Mitsubishi Pajero NA - NE 4G54 SOHC 8v

Dummies Guide to Vehicle Modifications!

The Mitsubishi Pajero with the 4G54 engine was released during 1982 to 1991. Available in a short and long wheel base model, this was an excellent four wheel drive vehicle.

Not too heavy compared to other larger brands, it could tow quite easily for medium loads and was still small enough to drive around local streets with ease.

The 4G54 engine with its 2.6 litre capacity, was a very strong low to mid range rpm in torque. Running a single two Venturi down draft carburetor, the engine produced

  • 85 kW (114 hp) at 5000 rpm (91 RON)
  • 198 nm (146 lb-ft) at 3000 rpm (91 RON)
  • Compression ratio: 8.8:1

Unfortunately this engine has its problems. Running a complicated balance shaft set-up, there were issues with oil pumps and timing chain issues. The factory carburettor was renowned for having choke issues, and bad fuel economy.

This modification guide is limited to engine performance modifications, being an updated version of what we use to offer on our original RPW Website back in the late 1990’s.

RPW does not take any responsibility for people performing these modifications on there car without professional involvement. Check with your local government regulations before modifying your car as these items may not be legal in your country.

Engine Performance Modifications

The following modifications are ones we have been supplying and fitting to Mitsubishi Pajero owners for over 20 years. They are proven and reliable with significant improvements in power, torque and fuel economy.

1. Air Filters & Cold Air Induction Kits

The factory air cleaner system on these vehicles, is quite restrictive.

  1. Fitting a K&N Factory Replacement Air Filter for those wanting the Stock look, with improved air flow and throttle response.
  2. Fitting a Pajero Diesel bonnet scoop to feed cold air into the engine bay. This dramatically improve the performance of any setup instead of sucking hot air from the engine bay.
  3. Fitting a snorkel system feeding into the stock air cleaner housing, already fitted with a K&N replacement filter.

2. Exhaust System Upgrade

At this point you must reach your first major decision on where you wish to go with the vehicle – in summary we recommend the following options

  1. Naturally Aspirated – replacing the stock system with a 2 1/2″ mandrel bent system from the factory manifolds back produces great improvements.
  2. Turbo Charged – low boost system under 10 psi – a 2 1/2″ mandrel bent system is more than adequate, but would keep noise levels at a lower levels
  3. Turbo Charged – boost systems 10 psi or higher – a 3″ system would be required for the horsepower levels this engine would be creating. With a good oval shaped muffler, resonator and cat converter would provide a good balance of sound and performance.

These can produce small gains with the basic systems of around 5 – 10kw at the wheels, with improved fuel economy and torque.

3. Extractor Upgrade

If your plan is to go turbo, then save your money and jump ahead several more levels. This is not for you. For everyone else, this will complete the balance of your exhaust system modifications. The factory manifolds are like most systems, restrictive. FittingĀ  of these will have dramatic results in torque and power. There are various designs, being either 4-2-1 or 4-1 designs.

The 4-1 designs are more performance orientated for the heavy four wheel drive users, the 4-2-1 designs more for the every day driver with limited modifications planned.

This package adds around 5kw at the flywheel with increased torque and improved upper acceleration and rpm range.

3. Carburettor Upgrade.

The stock system on this vehicle, as already stated is terrible for both fuel economy and issues with the chokes jamming on, throttle response and overall performance. RPW has for many years been supplying for many years a carburettor and intake manifold package which rectifies all these issues. Contrary to popular opinion, a 2 barrel Holley Carby is not the way to go. The Holley 350 units are simply too simple and too large for these vehicles.

We recommend instead using two options of carburettor

  • Weber DGAV 32/36 unit for the majority of applications
  • Weber ADM34 unit for more high performance applications.

This unit upgraded with a ported, machined inlet manifold and K&N Air cleaner set-up will produce gains of over 20 – 30hp at the wheels with dramatic improvements in acceleration and fuel economy when tuned properly. The ADM34 is our preferred unit with its electronic shut-off for fuel on the idle circuit, but it does cost more to fit this unit.

Webber’s are our preferred choice due to there advanced tuning options of idle jets, main jets, emulsion tubes, air bleeds and accelerator pumps. This is the only option for those wanting to go further with the vehicle, short of a fuel injection upgrade instead.

4. EFI Conversion

For those wanting to do a turbo conversion later, or wanting the maximum power and fuel economy for naturally aspirated application, an Electronic Fuel Injection conversion is the next best option.

This is done by adapting a Mitsubishi Magna TP inlet manifold, modifying the plenum chamber and remounting the throttle body on the other side. Various water lines will need to be modified but that is fairly easy to do. You will also need the TP Magna distributor to provide the appropriate crank and camshaft trigger signals.

To do this conversion you will also need to do a fuel pump upgrade. The best method of this is to hook up a primary low pressure fuel pump to a surge tank. From there a high pressure external pump feeding fuel up to the fuel rail, followed by a return line back to the fuel tank.

The final piece needed will be an after market ECU system to tune and run the vehicle. This will be needed to control the fuel, idle speed and thermo fans, air conditioning etc.

Gains would be in the realms of 10 – 15kw on a naturally aspirated vehicle, with fuel economy and torque being the largest improvements.

6. Camshaft Upgrade / Cylinder Head

We assume at this stage that you have done everything above. From there camshafts are the next logical choice. There are always the options for a stage 1 improved profile for those wanting something small for general improvements across te board.

The factory set-up on the Pajeros, in the early NA – NC models run adjustable tappets. The later model ND – NE models run hydraulic rocker arms.

The ultimate package we recommend is to do a upgrade to Roller Rocker Hydraulic rocker arms from the TR – TS 4G54 Pajero. This in conjunction with a billet roller rocker camshaft provides the best overall gains of horsepower, torque and efficiency.

RPW has for a long time, recommended the use of a particular profile camshaft. This has been derived from the Paris – Dackar racing where Mitsubishi Pajeros dominated for many many years. This camshaft has been proven to provide improved low rpm torque, but additionally, improved working rpm range. Peak torque is produced 500 rpm earlier than the stock camshaft set-up. This camshaft requires valve springs to be changed and fitment of a vernier camshaft gear is also beneficial.

7. Engine Internal Upgrade

Modifications to the engine are the final step. The recommended package is to at the least, rebuild the engine with the above camshaft upgrades, with increased compression of at least 9.5 : 1, or as high as 10.5 : 1 if possible (With EFI Conversion).

The normal package we provide to our customers is a rebuilt engine with 10.5 : 1 pistons, increased bore and stroke out to 2.9 litre, with the camshaft and weber package. This usually produces around 100 – 120hp at the wheels compared to the bog stock factory 50hp at the wheels. Torque is nearly doubled in comparison and the frequent comments we get from customers, is that the vehicle on the road, essentially has an extra gear when driving. Rather than needing to drop a gear to overtake, they can stay in the higher gear and simply accelerate with this package.

8. Turbocharger Conversion Package

What more can we say other than your a horsepower and boost Junkie. Welcome to the rest of the world. This combines extreme levels of torque and power, with neck snapping acceleration. It comes at a cost though, increased fuel economy, higher insurance and lots of money. But lets get something clear first.

Do the job properly and although it may cost more, it will last longer, provide trouble free maintenance and be everything you want it to be.

  1. For boost levels up to 10 psi can be done safely on the stock head gasket dependent upon tuning and inter-cooler efficiency. This can be done on a stock internals without any issues.
  2. For boost levels over 10 psi would require engine internals to be strengthened with forged pistons and conrods.

The 4G54 engine at around 10 psi is good for around 140kw at the flywheel. With a worked engine, 200+KW are easily achievable.

Did you like our guide? Something did not make sense. Please let us know and we will try to update this with more relevant information etc. We hope this helps you plan your vehicle modifications in a more informed manner.