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Dodging Defects

How to modify your car without attracting unwanted police attention...

By Michael Knowling

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At a glance...

  • How to modify your car and attract minimal police attention
  • Stealth mods - the name of the game!
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There are some cold hard facts to face up to when you modify a car.

When you modify a car in any way the probability of being pulled over and issued with a defect notice shoots through the roof. Equally disturbing is rate at which insurance companies wiggle out of making good a claim when your vehicle has been tinkered with. Oh, yeah, and try having your car repaired under warranty when you’ve got a bunch of go-fast bits bolted on...

Yep, you really are up against it when you decide to modify your ride.

But don’t take your bat and ball and run away just yet!

The chance of being stung by a defect, insurance or a warranty issues depends heavily on your approach to vehicle modification.

In many instances, there’s no reason why you can’t enjoy the same increased power output – but without anyone knowing about it. That's not to say that you should set out to deceive - there could be severe legal consequences. But if no-one asks what's been done to your car, well...

Don’t Attract Unwanted Attention!

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Vehicle modification is largely influenced by fashion and, at the moment, it’s fashionable to have plenty of ‘bling’ – the more shiny stuff, the better.

Bling is all you need to attract attention while cruising, but all too often it attracts the people you want to breeze straight past – the police.

It’s a simple fact - the more overtly modified your vehicle, the higher the probability of being pulled over.

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A list of defect-magnets include... Polished canon mufflers, blow-off valves and front-mount intercoolers, a too-low ride height, illegal wheel size/offset and dangerously mounted interior gauges.

And don’t forget the basics – it’s easy to overlook stuff like inoperative lights and bald tyres!

A Subtle Approach to Mods

To avoid defects and other car-mod related headaches, we suggest you integrate vehicle mods so they’re barely perceptible to an observer.

Strive to keep your car looking standard – after all, not many people get pulled over in a stocker (unless they are doing something silly!)

So how do you integrate mods, you ask?

Well, let’s start with the preliminary go-fast bolt-ons – the exhaust and air intake...

Stealth Exhaust Upgrades

First, your upgrade exhaust should not be loud enough to draw attention and it must meet tailpipe noise regulations. This is essential. Straight-through mufflers and resonators (which cause almost no flow restriction) should be used extensively. Another alternative is to use a variable back-pressure valve (see Butterfly Effect.)

The pipe diameter of your upgrade exhaust shouldn’t be excessive. A 4 inch exhaust is overkill for a mildly modified Subaru WRX – all it does is add noise and advertise your mods. Note that the layout of the exhaust is also important – it should follow the factory path to help go unnoticed.

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When the bonnet is opened, it’s also wise to have any aftermarket-looking headers or dump pipes covered with heat shields. If the standard heat shield won’t fit with the new exhaust, you may need to fabricate a custom shield. This photo shows a standard dump pipe heat shield being modified to fit an upgrade exhaust.

Finally, you should resist all temptation to go for a polished canon muffler. Sure, go for a high-quality looking muffler - but not something that offers hardly any noise suppression and stands out like you-know-whats.

Remember – you don’t want to be noticed!

Our Stealth Pintara Exhaust Upgrade

When we upgraded the exhaust on our Nissan Pintara Ti 2.4, the main criterion was to keep noise virtually standard and not to draw any attention.

Here is how we did it...

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After assessing various OE mufflers, we selected a rear muffler from a R33 Nissan Skyline Turbo. This muffler is similarly sized to the standard Pintara muffler and, once its dual outlets were relocated to fit neatly inside the standard bumper cut-out, you’d never pick anything had been done to the system. It looks like a factory ‘sports’ exhaust.

And did we achieve any significant performance gains?

We sure did. By fitting an OE Holden cat, new 2 ½ inch pipework and the R33 rear muffler, we slashed peak exhaust backpressure from 40 kPa to 10 kPa!

See Lung Transplant for full details.

Stealth Air Intake Upgrades

In order to maintain a factory under-bonnet appearance, it’s inevitable that you’ll need to use an airbox.

And that’s no bad thing.

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In most vehicles, the factory airbox can be modified to accept a large diameter feed pipe which replaces the factory snorkel. The feed pipe you make – or buy – should be made from black plastic or be painted ‘stealth black’ so it goes undetected.

Once a large diameter feed pipe has been fitted, total airbox restriction should be only a few inches of water pressure. In addition, you can replace the factory air filter element with an aftermarket drop-in filter - but don’t expect to pick up much power.

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The induction path from the airbox to the throttle – or the turbo – should then be examined on a case-by-case basis. Often, heavily convoluted sections of tube can be replaced with smooth-wall tube which reduces intake turbulence. Black rubber or plastic pipe can be used for this purpose. Note that the gains achieved by doing this are often greater than you’ll achieve with an aftermarket panel filter.

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Vehicles equipped with a hotwire airflow meter can benefit from the removal of the wire screen(s) that protect the sensing element. These screens cause a considerable flow restriction and their removal is undetectable unless the intake system is dismantled. Note that changes to mixtures and ignition timing may occur when the screens are removed.

Oh, and let’s look at one of the less popular induction mods – a larger throttle body.

A larger throttle body serves to provide greater response and torque at part-throttle positions and causes less restriction at full power.

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In many instances, a larger diameter throttle can be bolted on from other vehicles – for example, the entire Nissan/Holden RB30 throttle body bolts on to the Nissan E15 turbo engine. Where a factory upgrade is unavailable, your existing throttle body can be bored out a few millimetres and fitted with a larger diameter butterfly.

Nobody would have any idea.

Our Stealth VL Turbo Intake Upgrade

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The Holden VL Commodore Turbo air intake system responds very well to the modifications described.

Fitting a 100mm feed pipe to the bottom of the airbox, replacing the pipe to the turbocharger and removing the airflow meter screens dropped peak intake restriction from 29.5 to 13 inches of water – a 56 percent reduction in restriction!

What’s more, these mods went completely unnoticed by everyone who ever looked under the bonnet!

See Modifying the VL Turbo Intake for full details.

Stealth Boost Upgrades

If you own a turbo car, there are many ways to increase boost pressure.

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One of the least obtrusive is to insert a small restrictor (like seen here) in the hose from the turbo compressor outlet. The pill serves to control the amount of air bled by the factory boost control solenoid. This mod is completely invisible even during a detailed inspection – your car will just have a few psi extra boost for no apparent reason!

Alternatively, boost pressure can be increased in a late-model turbo car using electronic methods. And this brings us on to our next topic...

Stealth Engine Management Upgrades

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The most difficult to find engine management upgrade is a re-write of the factory ECU (ie a chip). A chip allows you to make changes to mixtures, timing, boost pressure and various other parameters – and none of the changes can be detected unless somebody accesses the ECU.

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An interceptor module is generally easy to detect - any aftermarket labelled computer and the splicing of wires is a dead give-away. Note that a plug-in adapter loom can be used to install an interceptor to some popular vehicles – this eliminates the need to cut any of the factory loom, bringing the mod one step closer to stealth.

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Aftermarket ECUs – which, if you read closely are suited for off-road use only – are easily identifiable. Their aftermarket enclosure is the biggest telltale. Most systems also require a MAP signal hose from the engine bay to the computer - we are led to believe that such a hose is illegal.

Stealth Intercooler Upgrades

If you’ve got a polished front-mount intercooler that required hacking half the bumper away, you’re asking for trouble. Accept it.

A better approach is to conceal the upgrade intercooler core behind the factory bodywork. Paint the core black so that it matches the car’s radiator and air conditioning cores and keep it tucked in behind the bumper and you should be right.

Intercooler plumbing can also be made to look factory. All you need is black-painted steel pipe and black rubber hose joiners. Make sure you keep the pipe route neatly arranged.

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This photo shows a very neat aftermarket turbo kit – note the black rubber intercooler pipes, which look entirely factory.

Oh and, since we’re in the area of intercooler piping, we should mention blow-off valves.

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If you absolutely must have one, you’re best bet is to use a recirculating valve (one that vents charge-air back to the turbo inlet). Note that atmospheric-venting blow-off valves are illegal in most areas. The black blow-off valves fitted to various Saabs and Japanese import engines are relatively easy to integrate to look factory. A pair of OE blow-off valves can be used in extreme applications.

But we must stress, if you’ve got the ‘pssht’ thing happening, you really are asking for a defect.

Stealth Modifications at Their Best

One of our favourite aftermarket power-up kits is the APS ‘Phase’ upgrade for the Ford XR6 Turbo. It’s worthwhile looking closely at these kits to appreciate how nicely the mods are integrated...

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The Phase 2 kit comprises a UniChip interceptor, free-flow exhaust, air intake, bigger injectors and an additional fuel pump. These mods give the XR6T 280kW at the back wheels (about 100kW more than a stocker!) with barely a hint of any aftermarket tinkering. The exhaust is easily within legal noise requirements and the only other visible mod is a replacement snorkel into the airbox.

You’d never pick it.

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The Phase 3 kit is even more impressive. We’ve seen a Phase 3 kitted XR6T crank a massive 327kW at the wheels (that’s almost double factory power!) and it wouldn’t get a second glance from the boys in blue. That 100 percent power gain is evident only by the upgraded exhaust and intake snorkel from Phase 2 plus a replacement wastegate actuator and front-mount intercooler kit.

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The wastegate actuator upgrade could be identified by only the keenest-eyed XR6T aficionado and – more impressively – the entire front-mount intercooler kit looks entirely factory. The black painted bar-and-plate core is completely stealth, as is the associated pipework. Even the hose clamps match the originals!

You could just imagine how the conversation would go if the car ever did get pulled over.

“Yes, officer, it’s all standard under the bonnet.

“What’s that? Well, um, that’s my friend’s 11 second time slip...”

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