Tuning the Renault H4Jt

"Comprehensive guide to performance tuning the Renault H4Jt engine!"

We are frequently getting posts requesting information on the best H4Jt upgrades. So let us look into Renault H4Jt upgrades and outline the best upgrades on this great engine and point out some common pitfalls along the way.

Here we outline options for your H4Jt tuning and point out the ultimate mods that work. Renault H4Jt make awesome project engines and with carefully picked performance parts like remaps, turbo improvements and camshafts you will maximize your driving fun.

Just because particular tuning parts are popular with H4Jt owners it doesn't mean it is good, instead we'll concentrate) on the top tuning parts that will give your H4Jt the biggest power gain return for your cash.

Altering your H4Jt 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 camshafts tend to increase the performance across the rev range, you might lose a little bottom end bhp but the higher rpm power will improve.

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.

In a daily driver should ideally to match your power band to your preferences.

I'd be amazed if you have found a H4Jt Motorsport cam is a pleasure to live with when driving around busy urban areas.

Different H4Jt engines respond better to less aggressive camshaft durations check your engine on a rolling road.

The map and fuelling also will say much on the power gains you'll hit.

Longer 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.

H4Jt Tuning Stages

Stage 1 H4Jt modifications: Drilled & smoothed airbox, Panel air filters, Intake headers, Remaps/piggy back ECU, Sports exhaust manifold, Fast road camshaft.

Stage 2 H4Jt modifications: fuel pump upgrades, high flow fuel injectors, Fast road cam, Ported and polished head, induction kit, Sports catalyst & performance exhaust.

Stage 3 H4Jt modifications: Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Engine balancing & blueprinting, Crank and Piston upgrades to alter compression, Twin charging conversions, Internal engine upgrades (head flowing porting/bigger valves).

The H4Jt units are great to work on and we're finding that there are increasing numbers of modifications and tuning parts about.

A remap allows a tuner to unlock the full potential of all the parts you've done to your H4Jt.

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

Forcing more fuel and air into each cylinder is the aim to any car tuning job.

Intake take the air during the suck phase from the filter and allow it to be pulled into the engine and mixed with fuel.

The shape and flow characteristics of the Headers can make a large effect on to fuel engine efficiency on the H4Jt.

On popular production engines plenum chambers are in dire need of aftermarket tuning parts, although a few makers provide fairly well optimized plenum chambers.

Larger H4Jt valves, doing some 3 or 5 angle valve jobs and porting and head flowing will also raise torque, and as an added benefit will raise potential for increasing the torque increase on other tuning parts.

Turbo upgrades for the H4Jt

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 H4Jt

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

When the engine has forced induction tuning mods are more reliable and most turbocharged engines will have strengthened components.

However you'll find engines will need better parts at higher power limits

See where you'll find these limits and fit better quality components to handle the power.

There are many people spending a a stack of money on turbocharger upgrades on the H4Jt only to watch the motor throw a rod soon after it's been enthusiastically driven.

Larger upgraded turbo chargers will usually experience a bottom end lag, and smaller turbo chargers spool up more quickly but do not have the high rpm power band gains.

In recent times the choice of turbo chargers is always evolving and we now see variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end performance.

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

It is not unusual that there's a limitation in the air flow sensor AFM/MAF on the H4Jt when considerably more air is being sucked into the engine.

We see 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 harder to install. We have this article on twincharging if you want to read more.

Uprating H4Jt fuel injectors

Don't dismiss the need look at the fuel delivery when you are increasing the bhp and torque - it makes the car more thirsty. Don't forget to be generous with your injector capacity.

As a rule of thumb add 20% to the flow rate when specifying an injector, this takes into account injector deterioration and affords you some 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.

Best H4Jt performance exhausts

You should look to boost your exhaust if your exhaust is creating a restriction.

On most factory exhausts you should find that your flow rate is 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 help increase the flow of air through the engine.

But if the exhaust pipe is too large, ie: it's over 2.5 inches bore, you will lose a lot of your flow rate and end up losing power and torque.

Usual exhaust restrictions typically happen through the catalyst and or DPF filters which manufacturers fit, especially as they start to get worn and carbon builds up, so adding a faster flowing sports alternative will help avoid this restriction.

Problems and issues to look out for on the H4Jt

The H4Jt engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the H4Jt, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your H4Jt engine please join us in our friendly forum where you can discuss tuning options in more detail with our H4Jt 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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