Hyundai Theta Tuning

"All you need to know about tuning the Hyundai Theta engine!"

We shall review and look at Theta tuning and report on the optimum modifications for your car. Hyundai Theta make a good tuning project and with carefully chosen sports upgrades like remaps, turbo upgrades and camshafts you will really maximize your driving experience.

We review and look at Theta tuning and point out the ultimate modifications. Hyundai Theta offer good returns when tuned and with the right motorsport parts and mods.

History, Power & Specs 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)

Theta/Theta-II (2.4L)

(G4KC, G4KE, G4KG, G4KJ)


Theta-II 2.0 Turbo (2.0T)

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

Best Theta modifications

The best tuning parts on an engine are in our opinion the ones that give the biggest return for your cash.

We won't be swayed by popular Theta tuning parts, they need to be cost effective.

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

Fast road camshafts normally increase the torque across the rev range, you might lose a little low down torque but your higher rpm power will be better.

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

On a road car must carefully try to match your engines power to your preferences.

I'd be completely gobsmacked if you find a Motorsport cam is a pleasure to live with when driving around busy urban areas. This is because a competition cam causes a very lumpy idle, and makes the car more prone to stall or jerk along in stop start traffic, sadly though many ignore this and end up ruining a perfectly good car and having to revert back to a fast road, or OEM cam profile.

Different Theta engines respond better to extreme cam durations than others.

The ECU mapping and fuelling also will make differences on the power gains you'll achieve.

Altering valve durations 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.

Please watch our video which covers the 5 principles of tuning your car. Be sure to keep up with our latest YouTube content and subscribe.

Best mods for your Theta

  1. Tunes - A tune/remap gives the most advantage for your investment, aftermarket ECUs, and Tuning boxes are all alternatives.
  2. Upgrades to turbochargers and superchargers - forced induction is the most dramatic method to increase your intakes air supply, allowing you to utilize more fuel and make higher power. It is one of the most expensive modifications it offers big gains.
  3. Air Induction and Performance Exhausts - Please be warned on their own these mods won't ADD POWER for most setups, but they enable you to release power after other modifications by lessening the restriction.
  4. Flowing and porting the engine head - for larger gains, you will get better flow and make a more efficient engine if you do this to support your other mods.
  5. Fast road cams are one of the most significant mechanical changes, but we strongly suggest they be installed by someone competent and you might struggle to find one but you'll probably find a local firm to regrind a stock camshaft for you.
  6. Low mass flywheel - a lower weight flywheel will significantly improve the engines free revving nature. In some cases flywheel lightening is not not a great upgrade for all Theta engines.

Theta Tuning Stages

Typical stage 1 mods often include: Panel air filters, drilled & smoothed airbox, Sports exhaust header/manifold, Intake manifolds, Remaps/piggy back ECU, Fast road camshaft.

Typical stage 2 mods often include: high flow fuel injectorsPorted and polished head, fuel pump upgrades, Fast road cam, Sports catalyst & performance exhaust, induction kit.

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

The Theta power plant respond well to upgrades and we note that there are quite a few choices of upgrades and performance parts about.

Remaps should help to establish the full potential of all the tuning mods you've fitted to your Theta.

(In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

It will usually give you around 30% more power on turbocharged vehicles and 15% on NA (naturally aspirated) engines, but you mileage will vary depending on the tuning mods you've done and the condition of your engine.

It is the main goal to any engine modification job to feed air into the Theta engine

Intake manifold flow the air during the suck phase from the air cleaner and allow it to be drawn into the engine cylinders with fuel for the squish phase.

Design and flow characteristics of the Intake manifold can make a big difference to fuel delivery on the Theta.

We often see air intake manifolds are crying out for an upgrade, although some manufacturers provide reasonably well designed air intake manifolds.

Larger Theta valves, doing some 3 or 5 angle valve jobs and porting and head flowing will also boost torque, this will make space for raising the torque increase on other upgrades.

Turbo upgrades

NA (naturally aspirated) 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 to get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes massive power gains.

If the engine is fitted with a turbo upgrades are giving better power gains and we find turbo engines use many forged and stronger components.

However engines will have power limits

See where you'll find these limits and fit better quality crank and pistons to cope with the power.

We see many people spending a loads on turbo charger upgrades on the Theta only to watch the engine block literally blow up on it's first outing after it's used in anger.

Large capacity turbo units commonly experience a bottom end lag, and smaller turbo units spool up more quickly but won't have the top end power band gains.

Thankfully the world of turbos is always increasing and we now see variable vane turbos, where the vane profile is altered according to speed to lower lag and increase top end performance.

Twin scroll turbos divert the exhaust flow into a couple of channels and flow these at differently angled vanes in the turbocharger. They also boost the scavenging effect of the engine.

You'll commonly see there is a limit in the air flow sensor MAP/MAF/AFM on these engines when considerably more air is being drawn into the engine.

You'll see that 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor limited bhp and torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp gains, although harder to configure. We have a twincharger bhp adding guide if you want to read more.


You will need to ensure that the engine is not starved of fuel so should look at the fuelling when you start going beyond 20% of a power increase.It makes sense to over specify your injector capacity.

The rule of thumb is to add another 20% when buying an injector, helps cope with injector deterioration and gives a bit of spare capacity should the engine require 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.

All the following flywheel power targets will assume an injector duty cycle of 80% and a base of 58 psi of fuel pressure at idle.

4 Cylinder turbocharged engines

  • 58 PSI 340cc/min 200hp
  • 58 PSI 511cc/min 300hp

4 Cylinder NA (naturally aspirated) engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp


You only need to increase your exhaust if the current exhaust is creating a restriction.

On most factory exhausts you'll see your flow rate is still fine 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 generally help improve air flow out of the engine but avoid an exhaust that is too wide or you might just stuff your flow rate and make things worse. So generally speaking, keep to a size of 1.5 to around 2.5 inches to maximise flow rates, and this should take into account the amount of air your engine is moving.

Typically exhaust restrictions are in the catalyst and filters installed, so adding a higher flowing high performance aftermarket one will improve air flow, and rather than doing an illegal decat, will keep the car road legal.

Weak spots Issues & problem areas on the Theta

The Theta engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen as long as they are regularly serviced and maintained.

Carbon build up in the head, particularly around the valves which will sap power or create flat spots, this is a larger issue on direct injection engines but should be looked out for on all engines. We have tips on removing carbon build up.

Some of our members have had issues with flat spots or glitches after applying mods and upgrades or tuning, this is not usually related to this engines design, so instead see our article on diagnosing flat spots and problems after tuning which should help you get the bottom of this issue.

Regular oil changes are vital on the Theta, especially when tuned and will help extend the life and reliability of the engine.

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.

If you would like to know more, or just get some friendly advice 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.

Please help us improve these tips by sending us your feedback in the comments box below.

We love to hear what our visitors have got up to and which upgrades work best for you on your car. Which helps us keep our guides and tips up to date helping others with their modified car projects. Your feedback and comments are used to keep this page up to date, and help improve the accuracy of these articles which are kept updated and constantly revised.

If you've enjoyed this page we would be very grateful if you could share a link to it on your favourite forums or on your social media profiles, it helps us keep going.

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

PLEASE HELP: I NEED YOUR DONATIONS TO COVER THE COSTS OF RUNNING THIS SITE AND KEEP IT RUNNING. I do not charge you to access this website and it saves most TorqueCars readers $100's each year - but we are NON PROFIT and not even covering our costs. To keep us running PLEASE Donate here

If you liked this page please share it with your friends, drop a link to it in your favourite forum or use the bookmarking options to save it to your social media profile.

Feedback - What do You Think?

Please use our forums if you wish to ask a tuning question, and please note we do not sell parts or services, we are just an online magazine.

Help us improve, leave a suggestion or tip

Your Constructive comments on this article, I really want to improve this article with your help and suggestions.

Please watch this video and subscribe to my YouTube channel.

Member Benefits

Join our forum today and benefit from over 300,000 posts on tuning styling and friendly car banter.

You will also have full access to the modifed car gallery, project car updates and exclusive member only areas.

(All car owners of all ages and from all countries are welcome).

BMW 335i - 2021 COTY

We gave the BMW 335i our coveted car of the year award, read more about this awesome car and see why 335i Tuning Guide

Tips for N54 Tuning

Tips for N55 Tuning
Tips for B58 Tuning

Popular articles

Tuning Diesels
ECU Remapping
Double Clutch
Induction Kits
Customize a car
Chipping cars
Modified Car insurance
Track day insurance
Remapping Diesels
MPG calculator
DPF unblocking tips
Stage 1 Tuning

Stage 3 Tune

Stage 3 tune

Throttle Body

Throttle bodies

Body Kits

Car bodykits. Side skirts, sills, bumpers and wide body kits.

Car Stickers

Car stickers – vinyl printed stickers.

How To Clear A Blocked Dpf

How to clean a DPF

Handheld Ecu Mapping

ByteFlash Handheld DIY ECU mapping

MPG Calculator

MPG calculator UK miles per Gallon – calculate MPG