Modding upgrading and tuning the Nissan VQ25VHR engine!

Car tuning tips:VQ25VHR Modifications"

VQ25VHR Modifications Guide

How to modify and upgrade the Nissan VQ25VHR

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

Sites like TorqueCars often are seeing threads asking how to improve the VQ25VHR from people wanting to know what are the premier VQ25VHR modifications. So let us look into Nissan VQ25VHR parts and outline the best modifications on this great engine and point out some common pitfalls along the way.

The Nissan VQ25VHR offer good returns when tuned and with carefully picked performance upgrades like remapping, turbo improvements and camshafts you will substantially improve your driving fun.

Here we look into VQ25VHR tuning and point out the best mods that work.

Just because particular modifications are popular with VQ25VHR owners it doesn't mean it is good, so we'll focus on the top modifications that will give your VQ25VHR the biggest power gain return for your cash.

Without us subscribing to the common myth 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'.

VQ25VHR induction kits

Improving air intake on the VQ25VHR

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

So Feeding air and fuel into your VQ25VHR is the main goal to any engine modification task.

You'll commonly see there is a limit in the air flow sensor (AFM/MAF/MAP) on the VQ25VHR when considerably more air is being fed into the engine.

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

Engines intake headers transmit the on the suck phase from the air filter and allow it to be fed into the engine cylinders.

Shape and rate of flow of the Intake can make a large difference to to fuel delivery on the VQ25VHR.

On popular production engines intake are in dire need of motorsport parts, although a few makers provide reasonably well designed intake.

Big valve conversions on the VQ25VHR, carrying out VQ25VHR port enlargement and head flowing will also improve power, and importantly will afford you a better power increase on other tuning parts.

VQ25VHR performance cam tips.

Different VQ25VHR engines respond better to mild camshaft durations so set your engine up on a rolling road.

The engine timing and injectors and fuel pump also have a large bearing on the bhp gains you'll get.

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.

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

NB: Fast road cams tend to push up the power through the rev range, you might lose a little low end power but top end will be higher.

Motorsport and race cams, push up the top end band but as a result the car will not idle smoothly and low end power nearly always suffers.

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

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

Stage 1, 2 and 3 mods for the VQ25VHR

Before we break the best tuning upgrades down into stages of tune, let's list the most effective tuning upgrades for you.

  1. Suspension Upgrades - always improve your cars handling
  2. Brake Upgrades - Even before adding power improve those brakes
  3. Intake - make sure the intake is not restricted, use filters and intake upgrades to improve this
  4. Exhaust - as with 3 ensure there is not restriction in the exhaust, cats are the usual bottleneck
  5. Tunes - remapping, piggyback ECU's and aftermarket ECU's can all make decent gains
  6. Fuelling - when you've increased power you'll need to match this with more fuel
  7. Turbo upgrades - Improving the intake with a large turbo and better flowing intercooler will be the biggest power gain you'll see (but one of the most complex).

This video guide to tuning cars is a great starting point to work from in your project.

Stage 1 VQ25VHR parts:

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

Tuning tips and articles Engine tuning Transmission tuning Care care Intake & exhaust mods Improve handling Forums

Stage 2 VQ25VHR parts:

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

Stage 3 VQ25VHR parts:

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

The VQ25VHR power trains are fantastic to work on and we see that there is a lot of mods and performance parts around.

ECU flashing should help to fully realize the full potential of all the upgrades you've done to your VQ25VHR.

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 usually depend much on the upgrades you've applied and the condition of your engine.

Turbo modifications on the VQ25VHR

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 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 impressive power gains.

When your car is fitted with a turbo modifications are giving better power gains and we find turbocharged engines are made with strengthened components.

There are tuning limits for every engine, with some being very over engineered and some only just able to handle stock power

We recommend you find these restrictions and fit better quality components to utilize the power.

There are many people spending a loads on turbo upgrades on the VQ25VHR only to experience the engine block go up in smoke just after it's been completed.

Big turbo units often suffer low end lag, and smaller turbo units spool up more quickly but do not have the peak end torque gains.

Thanks to progress the choice of turbo units is always improving and we commonly find variable vane turbo units, permitting 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 a couple of channels and feed these at differently designed vanes in the turbo. They also increase the scavenging effect of the engine.

Beefing up the air intake by adding a supercharger or additional turbo will help you achieve very large bhp gains, although harder to get working. We have this feature on twinchargers if you want to read more.

Tips about fuel supply on the VQ25VHR

You will need to ensure that the engine is not starved of fuel so will have to look at the fuelling when you start going beyond 20% of a bhp and torque hike. It is important to be generous with your injectors flow rate.

As a rule of thumb add 15% to the flow rate when specifying an injector, this takes into account injector deterioration and gives 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 VQ25VHR performance exhaust upgrades

Only look to upgrade your exhaust system with an upgraded one is if your current exhaust is actually causing a restriction.

On most factory exhausts you'll find the flow rate is still ok 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.

Sports exhausts generally help improve air flow through the engine but avoid an exhaust that is too large or you could will reduce the flow rate. Stick to one and a half to two and half inches as a rule of thumb.

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

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

Faults issues and things to look out for on the VQ25VHR

Like most engines an VQ25VHR, 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 VQ25VHR, failure to do this will exacerbate engine wear, on a tuned VQ25VHR 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 VQ25VHR why not pop over to the forums at TorqueCars where you can chat about VQ25VHR tuning options and read about others projects who may be planning to do similar modifications on their VQ25VHR.

We need your help to complete and improve this page, so do give us your feedback in the comments box below.

We want to know your experiences with upgrades on your VQ25VHR, it helps us improve our tips and keeps us current so please use the comments box to drop a tip.

If you liked this page please share it with your friends, drop a link to it in your favourite forum or use the bookmarking options to save it to your social media profile.

Check out TorqueCars new YouTube channel, and see their awesome new content...


Please use our forums if you wish to ask a tuning question, and please note we do not sell parts or services, we are just an online magazine.

Help us improve, leave a suggestion or tip

Your Constructive comments on this article