang. In place of suck and blow in the two-stroke was a ‘blower’ that supplied pressurised air to force out exhaust gases and fill the cylinder for the next ‘bang’.

The four-stroke engine wasn’t designed to have forced induction that is commonplace today: a turbo on every new diesel and a turbo or supercharger on many new petrol engines.

Originally, supercharging was a practice reserved for racing cars. Invariably, a supercharged engine had much more output, but was less reliable than a naturally-aspirated one.

Turbochargers came into play after World War II, when modern metallurgy gave us turbine alloys that could withstand exhaust gas heat.

Turbocharged and supercharged petrol engines continued to be used mainly for performance, until the development of emissions regulations from the 1980s. Electronic injection and, more recently, direct petrol injection, in conjunction with forced induction, led to improved emissions and good economy.

Diesel turbochargers sprang from a Volvo Truck development in the 1950s, resulting in improved outputs with less weight and noise, and better economy than larger, naturally-aspirated engines. Today, all new diesels have turbocharging, intercooling and electronically-controlled injection.

Forced induction is a major part of engine developments that have seen outputs skyrocket in recent years. But there’s no such thing as a free lunch and performance increases always come at a cost. Today’s engines are much more highly stressed than those of yesteryear

Brake mean effective pressure (BMEP) in today’s petrol and diesel engine cylinders is around double what it was before forced induction diesels and direct-injection
petrol engines.

This greatly increased pressure challenges traditional combustion zone sealing. No piston, piston ring and cylinder interface provides perfect gas sealing and inevitably there’s ‘blow-by’ into the crankcase.

In the case of a stock engine the engine maker calibrates the PCV system to channel oily mist from the crankcase into the engine air inlet, upstream, in the suction zone of the turbo.

In most cases there isn’t an issue with this system, but there have been some spectacular failures: most notably Nissan’s horrible ZD30 three-litre diesel that was consigned to history when the Patrol departed the scene in late 2016.

In the early ZD30 engines crankcase oil deposits coated the air flow sensor, forcing it to send incorrect fuel demands to the engine fuel computer. Lots of bangs later, Nissan fixed the problem.

‘Chipping’ or re-mapping an engine can increase BMEP even more, encouraging more blow-by and this is why we’re seeing the interest in catch cans. More blow-by forces a greater quantity of oily mist from the crankcase into the PCV system and this oil coats the turbo, intercooler, inlet tract and inlet valves if it’s not trapped en route.

Engine makers don’t fit catch cans, because they’re not necessary on unmodified engines. On a modified engine, with higher combustion pressures, catch cans are high-maintenance items and if they plug with gunk, or the water content they trap along with oil freezes, the pressure buildup in the PCV system can blow the crankcase seals.

Makers won’t warrant an engine that’s retro-fitted with a catch can because it interferes with a calibrated PCV system. Some installations may have a positive effect, but others not.

We checked with a development engineer from General Motors about the need for catch cans on non-competition vehicles and he told me that if GM believed for one second that a relatively cheap part attached to the engine would improve reliability, limit warranty claims and reduce replacement costs, it would have been included in the PCV system.

But then, he was talking about standard engines, not ones that have been fiddled with.


EGR blank off

All new 4WD diesels have exhaust gas recirulation (EGR) systems. To comply with current emissions laws around the world diesel engine makers have had to recycle some exhaust gas back into their engines’ combustion chambers, to dilute the amount of oxygen available for combustion. This technique lowers combustion temperature and that reduces the amount of nitrogen oxides (NOx) that are emitted.

This method isn’t ideal, because it
re-routes carbon-laden exhaust gases through the inlet manifold. This carbon, in combination with the oily mist coming from the PCV system, is blamed for clogging EGR valves and coating the inlet tract and the inlet valves with hard-baked deposits that disturb airflow.

In the case of a diesel engine this oily mess may reduce the efficiency of the intercooler and help plug the EGR valve, but that’s just inconvenient. In the case of a turbocharged petrol engine too much oil in the inlet air may cause premature combustion that can destroy the engine.

In most cases standard diesels don’t ‘coke up’ excessively, but some engines – particularly VW, Audi and BMW diesels – suffer from excessive carbon buildup in their inlet manifolds and on valves. The same mess clogs EGR valves, affecting their operation and compounding the problem.

There are approved procedures for removing this buildup, most of which use a calibrated, pressurised spray of crushed walnut shells – I kid you not – to abrade off the carbon deposits at periodic intervals.

Because of this carbon buildup problem there are many after-market suppliers providing blank-off plates for EGR systems. It’s a sufficiently sophisticated supply chain to have model-specific plates on offer.

Claims made for engines with blanked-off EGR valves include smoother running, improved power and reduced fuel consumption. However, our research indicates that the only measurable benefits are reduced carbon buildup in the inlet manifold and no need to clean the EGR valve periodically.

Before you blank off your EGR or re-map its operation, bear in mind that it’s illegal to do so.


In summary, leave your diesel alone!
































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