Adding an aftermarket turbo to a car.

"You can't just 'bolt on' a turbo, it takes careful planning"

In this article we are going to discuss an often raised topic, that of adding a turbo to a naturally aspirated (NA or NASP) engine.

The idea of doubling your NASP (NAturally ASpirated) engines power with one "simple turbo upgrade" is certainly appealing, but what is involved in a turbo conversion project? What are the common problems when a car is turbocharged? How do you add a turbo safely to a car?

Forced induction is where highly compressed air is fed into the engine. We would typically use a Supercharger or Turbo to do this.

More air means you can burn more fuel, and by forcing in this compressed air you theoretically increase the cars ability to burn fuel.

Contrary to popular belief this is certainly not a straightforward bolt on part. As you will discover from this article there are lots of additional things needed to make it work.

Adding a turbo or supercharger is a fairly complex modification and one which regularly comes up in our forums so we'll cover the basics of adding a turbo upgrade in this article.

Please watch our video feature on adding a turbo to your car

Modern technology uses ceramic bearings and variable turbine geometry to maximize power and torque.

turbo-civic

Why add forced induction?

The basic reason for forced induction (turbo or supercharger) is not to increase the engine's compression or the maximum pressure in each cylinder.

Actually, the primary reason is increasing the engine's volumetric efficiency (the efficiency of the engine at drawing in air and converting this to power by adding fuel and burning it).

In video games like GranTurismo and Forza, we just tick a box, and within seconds our car is fully turbocharged and running much faster. In the real world, things are very different.

Put a turbo on an engine with an 10:1 compression ratio and watch it explode! (Unless you have direct injection or anti knock protection) We list the additional mods required when adding a turbo to a NASP engine.

What does the turbo do?

The turbo spins faster as the exhaust gases flow faster, compressing more air.

Due to the high temperatures and speeds of a turbo, oil supply is critical. According to our testing at TorqueCars, ball bearings outperform thrust bearings and are the preferred choice for turbo upgrades.

Put a turbo on an engine with an 10:1 compression ratio and watch it explode!

Higher compression engines use direct injection (where fuel is fed into the cylinder at the last moment) as this helps to avoid premature ignition issues, and has been effectively used on modern petrol engines, something they borrowed from diesels.

You could also use water injection to dampen the intake charge and retard the timing, but you are starting to get into rocket science territory here, and if you don't know what you are doing I guarantee you will run into problems.

Please watch our video which explains turbos and all you need to know about them. Be sure to subscribe and support our new channel.

There are a lot of considerations to make when adding a turbo to a NASP engine.

But to improve this the air needs to be forced into the engine, hence the popularity of turbocharger conversions.

So let's look at what's involved in this mod and pass on some of the tips we've picked up along the way so you don't end up making the common mistakes.

How to install a Turbo on a NASP engine.

Things to take into account when adding a turbo to a non turbo car (NASP or naturally aspirated engine).

  1. Choose an appropriate turbo, generally, you are better off with a low boost turbo that can spool up quickly.
  2. Make sure you have enough fuel, this will mean upgrading injectors and the fuel pump
  3. Get an Intercooler, this will be needed to take the intake temps back down after the turbo FMIC's are best
  4. The exhaust manifold and intake piping will need to be revised, a good kit will be designed to bolt on and should have all of the components you need
  5. Lowering the engine's compression ratio is usually required although some cars will allow a modest level of boost on stock internals, detonation is your big enemy here.
  6. Mapping  is essential if this is not done you risk serious damage, in some cases, an aftermarket ECU is better than trying to modify your current ECU map. Ideally, this should be done on a rolling road.
  7. The turbo will need a supply of fresh oil and the manufacturer's recommended grade may not be sufficient for your turbocharged engine.
  8. Make sure the engine is strong enough, forged crankshaft, conrods, and pistons are a good idea but the quality and suitability will vary according to your needs. (This is a good way to lower the compression ratio.)

If you are thinking of adding a turbo to your car we suggest you join our friendly forum and get some specific tips and advice for your car model.

The Intercooler

What is an intercooler and what does it do?

An intercooler is effectively a radiator which allows the intake air charge to be cooled before it gets into the engine.

You would ideally mount an intercooler in front of the radiator so that it benefits from all that nice cold air hitting it.

Top mounted intercooler

It would be plumbed in after the air intake filter and after the turbo or supercharger where most of the heat is added.

Most cars have front mounted intercoolers which sit in front of the radiator and as a result they tend to offer superior air cooling over top mounted intercoolers.

You need to take into account the fact that the air reaching the radiator is reduced so you may in extreme cases need to uprate your cars radiator to maintain low on track temperatures.

Power benefits from an intercooler

One of the mods that eliminates a restriction is the addition of an intercooler. It aims to improve the engine's capacity to draw in air effectively and maintain a high level of cooling for extended periods of time.

5 to 10 percent greater power and longer heat soak resistance may be gained with an intercooler layout that is well-designed.

The advantages of installing an intercooler on your vehicle are explained in a video we've put together. Subscribe to our new YouTube channel and show your support for us.

Front mounted or top mounted?

Top mounted intercoolers

  • Top-mounted intercoolers provide the advantage of a shorter, lighter route from the compressor to the engine.
  • As hot air rises from the engine compartment, there will be less cooling, resulting in faster warming.

Front mounted intercoolers

  • It's easy to install since most OEM intercoolers are located on either the front or side of the engine compartment, and it provides the optimum cooling because it faces the air entering the engine.
  • Inconvenience of a longer intake hose from compressor to engine; heavier vehicle.

Some cars are equipped with top-mounted intercoolers that draw air in via the bonnet, which may cause the car to be subjected to warm air from the engine compartment when it is stationary.

Because the air is warmer, you can burn less gasoline, which is better for your wallet because you don't want to be running big power levels while stuck in traffic.

As an example of a vehicle with an intercooler installed on top, consider the Subaru Impreza. A top-mounted intercooler provides a far shorter air flow path into the engine, but it will need an air scoop on the top to channel air through it, which might result in drag.

All turbocharged vehicles will benefit from an intercooler, and OEM intercoolers may be improved upon. Your engine needs as much air as possible sucked in via the intercooler core, therefore if it is obstructed, you will lose power.

Those who say that all intercoolers reduce airflow are wrong; the advantages of installing a high-quality one outweigh the little loss of airflow that comes with a well-designed intercooler.

Each 100 horsepower requires 3 litres of intercooler capacity, on the average. It's a crude rule of thumb, but it appears to work for most vehicles with 150-400bhp!

When it comes to intercoolers, selecting the right size for the application is critical since a huge intercooler might impede airflow (this is something which can be discussed in more detail in our forum.) It's not always preferable to go bigger!

Why fit a turbocharger?

When a naturally aspirated engine sucks air in, it can only draw so much in before the intake valve closes and seals the cylinder.

The average Naturally Aspirated  "NASP" engine will only pull in around 60% of its potential volume, so as a result is only 60% volumetrically efficient.

This is why we don't often see NASP cars producing more than 100bhp per liter - props go to Honda for reaching this level though, but we'll discuss that in another article.

turbo-intake

The more highly tuned an engine is, the more efficient it will be.

A typical TorqueCars member will have already spent much time and effort tuning their NASP engines but will still struggle to get anything approaching 85% efficiency when using Natural Aspiration.

The best way to increase power is to force more air and correspondingly more fuel into the cylinders (forced induction) thus filling them more.

The average forced induction engine runs from 110% to 150% volumetric efficiency (the incoming air is compressed).

Here are some examples of this to help provide context on the benefits of adding a turbo. A 2 liter NASP motor will use effectively around 1200-1300cc of its capacity and will typically produce up to an optimum 200bhp (based on 100bhp per 1000cc).

A turbocharged or supercharged 2.0 liter engine will use much more of it's capacity, producing more power as it is now able to burn more fuel. (This gives a turbo engine an optimum power figure far in excess of 100bhp per cylinder, some OEM 2.0 engines are pushing out 300bhp!)

Take an extreme example of a turbocharged 1.6 engine in early Formula 1 motorsport that produces almost 1500 bhp.

We frequently see tuned 2.0 litre turbo cars hitting 600bhp and more with relative ease providing daily use whilst maintaining reliability. The key is in having a strong block and components to work from.

  • The more boost you run, the more efficient the engine, hence we have 1.4 litre turbo engines producing as much power as large V6's.
  • Having a small but powerful engine, gives you a weight advantage too, improving handling and making the power hike even more impressive when driving the car.
  • But the main benefit from increasing boost is to increase the final compression ratio and get a better bang from an increased air/fuel charge mix in your cylinders (the actual engines compression ratio stays the same but as there is more air coming into the engine it will become more compressed).
  • If you increase the amount of air/fuel in the cylinders, then as a result you will increase the compression, which could be too much. In order to keep the final running compression the same, the initial compression (without boost) has to be dropped to compensate.
  • More air will enable more oxygen to be available for burning and with the addition of additional fuel, the engine will release more power.
  • Turbocharging is the best way to increase the efficiency of an engine.
  • When adding a turbo to an engine that was not originally designed for a turbo there are some major complications to take into account.

How a turbo works

In the illustration below the exhaust gases in RED spin the turbo which sucks in cold air shown in blue, that is mixed with fuel shown in green in this port injection engine and then the pressurized mixture is combusted in the cylinder.

We now have twin scroll turbos which split the exhaust gas flow into two channel from alternative cylinders, this aids a spool up and allows the turbo to spin faster at the top end.

The pictures below show the intenal view of a standard turbo compared to a twin scroll turbo.

In a twin scroll turbo the turbine blades are generally shaped to catch the exhaust flow effectively.

See our guides and articles on Turbos which explain the many options from hybrids and twinscroll turbos.

ECU Mapping for a turbo conversion

Making sure the fuel delivery matches the new quantities of air being pushed into the engine is a top priority, and this will also require adjustment to the spark advance.

After you've added a turbo this has moved things far beyond the expectations of your OEM ECU. So what can be done about this?

To get the greatest power out of your turbo conversion, you'd need to alter the timing and fuelling. Fuel flow and spark timing advance can now be finely tuned with an electronic ignition system.

Only in a narrow RPM range did you get near-perfect spark timing. Using a table, the ignition program was able to read the predetermined timing from a complete list of variables.

Precision control of the ignition timing is now achievable thanks to air temperature, engine speed, and load as well as the control over turbo/wastegate control and fuel delivery rates.

Control over fueling and power output can now be finely tuned with the latest Turbo chargers and injector technologies. Engine and engine technology have advanced to new heights as a result of the manufacturers' focus on emissions compliance.

Beware of power spikes - see the red line in the diagram below, the green shows a good stead power increase following a profile similar to the stock engine. Power spikes cause wheelspin and are prone to stress engine and turbocharger components.

Most turbos come with airflow maps that can be used to calculate the fuel requirements.

We have a video that explains ECU mapping in more detail.

Aftermarket ECU's

It helps you to get more out of your vehicle than the OEM ECU. Normally, stock ECUs are limited.

Instead of focusing on peak performance, automakers usually prioritize the life of various vehicle components rather than following international standards.

Everywhere you look, you'll find aftermarket ECUs for certain vehicle models and uses. They help cars operate better, pass pollution tests and save fuel. An Aftermarket ECU Is Better.

Factory-installed ECUs are built to last. The car's performance is compromised. In many cases, the OEM ECUs cannot be remapped, especially in Japan.

Because aftermarket ECUs allow interested parties to increase their vehicle's performance to new heights, they are a valuable investment.

How Does an aftermarket ECU Work?

Every ECU works on the same premise. Input sensors such as engine load, intake temperature, and RPMs are analyzed to make judgments. Also, aftermarket ECUs are programmed to perform certain functions.

The ideal setting for optimizing fuel usage and spark advance is determined by an aftermarket ECU.

The latest trend we see are manufacturers using small capacity engines with turbochargers fitted, and we see a modern 1.4 turbo putting out as much power as an early 2.0 turbo or 3.0 NASP engine, with much better fuel economy and it weighs lot less.

Problems when fitting an aftermarket turbocharger.

turbo-x-section

Pre-ignition or knock - this is where the fuel ignites under pressure before the spark happens.

This will cause a piston to move in the opposite direction if it has not reached the top dead center and will have disastrous consequences for the engine.

Avoiding preignition and detonation

To avoid detonation (premature ignition) you will need to lower the compression ratio of the engine, and/or restrict the turbo to a lower boost threshold.

(Low compression engines fitted with a turbo will also avoid some of the turbo lag problems inherent in most turbo applications.)

The best turbos to add to a non turbo NASP (Naturally aspirated) engine are small units with low boost levels. Remote turbo kits are gaining popularity thanks to the low boost they provide and not needing space in the engine bay.

Another option you have is to fit a water injection kit to dampen the air charge and prevent detonation.

To lower the compression you can go with a  re-bore and fit lower compression pistons, you can add a stroker kit to alter the compression ratio by adjusting the compression stroke length.

For minor adjustments, you could get a larger head and thicker head gasket thus increasing the combustion chamber volume thereby reducing the compression ratio.

You need to aim for around a 7:1 compression ratio if you are adding a turbo, anything above 9:1 and you will have problems. Modern direct injection engines run much higher compression ratios.

In all cases, you should use the highest octane fuel that you can find as the higher the octane the more resistant the fuel is to engine knock.

With the right fuelling though we have seen people running 25psi of boost on a 10:1 compression ratio but we should add that the aftermarket ECU and fuelling mods were of a very high specification on this application.

If you can reduce the boost pressure to 5-7psi (as opposed to 25-35psi), and use the higher octane fuels available (e.g. Shell Optimax) you should be able to run a turbo on a standard engine with around the 9:1 compression ratio. For information on Octane and its effect on engine knock read our octane article.

Direct injection as pioneered on Diesel engines is finding it's way into petrol engines and because the fuel is injected later into the intake charge it reduces the temperature of the charge helping to resist premature ignition.

This is why FSi and Di turbo engines can run very high compression ratios.

Further engine mods to aid reliability and power

When adding a turbo, for maximum performance gains, you should also get the head flowed, increase the port size, fit bigger valves and go with a larger exhaust header and system as there will be a much larger volume of air flowing through the engine.

Fitting an adjustable boost controller will allow you to experiment on a rolling road while attached to diagnostic equipment to find the optimum boost pressure and timing advance.

Particular attention should be paid to fuelling. More air requires more fuel or you risk the danger of burning too lean.

You also want to avoid over fuelling when the boost from the turbo drops as this can destroy the engine.

On most aftermarket turbo applications it is unlikely that the car's existing fuel delivery system will be able to deliver sufficient fuel so you will need to uprate the fuel pressure with a new pump and fuel pressure regulator, the injectors will also need uprating.

The car computer will also need to take into account the new fuelling requirements of a turbo, especially with regard to throttle position and wastegate control and rapidly changing fuel requirements between on and off boost conditions.

The air intake will also require upgrading, as few OEM air intakes can cope with the air requirements of a 40% power hike.

We strongly recommend a good aftermarket ECU to allow you to create a custom map for your new turbocharged engine.

Most kits contain only the necessary parts to physically get the turbo onto the engine such as an exhaust header and the necessary intake plumbing to the air filter.

Turbos are expensive but will add the most power for your money. You should allow about 40 hours for fitting, you really do need to know what you are doing and will require the ability to create a custom ECU map.

Generally speaking, though it will usually be easier to source a turbocharged engine and do an engine transplant to this than add a turbo to a NASP engine.

Most manufacturers now have a turbo charged engine in their line up which would make a suitable donor for your project.

Turbo terminology

Wastegates

A wastegate prevents excessive exhaust flow from exceeding what is required and allows control over the boost. The wastegate diverts exhaust gases away from the turbo's propeller, reducing turbo lag.

Bov's diverter valves

A blow off or diverter valve controls the intake pressure. see our BOV article

Variable geometry turbos

Some modern engines have variable geometry turbos, which allow the speed of the turbo to be changed by varying the angle of the propellers.

Twin scroll

Twin scroll turbos take alternative inputs from the cylinders in two streams rather than one, and this benefits the cars power with a faster spool up time and less lag.

Turbo Lag

This is the delay before the turbo spins fast enough to provide boost, larger turbos tend to require more effort to spin them up but they can provide higher power levels at the top end.

ECU

This is the cars computer which controls ignition, fuel, spark and in many cases the turbos wastegate and boost control.

History of Turbocharger development

Let's finish with a look at the history of the turbocharger

The turbocharger was designed by Swiss engineer Alfred Buchi, who previously worked on steam-powered turbines. He patented internal combustion turbo applications as far back as 1905.

Most aircraft-oriented applications were designed to enhance operational altitude by increasing air pressure and therefore compensating for low atmospheric pressure at high altitudes.

Fred Agabashian qualified for pole position at the Indianapolis 500 and led for 98 kilometers in a turbocharged vehicle in 1952!

The first turbocharged car was the 1962 Oldsmobile F-85 Turbo Jetfire, followed by the 1978 Mercedes-Benz 300SD.

In the 1980s, Yamaha, Kawasaki, and Suzuki added turbochargers to inline 4 engines to increase power without adding weight.

Further reading - in depth articles about turbos.

TorqueCars suggest that you join the friendly tuning forum and get some specific tips and advice for turbocharging your car model - we now have a dedicated turbo tuning forum.

Check out my YouTube channel, we're regularly adding new content...


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10 Responses to “How to add a turbo to a non turbo car.”

  1. Tyler Langlois says:

    Very notifying i also am looking to put a turbo into my 1998 ford mustang v6 3.8 liter were do i even start to build up to it

  2. jos hage says:

    i build a gt35 watercooled turbo on a toyota mr2 spider (1zzfe).
    i am running with all stock,beside the maf converter (apex)..as long i dont go over the 7 psi it is all ok.
    last dyno i had 239 hp (stock 138)so..100 ps more with 7 psi..not bad for this light car.the result is i need a extra gear (6 speed..??)

  3. TCJBOLDIE says:

    Don’t agree with lowering the CR to 7-1.
    I have a 4G63 stroker with 8.7-1 ratio with 18 psi boost780cc injectors and a Haltec computer with a forged bottom end and touch wood zero problems to date 4 years and 15000klm (track and occasional weekend drive)

  4. Julio says:

    I have nasp engine with a 10:1 ratio. How much psi would i be able to run? And what injectors should i use?
    Can i run turbo with same compression? Thanks julio

  5. TCJBOLDIE says:

    low comp turbos are more laggy off boost but can run more boost.
    My car has 8.7-1 CR and 17psi

  6. mark singh says:

    I’ve got an engine with a 9:1 cr what’s a safe boost pressure can i run on 94 octane fuel

  7. THE D KONSTANTINOU says:

    The best article for a good experience with tubo world. In general it is a challenge to fit a turbo on simple [etrol engines. Need a lot of work and much money to be safe and smooth as required.

  8. Acacio Mazive says:

    Thanks very Much for this Article I`ve learned to Much, there is no many info about Mod a N46 I have been searching for long time and nothing, this info was very helpful and I see that I can make my 118i BMW runs better without Swap the engine.

    My Question is? I want to Turbo my N46 engine, I already have a M52 Garrett turbo small one,( low boost) I wanted to fix it without changing anything in the engine but exhaust and airflow. will it create me problems.

  9. Jim says:

    Great article,
    It’s hard to out do oem now days , but people just want to be a little faster than the stock vehicle….for bragging rights. I chose a ecu “fooler” that tricks the stock ecu into raising boost but doesn’t over ride programming…It has built in safety’s for folks like me that olny know enough to be dangerous…It’s noticeably faster than stock,,but hasn’t blown anything in over 60k miles

  10. Colleen says:

    Well presented thank u

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