Hyundai Epsilon Tuning Tips

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

We examine the options for your Epsilon tuning and summarise the greatest upgrades. Hyundai Epsilon engines make for really good project cars and with carefully chosen modified tuning mods like a remap, turbo upgrades and camshafts you will certainly maximize your driving fun.

History of the Engine

  • G4HA 0.8L 54 hp at 6000 rpm 51 lbft at 4800 rpm 4 cylinder
  • G4HC  1.0L 61 hp  at 5700 rpm 81 lbft at 3000 rpm 4 cylinder
  • G4HG 1.1L 68 hp at 5500 rpm  72 lbft at 2800 rpm 4 cylinder
  • G3HG 0.8L 55 hp at 5500 rpm 55 lbft at 4000 rpm 3 cylinder

The Epsilon was replaced by the Kappa engine.

Best Epsilon parts

Just because a upgrades is popular with Epsilon owners it doesn't mean you should fit it, we will ultimate upgrades that will give your Epsilon the biggest power gain return for your cash.

The cam profile plays a big part in the engines power output so cam upgrades make quite a large difference. The intake and exhaust durations will alter depending on the chosen cam profile, so large engines power gains are on offer for cam upgrades.

Fast road camshafts tend to bump the power through the rev range, you might lose a little bottom end torque but the top end will be better.

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

For a daily driver must carefully try to optimize your engines power to your driving style.

You will never find a Competition cam is a pleasure to live with when driving around busy urban areas.

Each engine responds better to different camshaft durations so view each engine as unique.

The ECU mapping and injectors and fuel pump also will make differences on the torque gains you'll hit.

A longer valve duration 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.

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

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

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

The Epsilon engines are great to work on and we're pleased to see that there are plenty of parts and performance parts about.

remap should help to unlock the full potential of all the tuning parts you've done to your Epsilon.

It will usually give around 30% more power on turbocharged vehicles and 15% on NASP engines, but you mileage will vary depending on the tuning parts you've done and the condition of your engine.

Feeding more air into the Epsilon engine is the main goal to any engine performance tuning job.

Intake headers transmit the air during the suck phase from the air filter and allow it to be sucked into the engine cylinders with fuel for the squish phase.

Shape and flow characteristics of the Intake headers can make a noticeable effect on to fuel atomisation and engine efficiency on the Epsilon.

We often see intake are begging for aftermarket parts, although a few makers provide reasonably well designed intake.

Adding a Epsilon larger valve kit, getting port work and head flowing will also boost torque, the fantastic side effect is it will make space for an improved torque 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 Epsilon

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.

There are practical limits for every engine, with some being very over engineered and some only just able to handle stock power

We see many people spending a lot of money on turbo charger upgrades on the Epsilon only to watch the whole thing go up in smoke soon after it's been enthusiastically driven.

Bigger turbo units will usually experience no power at low rpm, and small turbo units spool up quickly but do not have the top end power band gains.

We are pleased that the range of turbo units is always improving and we commonly find variable vane turbo units, permitting the vane profile is altered according to speed to lower lag and increase top end bhp.

Twin scroll turbo units divert the exhaust gases into 2 channels and flow these at differently profiled vanes in the turbo charger. They also boost the scavenging effect of the engine.

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


Don't overlook the need to ramp up the fuel delivery when you are increasing the power - it makes the car more thirsty. It makes sense to be generous with your injector capacity.

As a rule of thumb add another 20% when buying an injector, which takes into account injector deterioration and allows a little 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 NASP engines

  • 58 PSI 140cc/min 100hp
  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp


You may need to boost your exhaust if the current exhaust is actually creating a restriction in flow.

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

Don't go with the biggest exhaust you can source you'll slow up the exhaust flow rate - the best exhausts for power gains are usually between 1 to 1.5 inches. It is the shape and material more than the bore size.

Typically exhaust restrictions are traced to the catalyst installed, so adding a faster flowing high performance alternative will help avoid this restriction.

Weak spots Issues & problem areas on the

The engines are generally reliable and solid as long as they are regularly serviced and maintained.

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

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.

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 parts work best for them on each model of car. Comments are used to improve the accuracy of these articles which are continually updated.



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