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Engine Management for Turbo Conversions - Part One

Adding a turbocharger to your engine? These are your cheapest engine management options...

By Michael Knowling

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At a glance...

  • First of two-part series
  • Cost-effective approaches to engine management when adding a turbo
  • Everything from rising rate fuel pressure regs to MAP sensor bleed valves
  • Industry experts
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Engine management is often the biggest stumbling block when adding a turbocharger to a naturally aspirated engine. You can bung on an extra injector, fit an interceptor, fiddle the fuel system and play silly buggers with the factory ECU or you can start from scratch with an aftermarket management system - but even that has its drawbacks.

Arrrgggghhh, decisions!

In this two-part series we’ll investigate different ways to tackle the engine management to ensure your engine runs happily with a ‘charger bolted on the side. In the first part, we’ll focus on no/low cost approaches...

Budget Approaches to Engine Management

Many experts poo-poo the idea of running a newly turbocharged engine without major engine management changes. But truth is, if the engine is not running lean or detonating there’s absolutely no reason why it should fail (ignoring weaknesses in conrods, crankshafts, etc).

No Changes?

In some instances, you may be lucky enough to own an engine that’ll accept forced induction without the necessity for engine management mods. If you’re not chasing a whole lot of power and you’re thinking of less than around 0.5 Bar (7 psi) boost, you may get away using an untouched management system.

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According to Lachlan Riddel, head of Gold Coast’s ChipTorque, some Honda engines are equipped with a MAP sensor that’s rated to above atmospheric pressure – around 1.5 Bar (22 psi) absolute. This means the engine management system will recognise boost pressure and Mr Riddel says it’s likely the ECU has the fuel and ignition mapping to cope with up to around 0.5 Bar (7 psi) boost. However, be aware that the MAP sensors in other vehicles will not continue to have a proportional output with any boost pressure.

In vehicles using airflow meters (rather than MAP sensors) you’ll often find there’s headroom for a few psi of boost. This is because the airflow meter will see the added turbocharger as merely a breathing enhancement (similar to an upgrade exhaust or cam swap) and, within limits, it can’t recognize that boost pressure is occurring. It’s for this reason that when adding a turbo, you’re more likely to have success using a standard airflow metered system than one using a MAP sensor.

Inevitably, the standard management will encounter some type of cut or limp-home mode when the limit of ECU maps is met. Note that this can occur at any point in the rev range – it isn’t necessarily max power that you need to be concerned about. In fact, Mr Riddel claims some management systems – such as Holden V6 systems – may enter a limp mode under deceleration. Unfortunately, there’s no way of determining how the management system will cope until you try it.

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“The success of running a turbocharger with standard management also depends a lot on the knock sensor and the ECU’s learning,” Mr Riddel says. This is crucially important in avoiding detonation. As you’ll discover, the correct ignition timing is extremely important in achieving a reliable turbocharged engine.

In addition to these management issues, the vehicle’s injectors and fuel system must have enough capacity to maintain suitable mixtures at increased output. Where boost pressure is kept low, you are more likely to avoid fuel system problems but if the engine starts to run lean, there are several low-cost approaches to increase fuel flow. (These will be discussed later.)

So, in short, you may be able to get by running a newly turbocharged engine with standard management - but this depends on the characteristics of the load sensor, the extent of ECU mapping and how much extra performance you’re chasing. You really need to ‘suck it and see’.

Keep boost pressure to minimum and you’re in with a chance.

Avoiding Cuts and Limp Home Modes

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According to the proprietor of Sydney’s Silverwater Automotive Services, David Alexander, most turbocharger fitments that run more than around 0.5 Bar (7 psi) of boost will overshoot the standard ECU tables.

“They [the ECUs] generally have only a small amount of scope above standard,” he says.

When the management reaches the limit of its mapping, or where the standard management system won’t accept any boost, there are a few alternatives...

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If you hope to keep the standard management system but you’re encountering a cut or limp-home mode that occurs on boost, it is possible to skirt around it with some simple changes. For example, this Suzuki Baleno engine hit a cut whenever the standard MAP sensor received any more than 0.35 Bar (5 psi) boost - the solution was to install a one-way bleed valve to relieve some pressure from the sensor. This eliminates the cut but results in fuel and ignition that correspond with a slightly lighter load.

In the case of engines using an airflow meter, a similar result can be achieved by installing a bigger airflow meter or a relatively small bypass passage to the existing airflow meter. Again, the ECU will be fooled into thinking there’s less load than actual – this will help avoid any cut but, because the ECU thinks the engine is running relatively light load, it’ll be more difficult to obtain ideal fuel mixtures and ignition timing.

Ignition Timing Control

“In most turbo fitments I find it’s a good idea remap the ignition timing, especially in the area where the turbo starts to come on boost,” Mr Riddel says. This achieves a smoother power curve and reduces the chance of detonation.

Interestingly, the correct ignition timing is often more important than running rich mixtures according to Simon Gischus of Nizpro Turbocharging.

“I know that everyone learns that running an engine lean will put holes in pistons but, really, it’s spark that f%&^s engines,” Mr Gischus says.

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“We’ve run modified Ford XR6 Turbo engines on the dyno at full noise for two minutes running 15:1 air-fuel ratio with no worries. People just can’t get their head around it. It doesn’t matter how much petrol you put in an engine – the advance curve must be right before anything else.”

The task of retarding ignition timing can be tackled in a number of ways.

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The cheapest approach is to turn the distributor (where fitted) a few degrees. This will retard ignition timing across the rev range – great for avoiding detonation but far from ideal for extracting maximum performance and drivability.

A better but relatively unpopular approach that’s relevant to single coil ignition systems is to use an aftermarket boost retard unit. MSD currently sell a Universal Boost Timing Master which allows you to retard timing 1 to 3 degrees for each pound of boost. A maximum of 20 degrees retard is possible. Australian company, Jacobs, also used to sell a similar product - these can occasionally be found second-hand at bargain prices.

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A much more flexible approach is to install an interceptor. Second-hand A’PEXi ITC (Ignition Timing Control) units are available quite cheaply and give +/- timing adjustment in several preset rpm zones. This is a relatively crude system that will probably get the job done but a more sophisticated interceptor – one that can be programmed on the basis of rpm and engine load – is preferable. The Xede, UniChip and Haltech units are the most popular interceptors in Australia and are well suited to tailoring the ignition curve. Of course, these units also provide programmable fuelling (important for tuning out flat-spots), load signal clamping and a host of other useful functions. Second-hand examples can be picked up from around AUD$400.

If expense is no concern you can look at the option of custom remapping the factory ECU or a programmable aftermarket ECU. We’ll discuss these in the second part of the series.

Fuel System

If you’re chasing a modest power gain, there’s a chance the standard fuel system will suffice. However, in many instances, you’ll need to do something to increase fuel flow.

If you find that the injectors are running virtually flat-out at maximum power and the mixtures are dangerously lean, the simplest way of enhancing fuel delivery is to bump up fuel pressure. This is often seen as a quick fix but keep in mind that’s exactly what Ford Australia did when adding a turbocharger to their 4-litre six...

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The easiest approach is to restrict the fuel return line to the tank (in cars fitted with a return-type fuel system). This can be achieved by plumbing a 12V solenoid and adjustable ball valve in parallel between the pressure regulator and fuel tank. When the solenoid closes at a predetermined engine load, fuel is forced to flow through the ball valve. The adjusted position of the ball valve determines the amount of extra fuel pressure you achieve. For more on this technique, see Electronic Fuel Pressure Increase

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A similar outcome can be achieved using a different - or additional - fuel pressure regulator. Several manufacturers offer rising rate fuel pressure regulators that increase fuel pressure exponentially as boost pressure increases. Rising rate regulators are fed a manifold pressure signal and, when on boost, the regulator diaphragm is compressed and fuel pressure increases. A rising rate fuel pressure regulator is quite a popular approach but some tuners, such as Mr Riddel, aren’t fans. This is because they tend to flood the engine with fuel at the rpm where full boost is achieved (typically in the mid-range).

“Certainly, rising rate fuel pressure regulators have a purpose but, to me, the way they work is more suited to something like a centrifugal blower where boost is progressive,” Mr Riddel says.

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Mr Alexander from Silverwater Automotive Services has a similar opinion.

“A rising rate reg is not a great approach from a tuner’s point of view. With a rising rate regulator, the engine usually drowns in fuel because fuel pressure is raised exponentially and the ignition timing is usually left as it is,” he says.

"Then, with higher rail pressure, you also receive lower pump flow - you’ll often need to upgrade the fuel pump to cope.”

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You may also need to increase fuel system flow.

The easiest way to enhance fuel pump flow is to increase its supply voltage. There are several aftermarket units on the market that boost pump voltage while the engine is on boost. We haven’t seen any test results of these products, but it appears they achieve a considerable increase in fuel flow. The MSD Fuel Pump Booster is adjustable up to 22V. Interestingly, we’ve also heard that re-wiring the factory pump with heavy gauge cable can maximize voltage at the pump and slightly enhance output - certainly worth investigating.

Other approaches include fitting bigger injectors and/or upgrading the fuel pump. We’ll cover these in Part Two.

Extra Injectors?

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A once-popular way to increase fuelling was to fit an extra injector (as seen in the inside bend of this induction elbow). The extra injector was typically mounted in the induction plumbing a short distance before the throttle – the injector was activated at high load and the extra fuel passed through the throttle, into the intake manifold and inside the cylinders.

Unfortunately, this approach delivered unknown cylinder to cylinder fuel distribution – some cylinders might have run rich while others ran lean. And, more often than not, extra injectors were triggered purely on the basis of boost pressure – this was guaranteed to provide over-fuelling when max boost was reached in the mid-range and relatively lean mixtures toward the top-end.

Not surprisingly, extra injectors have gone the way of the dinosaurs. Today, their only application is where extra fuel is required and there’s a beneficial cooling and rotor sealing effect inside positive displacement type superchargers (where the extra injector is mounted ahead of the blower).

Anti-Detonation Strategies

In addition to taking care of fuel and ignition control, there are some other steps to ensure happy turbo operation.

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One of the most important additions is an intercooler. This is essential to help avoid detonation (especially if you’re turbocharging with a standard management system) while also improving performance. Similarly, a water injection system can be added. Water injection is a highly effective anti-detonant and you may find slightly improved performance when using a well designed system.

Other modifications to reduce the chance of detonation include switching to colder spark plugs and ensuring the fuel tank is always filled with the highest available octane. It’s a good idea to carry a bottle of octane booster for those occasions where you can’t find high-grade fuel.

So these are the most cost-effective ways to take care of engine management when adding a turbocharger. In the next part of this series we investigate spare-no-expense approaches – are they really worth the extra?


+61 7 5596 4204

+61 3 9761 1522

Silverwater Automotive Services
02 9748 1300

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