Tuning Feature: Nissan VQ25VHR Modified

"Comprehensive guide to performance tuning the Nissan VQ25VHR engine!"

We are always seeing threads requesting information on the optimum VQ25VHR mods that work. So let us look into Nissan VQ25VHR parts and outline the best upgrades on this great engine and point out some frequent tuning mistakes along the way.

This six cylinder V block boasted many versions over it's production run and engine size ranged from 2 to 4 litres. Nissan produced a motorsport version badged as the VQ30DETT showing what this platform is capable of. Some of the 3.5 liter engines have pretty strong internals and can withstand up to 1000hp in ideal conditions, and parts from these high spec engines are often sourced and fitted into others accross the range.

The Nissan VQ25VHR offer good returns when tuned and with the best uprated upgrades like remapping, turbo kits and camshafts you will really maximise your driving opportunities.

Here we outline options for your VQ25VHR tuning and summarise the greatest upgrades.

Just because particular parts are popular with VQ25VHR owners it doesn't mean it is good, instead we will focus on the best parts to provide your VQ25VHR with the biggest power gain return for your cash.

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

NB: Fast road camshafts normally boost the bhp throughout the rev band, you may sacrifice a little bottom end bhp but higher rpm power will be lifted.

Race camshafts, boost the higher rpm power band but as a result the car will not idle smoothly and low end power nearly always suffers.

A Motorsport camshaft won't do well if in heavy traffic.

You should ideally optimize your engines power to your driving style so for a typical daily driver stick with a shorter duration VQ25VHR camshaft

Some VQ25VHR engines respond better to more or less aggressive cam durations so view each engine as unique.

The engine timing and fuelling also will make differences on the bhp gains you'll achieve.

A longer valve duration can alter the bhp 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.

VQ25VHR Tuning Stages

Stage 1 VQ25VHR modifications: Fast road camshaft, Intake headers, Panel air filters, Remaps/piggy back ECU, Sports exhaust manifold, Drilled & smoothed airbox.

Stage 2 VQ25VHR modifications: induction kit, Sports catalyst & performance exhaust, fuel pump upgrades, high flow fuel injectors, Fast road cam, Ported and polished head.

Stage 3 VQ25VHR modifications: Internal engine upgrades (head flowing porting/bigger valves), Adding or Upgrading forced induction (turbo/supercharger), Competition cam, Engine balancing & blueprinting, Twin charging conversions, Crank and Piston upgrades to alter compression.

The VQ25VHR engines respond well to mods and we note that there are plenty of modifications and performance parts around.

ECU flashing will help unlock the full potential of all the upgrades you've done to your VQ25VHR.

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 often depend much on the upgrades you've done and the condition of your engine.

It is the whole point to any engine tuning task to shove more fuel and air into the VQ25VHR engine

Headers carry the air from the filter and allow it to be drawn into the engine cylinders with fuel for the squish phase.

The bore size, shape and flow rate of the Headers can make a noticeable change to fuel atomisation on the VQ25VHR.

On popular production engines intake headers are crying out for aftermarket tuning parts, although some manufacturers provide reasonably good intake headers.

Fitting big valve kits, doing a bit of 3 or 5 angle valve jobs and porting and head flowing will also improve power, & more importantly will give you increasing the power increase on other tuning mods.

Turbo upgrades for the VQ25VHR

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 VQ25VHR

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

When an engine has a turbocharger parts are giving better power gains and we find turbo charged engines are built with uprated components.

There are tuning limits for every engine, with some being over specified and some just sufficiently able to handle stock power

Discover these limits and install higher quality crank and pistons to survive the power.

It's not unheard of drivers spending a loads on turbo upgrades on the VQ25VHR only to see the motor explode soon after it's been completed.

Large upgraded turbo units tend to experience no power at low rpm, and small turbo units spool up quickly but don't have the high rpm torque gains.

We are pleased that the choice of turbo units is always increasing and we now see variable vane turbo units, allowing the vane profile is altered according to speed to lower lag and increase top end performance.

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

It is not unusual that there's a restriction in the air flow sensor AFM/MAF on the VQ25VHR when considerably more air is being drawn into the engine.

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

Adding a supercharger or additional turbo will make large bhp gains, although more complex to configure. We have this article covering twinchargers if you want to read more.

Uprating VQ25VHR fuel injectors

When you boost the bhp you will need to uprate to the fuel system.

More bhp needs more fuel. Most tuners we speak with say to over specify your injector capacity.

As a rule of thumb add 20% when fitting an injector, this accounts for injector deterioration and gives 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 VQ25VHR performance exhausts

You should look to increase your exhaust if the current exhaust is actually causing a flow problem.

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

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

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

Problems and issues to look out for on the VQ25VHR

The VQ25VHR engines, if regularly serviced and maintained, are generally very reliable and have few issues. {But if neglected they can cost a small fortune|When neglected they get very expensive to run|They can however be quite expensive if neglected| }

Regular oil changes are vital on the VQ25VHR, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your VQ25VHR engine please join us in our friendly forum where you can discuss tuning options in more detail with our VQ25VHR 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 tuning mods were the most effective for them, it helps us improve our recommendations and articles to reflect current trends in modifications and ensures that our VQ25VHR guides and tips are kept up to date.

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