Tuning the Renault H4Bt

"Comprehensive guide to tuning the Renault H4Bt engine!"

We are regularly getting messages about the things we are recommending when it comes to H4Bt modifications. So let us look into Renault H4Bt mods and outline the best modifications on this great engine and point out some frequent tuning mistakes along the way.

The Renault H4Bt are good project engines and with the optimum modifications like ECU maps, turbo upgrades and camshafts you will dramatically increase your driving pleasure.

We shall provide a guide to H4Bt tuning and highlight the best modifications.

When talking about the optimum parts for your H4Bt engine, we are going to focus on the modifications that give the best power gain for you money.

Altering your H4Bt cam will make a dramatic difference to the engine bhp. Choosing a higher performance cam profile raises the bhp accordingly.

NB: Fast road cams tend to increase the bhp through the rev band, you may lose a little bottom end torque but your higher rpm power will be better.

Motorsport cams, increase the higher rpm power 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 cars usage.

I'd never have found a H4Bt Motorsport and race cam is a pleasure to live with when driving around busy urban areas.

Each engine responds better to different camshaft durations than others.

The engine timing and injectors and fuel pump 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.

H4Bt Tuning Stages

Stage 1 H4Bt modifications: Drilled & smoothed airbox, Fast road camshaft, Remaps/piggy back ECU, Intake headers, Sports exhaust manifold, Panel air filters.

Stage 2 H4Bt modifications: high flow fuel injectors, induction kit, Fast road cam, fuel pump upgrades, Ported and polished head, Sports catalyst & performance exhaust.

Stage 3 H4Bt modifications: Internal engine upgrades (head flowing porting/bigger valves), Crank and Piston upgrades to alter compression, Competition cam, Engine balancing & blueprinting, Adding or Upgrading forced induction (turbo/supercharger), Twin charging conversions.

The H4Bt units respond well to mods and we're finding that there is an increase of parts and performance parts out there.

A remap will help fully realize the full potential of all the tuning parts you've done to your H4Bt.

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

It is the whole point to any engine upgrade project to force more fuel and air into each cylinder

Air Intake manifolds flow the air from the filter and allow it to be pulled into the engine cylinders.

Structure and rate of flow of the Plenum can make a substantial difference to to fuel mixing and power on the H4Bt.

We often see intake are improved through aftermarket tuning parts, although a few car makers provide reasonably good intake.

Fitting big valve kits, doing a bit of H4Bt port enlargement and head flowing will also lift power, the fantastic side effect is it will permit an improved power increase on other parts.

Turbo upgrades for the H4Bt

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 H4Bt

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 a car has a turbo already fitted upgrades are more reliable and turbocharged engines are made using better components.

There are common areas of failure for every engine, with some being over specified and some only just able to handle stock power

Research these limitations and install higher quality crank and pistons to utilize the power.

We see many people spending a loads of money on turbocharger upgrades on the H4Bt only to watch the engine go up in smoke on it's first outing after it's used in anger.

Bigger turbos commonly experience low end lag, and small turbos spool up much more quickly but won't have the top end engines power gains.

In recent times the selection of turbos is always evolving and we commonly find variable vane turbos, where the vane angle is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbos divert the exhaust flow into two channels and direct these at differently designed vanes in the turbocharger. They also increase the scavenging effect of the engine.

It is not unusual that there is a limit in the air flow sensor (AFM/MAF/MAP) on the H4Bt when loads 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 was restricting bhp and torque at a much lower level.

Adding a supercharger or additional turbo will make large bhp gains, although harder to install. We have this in depth look at twinchargers if you want to read more.

Uprating H4Bt fuel injectors

Don't forget to boost the fuel system when you are increasing the performance - it makes the car more thirsty. Most tuners we speak with say to be generous with your flow rate on the injectors.

The rule of thumb is to add 20% when buying an injector, this allows for injector deterioration and provides some spare capacity should the engine need 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 H4Bt performance exhausts

You may need to replace your exhaust if the existing exhaust is creating a restriction.

On most factory exhausts you should find that your flow rate is still ok 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 largest exhaust you can source you'll slow the exhaust rate - the best for power gains are usually between 1.5 to 2.5 inches. It is the shape and material more than the bore size.

Usual exhaust restrictions come around the filters installed, so adding a higher flowing high performance alternative will help avoid this restriction.

Problems and issues to look out for on the H4Bt

The H4Bt engines, if regularly serviced and maintained, are generally very reliable and have few issues.

Regular oil changes are vital on the H4Bt, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your H4Bt engine please join us in our friendly forum where you can discuss tuning options in more detail with our H4Bt 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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We really like hearing from our readers, and hearing about which parts were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our H4Bt guides and tips are kept up to date.

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