Tuning Feature: Nissan VQ25HR Modified

"Comprehensive guide to tuning the Nissan VQ25HR engine!"

We are regularly seeing threads asking how to improve the VQ25HR from people wanting to know what are the premier VQ25HR mods that work. So let us look into Nissan VQ25HR parts and outline the best modifications on this great engine and point out some problems along the way.

This Nissan V6 boasted many versions over it's production run and cc ranged from two to four litres. Nissan came up with a Race ready version 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 VQ25HR make a good tuning project and with carefully chosen motorsport tuning mods like remapping, turbo upgrades and camshafts you will definitely improve your driving experience.

TorqueCars will look at VQ25HR tuning and summarise the optimum upgrades.

The ultimate VQ25HR parts on an engine are as we have found the ones that give the best power gain for you spend.

We won't be swayed by popular VQ25HR parts, they need to be cost effective.

The camshaft profile plays a big part in the engines power output so camshaft upgrades make quite a large difference. The intake and 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 usually raise the bhp and torque across the rev range, you may lose a little bottom end torque but the top end will be lifted.

Competition camshafts, raise the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

In a daily driver one, ideally, need to optimize your torque band to your cars usage.

I would be surprised if you have found a VQ25HR Competition cam is a pleasure to live with when in heavy traffic.

Some VQ25HR engines respond better to more aggressive camshaft durations so view each engine as unique.

The map and fuel pump and injectors also will say much on the bhp gains you'll get.

Altering valve durations 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.

VQ25HR Tuning Stages

Stage 1 VQ25HR modifications: Remaps/piggy back ECU, Sports exhaust manifold, Fast road camshaft, Intake headers, Panel air filters, Drilled & smoothed airbox.

Stage 2 VQ25HR modifications: high flow fuel injectors, induction kit, Fast road cam, Ported and polished head, Sports catalyst & performance exhaust, fuel pump upgrades.

Stage 3 VQ25HR modifications: Crank and Piston upgrades to alter compression, Engine balancing & blueprinting, Competition cam, Adding or Upgrading forced induction (turbo/supercharger), Twin charging conversions, Internal engine upgrades (head flowing porting/bigger valves).

ECU mapping allows a tuner to fully realize the full potential of all the tuning mods you've done to your VQ25HR.

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 will depend much on the tuning mods you've done and the condition of your engine.

It is the main goal to any tuning project to shove more fuel and air into each cylinder

Intake headers carry the air from the filter and allow it to be fed into the engine and mixed with fuel.

The size of bore and shape and flow characteristics of the Headers can make a large improvement to fuel delivery on the VQ25HR.

Commonly we find the intake headers are in dire need of performance upgrades, although a few makers provide fairly well optimized intake headers.

Adding a VQ25HR larger valve kit, doing a bit of 3 or 5 angle valve jobs and porting and head flowing will also improve power, & importantly will afford you raising the power increase on other parts.

Turbo upgrades for the VQ25HR

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 VQ25HR

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

If the engine has a turbo already fitted upgrades are giving better power gains and you will discover turbocharged engines will have 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 restrictions and upgrade to higher quality crank and pistons to utilize the power.

We've seen car owners spending a lot of money on turbocharger upgrades on the VQ25HR only to suffer the humiliation of seeing the car explode just after it's been completed.

Big capacity turbos often suffer no power at low rpm, and small turbos spool up really quickly but won't have the high rpm engines power gains.

Thanks to new tech the world of turbochargers is always increasing and we commonly find variable vane turbochargers, permitting the vane angle is altered according to speed to lower lag and increase top end bhp and torque.

Twin scroll turbochargers divert the exhaust gases into a couple of channels and feed these at differently designed vanes in the turbocharger. 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/MAP) on the VQ25HR when considerably more air is being sucked into the engine.

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

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

Uprating VQ25HR fuel injectors

Don't omit to increase the fuel system when you are increasing the bhp and torque - it makes the car more thirsty. It is important to be generous with your injectors flow rate.

The rule of thumb is to add 20% capacity when specifying an injector, this accounts for 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 VQ25HR performance exhausts

You only need to to upgrade your exhaust if your current exhaust is actually creating a flow problem.

On most factory exhausts you'll find the exhaust 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 balance the flow of gases through the engine.

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

Typically exhaust restrictions are traced to the emissions filters installed, so adding a higher flowing high performance alternative will help avoid this restriction.

Problems and issues to look out for on the VQ25HR

The VQ25HR 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 VQ25HR, particularly when the engine has been modified and is putting down more power than the manufacturer intended.

For more information on Tuning your VQ25HR engine please join us in our friendly forum where you can discuss tuning options in more detail with our VQ25HR 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 VQ25HR guides and tips are kept up to date.

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This article is flagged for an update, so please pass on specific tips below that I can include. All articles, and content was written by me, Waynne Smith TorqueCars founder. Some outlines are just too general so I appreciate your feedback and suggestions. This entry was filed under Nissan. You can leave a response below or join our forum to discuss this article and car modification in detail with our members.

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