Modding uprating the Vauxhall C18NZ engine!

All you need to know about "C18NZ Modifications"

C18NZ Modifications Guide

How to modify and upgrade the Vauxhall C18NZ

"Comprehensive guide to tuning and performance parts on the Vauxhall C18NZ engine!"

Forums like the one at TorqueCars are always getting posts asking how to improve the C18NZ from people inquiring about getting more power from the C18NZ and wanting to know what are the best tips for C18NZ mods that work. So let us look into Vauxhall C18NZ upgrades and outline the best mods that work on this great engine and point out some problems along the way.

Let us look into C18NZ tuning and show the greatest mods that work. Vauxhall C18NZ make awesome project engines and with the ultimate upgrades like a remap, turbo kits and camshafts you will certainly maximise your driving opportunities.

When talking about the greatest parts for your C18NZ engine, we are going to concentrate on the upgrades that give the best power gain for you money.

C18NZ induction kits

Improving air intake on the C18NZ

You need fuel and air for an engine to work. If there is little supply of fuel then it will run lean, if there is too little air it runs rich losing power which risks damage to the C18NZ. We'll pick up on fuelling later in this article but for now we shall look at air supply.

So Forcing more air and fuel into your C18NZ is the main goal to any engine tuning job.

It is not unusual that there is a restriction in the air flow sensor MAP/MAF/AFM on the C18NZ when considerably more air is being drawn into the engine.

When tuning you may well find you need to get an air sensor or flow meter capable of upto 4 bars to cope with quite large power gains, whereas the OEM air sensor was restricting power at a much lower level.

Engines intake headers take the air from the filter and allow it to be sucked into the engine cylinders.

Shape and rate of flow of the Headers can make a large improvement to fuel mixing and power on the C18NZ.

It's not uncommon that intake headers are needing performance upgrades, although a few car makers provide reasonably well designed intake headers.

Increasing the C18NZ valve size, doing a bit of C18NZ port enlargement and head flowing will also boost bhp, and importantly will make space for increasing the bhp increase on other modifications.

C18NZ performance cam tips.

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

The ECU mapping and fuel pump and injectors also will make differences on the torque gains you'll hit.

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.

Significant air intake, and exhaust improvements on the C18NZ can be made from cam upgrades. Changing the cam profile alters the intake and exhaust durations on the engine and can dramatically change the bhp and power output.

NB: Fast road cams tend to push up the bhp over the rev band, you could drop a little low end power but your higher rpm power will be lifted.

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

A Competition camshaft won't do well if driving around busy urban areas.

You should ideally optimize your power band to your typical driving style so for a road car stick with a mild fast road C18NZ camshaft

Stage 1, 2 and 3 mods for the C18NZ

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 C18NZ parts:

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

Stage 2 C18NZ parts:

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

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

Stage 3 C18NZ parts:

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).

Review your options and then acquire your parts and set yourself a power target to avoid expensive mistakes.

ECU flashing will help to establish the full potential of all the upgrades you've done to your C18NZ.

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 end result often rely on the upgrades you've done and the condition of your engine.

Turbo modifications on the C18NZ

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 C18NZ.

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 an engine has forced induction tuning mods are simpler to install and we find turbo charged engines are built using strengthened components.

There are reliable limits for every engine, with some being extremely strong and some only just able to handle stock power

It is important to find these limitations and fit better quality crank and pistons to cope with the power.

It's not unheard of drivers spending a lots of money on turbo charger upgrades on the C18NZ only to suffer the humiliation of seeing the engine block explode on it's first outing after it's completed.

Bigger capacity turbochargers will usually experience a bottom end lag, and low capacity turbochargers spool up quickly but don't have the peak end bhp gains.

Thankfully 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 gases into two channels and push these at differently profiled vanes in the turbo. They also boost 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 install. We have this in depth look at twinchargers if you want to read more.

Tips about fuel supply on the C18NZ

When you lift the bhp and torque you will need to uprate to the fuel system.

More bhp and torque needs more fuel. Experienced tuners recommend to be generous with your flow rate on the injectors.

The accepted safe increase is to add 15% to the flow rate when buying an injector, which takes into account 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 C18NZ performance exhaust upgrades

Only look to uprate your exhaust system with an upgraded one is if your current exhaust is creating a restriction.

On most factory exhausts you'll see your flow rate is still 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 will certainly help air flow through the engine but do not go too wide or you could will reduce the flow rate. Stick to one and a half to two and half inches as a rule of thumb.

The usual suspects causing problems in your exhaust flow rate are in the filters installed, so adding a better flowing race 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 C18NZ

Like most engines an C18NZ, 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 C18NZ, failure to do this will exacerbate engine wear, on a tuned C18NZ 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 C18NZ why not pop over to the forums at TorqueCars where you can chat about C18NZ tuning options and read about others projects who may be planning to do similar modifications on their C18NZ.

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 C18NZ, 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