Modifying and improving: "Theta Modifications"

Theta Modifications Guide

How to modify and upgrade the Hyundai Theta

"Comprehensive guide to tuning the Hyundai Theta engine!"

Our friends at TorqueCars are regularly getting emails requesting info on how to improve the Theta from people wanting to know what are the best Theta power upgrades. So let us look into Hyundai Theta upgrades and outline the best modifications on this great engine and point out some potential pitfalls along the way.

The Hyundai Theta are good project engines and with the right uprated parts like remaps, turbo kits and camshafts you will maximize your driving fun.

We shall detail the best approach to Theta tuning and point out the ultimate modifications.

Just because particular parts are popular with Theta owners it doesn't mean you should fit it, instead we will concentrate on the best parts that will give your Theta the best power gain for you spend.

Without us subscribing to the misaprehension of 'if it's shiny and makes more noise it must be good' you seem to get in many tuning magazines and on car forums'.

Theta induction kits

Improving air intake on the Theta

You need fuel and air for an engine to work. If there is too little fuel then it will run lean, if there is not enough air it runs rich sapping power . We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Getting air into each cylinder is vital to any engine tuning project.

You'll commonly see there is a limit in the air flow sensor AFM/MAF on the Theta when a lot more air is being pulled into the engine.

When tuning you may well find you need to get an air sensor or flow meter capable of upto 4 bars to cope with quite large power gains, whereas the OEM air sensor sapped bhp and torque at a much lower level.

Intake flow the air from the filter and allow it to be drawn into the engine cylinders.

The bore size, shape and rate of flow of the Air Intake manifolds can make a large change to fuel engine efficiency on the Theta.

We often see intake headers are crying out for a performance upgrade, although some makers provide decently flowing intake headers.

Increasing the Theta valve size, doing some port work and head flowing will also lift torque, & more importantly will raise potential for a greater torque increase on other tuning mods.

Theta performance cam tips.

Some Theta engines respond better to more or less aggressive camshaft durations so set your engine up on a rolling road.

The ecu map and fuel pump and injectors also will make differences on the torque gains you'll make.

Longer valve durations can alter the torque 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.

Altering your Theta cam will make a dramatic difference to the engine power band. Choosing a higher performance cam profile raises the power band accordingly.

NB: Fast road cams normally raise the bhp over the rev band, you might lose a little low end power but the top end will be better.

Competition cams, raise the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

On a car used daily you should ideally to match your engines power to your usage of the car.

I would be surprised if you have ever thought a Theta Competition cam is a pleasure to live with when on the daily commute.

Stage 1, 2 and 3 mods for the Theta

Stage 1 Theta parts:

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

Stage 2 Theta parts:

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

Stage 3 Theta parts:

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

The Theta units are fantastic to work on and we see that there are plenty of mods and tuning parts around.

A remap helps unlock the full potential of all the parts you've done to your Theta.

Tuning tips and articles Engine tuning Transmission tuning Care care Intake & exhaust mods Improve handling Forums

You will typically expect to see gains of approximately 20-30% more power on turbocharged vehicles and you can expect to see around 15% on NASP engines, but power output often vary depending on the parts you've applied and the condition of your engine.

Turbo modifications on the Theta

To get a turbo working on a NASP engine there is a lot involved, from lowering compression ratio to improved fuel supply and mapping, so we have found a great guide to helpavoid the common pitfalls or end up with an unfinished project because you were not told what you were getting into by doing this on the 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 major power gains.

If an engine is turbo charged upgrades are going to make more power and turbocharged engines use better components.

There are reliable limits for every engine, with some being extremely strong and some only just able to handle stock power

It is important to find these limitations and fit higher quality crank and pistons to handle the power.

There are many people spending a lot of money on turbo upgrades on the Theta only to watch the engine block go up in smoke when it's used on the roads.

Large turbos will usually suffer low end lag, and small turbos spool up much more quickly but won't have the peak end power band gains.

Thanks to progress the selection of turbochargers is always improving and we commonly find variable vane turbochargers, where the vane angle is altered according to speed to lower lag and increase top end power.

Twin scroll turbochargers divert the exhaust flow into two channels and flow these at differently profiled vanes in the turbo charger. They also help the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large bhp and torque gains, although more challenging to get working. We have this article covering twinchargers if you want to read more.

Tips about fuel supply on the Theta

You will need to ensure that the engine is not starved of fuel so should look at the fuelling when you start extending past 20% of a power hike. It makes sense to be generous with your injectors flow rate.

The rule of thumb is to add 20% when specifying an injector, this takes into account injector deterioration and affords some spare capacity should the engine need more fuel.

Don't forget that different fuel grades will usually require different settings, a high octane fuel will burn more efficiently than lower octane fuel for example. A car will trim fuel supply to keep within the ideal air fuel mix but at the extreme ends you may need to adjust your injector capacity, or the mapping or you'll get flat spots and potential lean or rich fuel issues..

Recommended Theta performance exhaust upgrades

The only time you should look to boost your exhaust system with an upgraded one is if the existing exhaust is actually creating a restriction in flow.

On most factory exhausts you'll find your flow rate is fine even on modest power gains, but on a serious tuning project with a big boost in power you will certainly need to get a better flowing exhaust.

Do not go with the biggest exhaust you can find this will slow the exhaust rate - the best for power gains are usually between one and a half to two and half inches. Your exhaust design, the bend angles and construction are what have more effect on flow rates than your pipe width to a certain extent. So the exhaust design is a big factor.

Typically exhaust restrictions can be traced to the filters installed, so adding a freer flowing performance alternative will help avoid this restriction.

Decatting (NB:catalysts reduce harmful engine emissions) is illegal in most countries and regions.

Faults issues and things to look out for on the Theta

Like most engines an Theta, should have few issues if it gets properly serviced and looked after.

We cannot stress enough the need for oil changes with the correct grade of oil on the Theta, failure to do this will exacerbate engine wear, on a tuned Theta this is more important than ever and close attention should be paid to your maintenance schedule.

If you are interested in learning more or getting impartial tuning advice for your Theta why not pop over to the forums at TorqueCars where you can chat about Theta tuning options and read about others projects who may be planning to do similar modifications on their Theta.

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