Modding tuning and best performance upgrades on the Renault H4Jt engine!

Tuners tips on "H4Jt Modifications"

H4Jt Modifications Guide

How to modify and upgrade the Renault H4Jt

"Comprehensive guide to tuning the Renault H4Jt engine!"

Our friends at TorqueCars often are getting emails asking how to improve the H4Jt from people inquiring about getting more power from the H4Jt and wanting to know what are the ultimate H4Jt mods that work. So let us look into Renault H4Jt mods and outline the best modifications on this great engine and point out some problems along the way.

We shall review and look at H4Jt tuning and point out the premier upgrades. Renault H4Jt are popular engines and with a few sensible upgrades like a remap, turbo improvements and camshafts you will certainly improve your driving fun.

Just because particular parts are appear in lots of H4Jt projects it doesn't mean it is good, so we'll concentrate on the ultimate parts that will give your H4Jt the best power gain for you money.

Without us subscribing to the mentality 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'.

H4Jt induction kits

Improving air intake on the H4Jt

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

So the fundamental goal to any performance tuning task to push air into your H4Jt but this has a knock on effect with the air flow sensor.

It is common that there is a limit in the air flow sensor AFM/MAP on the H4Jt when a lot more air is being drawn into the engine.

We see 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting power at a much lower level.

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

The bore size, shape and flow characteristics of the Intake can make a noticeable difference to to fuel engine efficiency on the H4Jt.

Commonly we find the air intake manifolds are ripe for performance upgrades, although some car makers provide well optimised air intake manifolds.

Adding a H4Jt larger valve kit, doing some 3 or 5 angle valve jobs and porting and head flowing will also boost bhp, & importantly will afford you raising the bhp increase on other parts.

H4Jt performance cam tips.

Some H4Jt engines respond better to more or less aggressive camshaft durations so view each engine as unique.

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

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.

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.

NB: Fast road camshafts tend to raise the power across the rev band, you may sacrifice a little low down torque but your higher rpm power will be higher.

Competition camshafts, raise 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 you need to match your power band to your preferences.

I'd be surprised if you find a H4Jt Race cam is a pleasure to live with when driving around busy urban areas.

Stage 1, 2 and 3 mods for the H4Jt

Stage 1 H4Jt parts:

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

Stage 2 H4Jt parts:

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

Stage 3 H4Jt parts:

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

The H4Jt engines respond well to mods and we're pleased to see that there is a lot of modifications and tuning parts around.

A remap should help to unlock the full potential of all the upgrades you've done to your H4Jt.

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 the outcome often differs on the upgrades you've carried out and the condition of your engine.

Turbo modifications on the H4Jt

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 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 superb power gains.

If an engine has a turbocharger parts are giving better power gains and we find turbocharged engines use harder and stronger components.

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

We recommend you find these limitations and upgrade to better quality components to survive the power.

We see many drivers spending a lots of money on turbocharger upgrades on the H4Jt only to have the car explode when it's been finished.

Large upgraded turbos will usually experience a bottom end lag, and small turbos spool up more quickly but won't have the top end power band gains.

In the last 10 years the market of turbo chargers is always improving and we now see variable vane turbo chargers, allowing the vane angle is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbo chargers divert the exhaust flow into 2 channels and flow these at differently angled vanes in the turbocharger. They also boost the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large performance gains, although more complex to setup. We have this in depth look at twinchargers if you want to read more.

Tips about fuel supply on the H4Jt

When you boost the bhp you will need to ramp up to the fuelling.

More bhp needs more fuel. Experienced tuners recommend to over specify your injector capacity.

The accepted safe increase is to add 15% when specifying an injector, which takes into account injector deterioration and provides 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 H4Jt performance exhaust upgrades

You may need to uprate your exhaust system with an upgraded one is if your current exhaust is actually causing a restriction.

On most factory exhausts you should find that 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.

Please dont run with the biggest exhaust you can get you'll slow up the exhaust flow rate - the best exhausts 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.

The usual suspects causing problems in your exhaust flow rate are traced to the catalyst installed, so adding a better flowing performance alternative will help avoid this restriction.

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

Faults issues and things to look out for on the H4Jt

Like most engines an H4Jt, 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 H4Jt, failure to do this will exacerbate engine wear, on a tuned H4Jt 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 H4Jt why not pop over to the forums at TorqueCars where you can chat about H4Jt tuning options and read about others projects who may be planning to do similar modifications on their H4Jt.

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