Tuning the Hyundai Theta

"Comprehensive guide to modifying and tuning the tuning and performance parts on the Hyundai Theta engine!"

TorqueCars will review Theta tuning and provide tips on the ultimate upgrades. Hyundai Theta are popular tuning projects and with the optimum tuning mods like remaps, turbo upgrades and camshafts you will greatly maximise your driving fun.

When talking about the top|ultimate|best|greatest|best|optimum parts for your Theta engine, we are going to concentrate on the mods that give the best power gain for you money.

Significant gains on the Theta can be made from camshaft upgrades. Altering the camshaft profile alters the intake and exhaust durations on the engine and can dramatically change the power band and power output.

NB: Fast road camshafts tend to boost the bhp and torque throughout the rpm range, you may lose a little low end power but higher rpm power will be better.

Motorsport and race camshafts, boost the higher rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Race cam is not great driving around busy urban areas.

You should ideally optimize your bhp range to your usage of the car so for a road car stick with a shorter duration Theta cam

Each engine responds better to different camshaft durations check your engine on a rolling road.

The ecu map and fuelling also will make differences on the power gains you'll get.

A longer valve duration can alter the power band and on most engines the exhaust and intake durations do not need to match, although most cams and tuners use matched pairs there are some advantages to extending the intake or exhaust durations.

Stage 1 mods: Sports exhaust manifold, Fast road camshaft, Intake headers, Remaps/piggy back ECU, Panel air filters, Drilled & smoothed airbox.

Stage 2 mods: induction kit, Sports catalyst & performance exhaust, high flow fuel injectors, fuel pump upgrades, Fast road cam, Ported and polished head.

Stage 3 mods: Twin charging conversions, Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Crank and Piston upgrades to alter compression, Engine balancing & blueprinting, Internal engine upgrades (head flowing porting/bigger valves).

Review your options and then acquire your tuning parts and set yourself a power target to avoid costly mistakes.

remap will help release the full potential of all the parts you've done to your Theta.

It will usually give around 30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but the outcome often rely on the parts you've carried out and the condition of your engine.

It is the main goal to any car tuning job to pull air into each cylinder

Intake carry the air during the suck phase from the filter and allow it to be pulled into the engine cylinders.

The size of bore and shape and flow characteristics of the Plenum can make a big effect on to fuel atomisation and engine efficiency on the Theta.

Commonly we find the intake manifold are crying out for motorsport parts, although a few car makers provide reasonably good intake manifold.

Larger Theta valves, getting port matching and head flowing will also increase power, & more importantly will permit a better power increase on other mods.

Turbo upgrades

NASP engines need quite a lot of work when you add a turbo, so we have a separate guide to help you take into account the pros and cons of going this route on your Theta

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes superb power gains.

When a car is fitted with a turbo mods are relatively easy and turbo engines are built using uprated components.

There are weak spots for every engine, with some being incredibly solid and some only just able to handle stock power

Discover these restrictions and install forged components to cope with the power.

It's not unheard of drivers spending a loads on turbocharger upgrades on the Theta only to see the motor go up in smoke on it's first outing after it's used in anger.

Bigger turbochargers tend to experience low end lag, and little turbochargers spool up really quickly but do not have the high rpm engines power gains.

Thanks to new tech the choice of turbochargers is always increasing and we are seeing variable vane turbochargers, allowing the vane angle is altered according to speed to lower lag and increase top end performance.

Twin scroll turbochargers divert the exhaust gases into two channels and direct these at differently angled vanes in the turbo. They also boost the scavenging effect of the engine.

You'll commonly see there is a limitation in the air flow sensor AFM/MAP on the Theta when loads more air is being fed into the engine.

We note 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped torque at a much lower level.

Adding a supercharger or additional turbo will make large power gains, although more complex to setup. We have this in depth look at twinchargers if you want to read more.

Fuelling upgrades and mods

Don't dismiss the need look at the fuel delivery when you are increasing the performance - it makes the car more thirsty. We strongly recommend you to be generous with your injectors flow rate.

The rule of thumb is to add 20% when fitting an injector, helps cope with injector deterioration and allows a bit of spare capacity should the engine need more fuel.

We think this one is common sense, but you'll need to match your fuel injector to the type of fuel your car uses as well.

Exhaust upgrades and mods

You should look to improve your exhaust if your current exhaust is actually causing a restriction in flow.

On most factory exhausts you'll find the flow rate is still good even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Sports exhausts can usually air flow through the engine but do not go too big or you may end up will reduce the flow rate. Stick to 1.5 to 2.5 inches as a rule of thumb.

Typically exhaust restrictions are in the catalyst installed, so adding a faster flowing race alternative will help avoid this restriction.

Weak spots, Issues & common problem areas on the Theta

The engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the , particularly when the engine has been modified and is putting down more power than the manufacturer intended.

There was a recall back in 2014 on both the 2.0 and 2.4 liter engines due to a fault in the crankshaft manufacture where metal shards would restrict oil flow and caused premature wear on the bearings. The issue would initially manifest itself as a grinding noise/vibration.

History of the Engine

  • 2.0L (G4KA) 143 hp (140 lbft
  • 2.4L (G4KC) 162 hp 164 lbft

Theta II

  • 2.0L (G4KD) 163 hp 146 lbft
  • 2.4L (G4KE) 176 hp 168 lbft

There were a few turbo variants of the Theta II

  • 2.0L MPI turbo 223 hp  223 lbft
  • 2.0L GDI turbo 274 hp 269 lbft
  • 2.0L GDI turbo 271 hp  260 lbft
  • 2.0L GDI turbo 255 hp 260 lbft

The Theta engine found it's way into the following models.

Theta/Theta-II (2.0L)

2.0L DOHC engine in a Kia (G4KD)
(G4KA, G4KD)

  • Hyundai ix35 (2010-present)
  • Hyundai Sonata (2011–2014)
  • Kia Forte (2009-2013)
  • Kia Rondo (2007-present)

Theta/Theta-II (2.4L)

(G4KC, G4KE, G4KG, G4KJ)

  • Hyundai Santa Fe (2010-present)
  • Hyundai Sonata (2006–2010)
  • Hyundai Sonata GDI (2011-present)
  • Hyundai Sonata (2011-2019) (Middle East)
  • Hyundai Starex (2007-present)
  • Hyundai Tucson (2010-present)
  • Kia Cadenza GDI (2011-present)
  • Kia Forte (2010-2013)
  • Kia Optima (2006–2010)
  • Kia Optima GDI (2011-present)
  • Kia Rondo (2007-present)
  • Kia Sportage (2011-present)
  • Kia Sorento (2011-present)


Theta-II 2.0 Turbo (2.0T)

2011 Hyundai Sonata Limited 2.0T, turbo GDI engine
(G4KF, G4KH, G4KL)

  • Genesis G70 GDI (2019-present)
  • Hyundai Genesis Coupe (2009-2014)
  • Hyundai i30N GDI (2019-present)
  • Hyundai Santa Fe (Sport) GDI (2013-present)
  • Hyundai Sonata GDI (2011–2014)
  • Hyundai Veloster N GDI (2019–present)
  • Kia Optima GDI (2011-present)
  • Kia Sorento GDI (2016-present)
  • Kia Sportage GDI (2011-present)
  • Kia Stinger GDI (2018-present)

For more information on Tuning your engine please join us in our friendly forum where you can discuss tuning options in more detail with our owners. It would also be worth reading our unbiased tuning articles to get a full grasp of the benefits and drawbacks of each modification.

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