Modding tuning and best performance upgrades on the Nissan VQ25HR engine!

Car tuning tips:VQ25HR Modifications"

VQ25HR Modifications Guide

How to modify and upgrade the Nissan VQ25HR

"Comprehensive guide to tuning the Nissan VQ25HR engine!"

TorqueCars are regularly seeing threads requesting information on how to improve the VQ25HR from people wanting to know what are the things tuners recommend when it comes to VQ25HR upgrades. 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.

The Nissan VQ25HR make a good tuning project and with carefully picked uprated tuning mods like a remap, turbo improvements and camshafts you will positively increase your driving enjoyment.

Our aim here is to detail the best approach to VQ25HR tuning and highlight the greatest upgrades.

The optimum VQ25HR parts on an engine are usually the ones that give the biggest return for your money.

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

VQ25HR induction kits

Improving air intake on the VQ25HR

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 little flow of air it runs rich resulting in lost power . We'll pick up on fuelling later in this article but for now we shall look at air supply.

So the goal to any performance tuning job to get air into your VQ25HR but this has a knock on effect with the air flow sensor.

It is common that there's a limit in the air flow sensor AFM/MAP on the VQ25HR 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.

Headers take the on the suck phase from the filter and allow it to be drawn into the engine cylinders.

The bore size, shape and rate of flow of the Air Intake manifolds can make a noticeable effect on to fuel atomisation and engine efficiency on the VQ25HR.

It's not uncommon that intake are ripe for an upgrade, although a few manufacturers provide reasonably good intake.

Increasing the VQ25HR valve size, getting VQ25HR port enlargement and head flowing will also raise torque, & more importantly will afford you a better torque increase on other upgrades.

VQ25HR performance cam tips.

Some VQ25HR engines respond better to different cam durations check your engine on a rolling road.

The engine timing and injectors and fuel pump also have an effect on the torque gains you'll make.

Extending exhaust or intake durations can alter the torque 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.

Altering your VQ25HR camshaft will make a dramatic difference to the engine engines power. Choosing a higher performance camshaft profile raises the engines power accordingly.

NB: Fast road camshafts normally raise the power through the rpm band, you could sacrifice a little low down power but the higher rpm power will be higher.

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

A Motorsport cam is not great driving around busy urban areas.

You should ideally optimize your engines power to your typical driving style so for a daily driver stick with a fast road VQ25HR cam

Stage 1, 2 and 3 mods for the VQ25HR

Stage 1 VQ25HR parts:

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

Stage 2 VQ25HR parts:

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

Stage 3 VQ25HR parts:

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

Plan your options and then buy your parts and set yourself a power target to avoid expensive mistakes.

Remapping will help to establish the full potential of all the tuning mods you've done to your VQ25HR.

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 may differs on the tuning mods you've fitted and the condition of your engine.

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

Turbo modifications on the VQ25HR

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 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 superb power gains.

When the engine is fitted with a turbo mods are going to make more power and we find turbocharged engines already contain strengthened components.

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

See where you'll find these limits and upgrade to forged components to handle the power.

We've seen mechanics spending a a stack of money on turbo upgrades on the VQ25HR only to suffer the indignity of watching the car throw a rod just after it's been completed.

Big capacity turbos tend to suffer a bottom end lag, and little turbos spool up much more quickly but won't have the top end engines power gains.

Thankfully the market of turbochargers is always moving on and we now see variable vane turbochargers, allowing the vane angle is altered according to speed to lower lag and increase top end power.

Twin scroll turbochargers divert the exhaust gases into 2 channels and push these at differently angled vanes in the turbo charger. They also help 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 and torque gains, although more challenging to get working. We have this article on twincharging if you want to read more.

Tips about fuel supply on the VQ25HR

You will need to ensure that the engine is not starved of fuel so need to uprate the fuelling when you start going beyond 20% of a bhp hike. We strongly recommend you to over specify your injectors flow rate.

The accepted safe increase is to add another 15% when buying an injector, this accounts for injector deterioration and gives a bit of 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 VQ25HR performance exhaust upgrades

We'd only recommend you look to replace your exhaust system with an upgraded one is if your exhaust is actually causing a restriction.

On most factory exhausts you should find that the exhaust flow rate is good 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 increase the flow of gases through the engine.

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

Typically exhaust restrictions are in the catalyst installed, so adding a freer flowing performance alternative will help avoid this restriction.

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

Faults issues and things to look out for on the VQ25HR

Like most engines an VQ25HR, 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 VQ25HR, failure to do this will exacerbate engine wear, on a tuned VQ25HR 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 VQ25HR why not pop over to the forums at TorqueCars where you can chat about VQ25HR tuning options and read about others projects who may be planning to do similar modifications on their VQ25HR.

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