Volvo B6304S Tuning

"All you need to know about performance parts and tuning the Volvo B6304S engine!"

The Volvo B6304S offer good returns when tuned and with the right modified upgrades like remaps, turbo kits and camshafts you will greatly maximize your driving opportunities.

We shall detail the best approach to B6304S tuning and highlight the optimum upgrades.

History, Power & Specs of the B6304S Engine

204 PS (150 kW; 201 hp) at 5200 rpm with 267 Nm (197 lbft) of torque at 4100 rpm

Tuning the Volvo B6304S and best B6304S performance parts.

Best B6304S upgrades

When talking about the ultimate modifications for your B6304S engine, we are going to concentrate on the tuning mods that give the best value for money.

Significant gains on the B6304S can be made from cam upgrades. Altering the cam profile alters the intake and exhaust durations on the engine and can dramatically change the bhp and power output.

Fast road camshafts commonly increase the torque throughout the rev range, you may lose a little low end bhp but your higher rpm power will be higher.

Motorsport and 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.

On a car driven daily must carefully try to match your bhp range to your usage of the car.

I'd be surprised to hear from any driver that a B6304S Motorsport camshaft is a pleasure to live with when on the daily commute, because the lumpy idle will make the car prone to stall and smooth driving at low rpm becomes impossible. If you are developing a track car this doesn't matter as you are in the high end of your RPM range anyway and that is where you want the power to be.

Each engine responds better to more or less aggressive cam durations so set your engine up on a rolling road.

The ECU mapping and fuel pump and injectors also have an effect on the power gains you'll make.

Extending exhaust or intake 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.

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Best Engine Mods for your car

  1. Engine Tunes - engine tuning/remapping provides the most advantage in terms of cost savings,  aftermarket ECUs, and piggyback ECUs are all alternatives.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power. It is one of the most costly upgrades but provides the best gains.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.
  6. Typical stage 1 mods often include:
    Intake manifolds, Fast road camshaft, Sports exhaust header/manifold, drilled & smoothed airbox, Remaps/piggy back ECU, Panel air filters.

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

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

    The B6304S engine blocks make great tuning projects and we're pleased to see that there is a lot of parts and tuning parts around.

    A remap allows a tuner to establish the full potential of all the parts you've done to your B6304S. There are a few remappers out there that can map these engines (it might be the 5 cylinder ones though) motronic 4.4. I understand it is possible in most cases to replace the Motronic 4.3 with a 4.4 ECU for example and others have used the Megasquirt or Apexi as aftermarket ECU replacements.

    (In some cases, as the factory ECU is locked flashing is not an option, so an aftermarket ECU is the route to take, and many of these will outperform factory ECU's but make sure it has knock protection and that you get it setup properly.)

    It will usually give you around 30% more power on turbocharged vehicles and you can expect to see around 15% on NA (naturally aspirated) engines, but your mileage often differs on the parts you've applied and the condition of your engine.

    Feeding more air and fuel into each cylinder is the whole point to any engine modification task.

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

    Shape and rate of flow of the Intake can make a substantial change to fuel engine efficiency on the B6304S.

    Commonly we find the intake manifold are in dire need of aftermarket parts, although a few OEM provide well optimised intake manifold.

    Adding a B6304S larger valve kit, doing some port matching and head flowing will also raise bhp and torque, & importantly will make space for a greater bhp and torque increase on other tuning mods.

    B6304S Turbo upgrades

    NA (naturally aspirated) 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 B6304S

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

    If an engine is turbocharged, mods are giving better power gains and you will discover turbo charged engines are built with uprated components.

    There are reliable limits for every engine, with some being over specified and some just sufficiently able to handle stock powerDiscover these limits and upgrade to stronger pistons, crank and engine components to survive the power.

    The general consensus is that the gearbox and drivetrain will experience problems before the engine power limit is reached, particularly with automatic boxes.

    400bhp appears to be the point at which people start swapping in stronger cranks and pistons., I'd feel happier saying 300bhp, and you'll get good reliability, it depends how much you want to push it.

    We see many people spending a lot of money on turbo charger upgrades on the B6304S only to watch the motor explode soon after it's first rolling road session.

    Bigger upgraded turbo units tend to suffer no power at low rpm, and low capacity turbo units spool up much more quickly but don't have the top end bhp gains.

    Over the last 20 years the range of turbo chargers is always improving and we commonly find variable vane turbo chargers, where the vane profile is altered according to speed to lower lag and increase top end power.

    Twin scroll turbo chargers divert the exhaust flow into 2 channels and feed 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 limit in the air flow sensor AFM/MAF on the B6304S when considerably more air is being drawn into the engine.

    Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor sapped bhp at a much lower level.

    Adding a supercharger or additional turbo will make large bhp gains, although more challenging to setup. We have this feature on twinchargers if you want to read more.


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

    The accepted safe increase is to add 20% capacity when fitting an injector, which takes into account injector deterioration and provides a bit of 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.

    B6304S Performance Exhausts

    You only need to boost your exhaust if the existing exhaust is actually creating a restriction.

    On most factory exhausts you should find that your 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.

    Sports exhausts balance the flow of air through the engine.

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

    Usual exhaust restrictions can be traced to the emissions filters installed, so adding a better flowing race alternative such as a sports catalyst pretty much removes this restriction, thanks to it's larger size and surface area, and will effectively raise the performance to levels you would expect without having a catalyst installed, but keeps the car road legal.

    Weak spots, Issues & problem areas on the B6304S

    The B6304S engines are generally reliable and solid units, as long as you follow the manufacturers service schedules, and use a good quality oil to ensure longevity. Few problems should happen as long as they are regularly serviced and maintained.

    Carbon build up in the head, particularly around the valves which will sap power or create flat spots, this is a larger issue on direct injection engines but should be looked out for on all engines. We have tips on removing carbon build up.

    Some of our members have had issues with flat spots or glitches after applying mods and upgrades or tuning, this is not usually related to this engines design, so instead see our article on diagnosing flat spots and problems after tuning which should help you get the bottom of this issue.

    Regular oil changes are vital on the B6304S, especially when tuned and will help extend the life and reliability of the engine.

    If you would like to know more, or just get some friendly advice on Tuning your B6304S engine please join us in our car forums where you can discuss B6304S tuning options in more detail with our B6304S owners. It would also be worth reading our unbiased Volvo tuning articles to get insights into each modification and how effective they will be for your car.

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