Rick's Free Auto Repair Advice

Add a turbo

Can I add a turbo to your normally aspirated (N/A) engine?

The simple answer is yes, you can add a turbo to your normally aspirated engine. But the real answer is that to do it right, its going to cost a lot more than you think. Adding a turbo to an N/A engine it’s far more complicated than just connecting the plumbing and bolting on the turbo. If your engine has a high compression ratio like 10:1, you’ll wind up with shrapnel as soon as you add a turbo. Also, if your engine is equipped with gasoline direct injection, you’re going to have problems. The same holds true if your engine has variable valve timing (VVT).

What a turbo does

A turbo forces more air into each cylinder to increase volumetric efficiency

An engine is an air pump and every time the pistons Mahle turbodraw in air, they’re pulling (sucking actually) against a partially closed throttle plate (unless you have your pedal to the floor). That throttle plate restriction limits the amount of air each piston can draw in, and that’s what limits a normally aspirated engine to about 60% volumetric efficiency. In other words, an N/A engine normally only uses 60% of its displacement volume. The 40% loss in efficiency is referred to as “pumping loss. “

A turbo overcomes pumping loss by forcing more air (boost) into the cylinder to increase volumetric efficiency. In fact, by boosting the amount into each cylinder and doing so at a higher pressure, a turbo setup can raise volumetric efficiency up to 150% in some cases. However, the average is around 110%.

A turbo increases the final compression ratio of the engine

Even though you haven’t changed the length of the piston rod, by pressuring the cylinder, you’ve effectively increased the engine’s compression ratio and that’s where you start to run into complications.

Complications from increasing the compression ratio

Turbo air compression creates heat and heat causes knock

Any time you compress a gas, you create heat— it’s a law of physics. If you don’t cool the compressed air before it enters the cylinder, that heat can cause premature ignition or knock. Prolonged knock can destroy the engine.

A charge-air cooler (intercooler) reduces compressed air temperature


Charge-air cooler (intercooler)

Add an intercooler and route the compressed air into the intercooler before routing it to the throttle body. Create an airstream into the intercooler to cool the hot compressed air.

Switching to premium fuel reduces knock

Premium fuel (high octane) resists knocking better than regular fuel.

Lower boost pressure can overcome knock

Rather than shoot for maximum boost and 150% volumetric efficiency, you may have to limit boost to just 110% volumetric efficiency.

Water injection systems reduce knock

Injecting water into the compressed air stream can cool the air and reduce knock.

Engine mods can reduce knock

Reduce engine compression ratio by: re-boring the engine, change piston stroke by using shorter rods, use a thicker head gasket, install stronger forged low compression pistons,.

Engine mods to increase performance

• Increase port size and polish, fit with larger valves and larger exhaust headers to handle increased airflow.

• Larger air intake: Larger filter box and filter, larger air duct and larger throttle body.

• New fuel injectors and fuel pump to handle more fuel

• Computer remap.

Other engine mods to protect the turbo from failure

Add an oil cooler.

Turbos can spin at speeds up to 300,000 rpms.

turbo oil cooler

Typical turbo oil cooler

So clean cool oil flow is critical to long turbo life. A turbo cooler uses engine coolant to cool the oil down to around 200° F. Adding an oil cooler involves running an oil line to the turbo right after the oil has left the oil filter. The oil runs through the oil cooler and into the turbo, returning to the sump to be filtered and cooled again.v

Can your existing pistons, crank, cam and valves handle the extra boost pressures?

The extra power you get from a turbo causes a more violent combustion process in your combustion chambers. Your car’s pistons, valves, and other internal components may not be able to handle it. According to TorqueCars.com, “It’s not uncommon for tuners to fit larger valves, increase port size, and stronger, more expensive pistons to compensate for the boost.” If you don’t plan ahead for the increased engine stress, you may find out too late that adding a turbo wasn’t such a good idea.

airflow in turbo engine

How much does it cost to add a turbo?

A turbo kit for your specific engine should include the turbo, oil cooler, all the intake and exhaust plumbing modifications, a charge-air cooler and hoses, new fuel injectors, a remapped ECM and a new fuel pump. You’re looking at a starting point of around $6,000. If the kit you’re considering costs less than that, you’re going to have problems.

Posted on by Rick Muscoplat


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