Jonty's MR2 Turbo

Spark plugs

It's not widely known that spark plugs have heat grades and are sometimes referred to as hot or cold.  Cars with high performance engines typically generate more heat and therefore require a colder plug to avoid it [the plug] getting too hot and igniting the fuel-air mixture before the spark fires.  A colder grade plug is a reflection of its ability to conduct heat away from the electrode tip and back into the block.

Being a grey import, trying to find plugs for an MR2 Turbo at most local auto-factors can sometimes prove to be a bit of a challenge, however, most guides will indicate that an alternative plug for the naturally aspirated MkII happens to be the primary one for the Celica GT4 which shares the same 3S-GTE engine as the MR2 Turbo.  Result!

Previously running with some NGK BKR7EVX plugs, I've reverted back to Champion Double-Copper ones to see how they get on.  Although the NGK's are a grade colder than stock, with the Champions designed for the 240 bhp Celica GT4 they should be fine and perform with no problems.

Finally, when thinking about which performance plugs to get, don't be too hasty to spend £50 or more on a set.  Copper is a better conductor of electricity than platinum or iridium and sets of copper plugs costing £10 that need changing every 10,000 miles will perform much better than those designed to be changed every 60,000 miles.

High pressure radiator cap

Most of the chemical energy in petrol is converted into heat and it's the job of the coolant system to get rid of it.  As a rough gauge, engines run best when the coolant is at about 93 degrees Celsius, or 200 degrees Fahrenheit.  Given that engines may be asked to work in the extremities of freezing or baking hot conditions, coolant must have not only a very low freezing point but also a high boiling point and the ability to absorb lots of heat.

Water is one of the most effective fluids for holding heat but its freezing point is too high and boiling point too low.  Nowadays a mixture of ethylene glycol (antifreeze), water, and anti-corrosion additives are used.  An example is Toyota's Forlife coolant.  Liquid under pressure has its boiling point raised which is essential given that coolant not under pressure could reach 250 to 275 F (121 to 135 C) causing it to boil.  Cooling systems are pressurised using a radiator cap (a glorified pressure release valve) to about 14 psi which raises the boiling point another 45 F (25 C) so the coolant can withstand higher temperatures.

The stock radiator cap from an MR2 Turbo pressurises the system to 13 psi.  Toyota Racing Development's (TRD) high pressure radiator cap operates at almost 22 psi, raising the boiling point even higher, which is useful for a high performance engine generating offensive amounts of heat (but important to note that all the components within the cooling system need to be in good working order to withstand the higher pressures).

Silicon intercooler hoses

Although more of a cosmetic modification, these new hoses help to restore some efficiency having dispensed with the old rubber pipe-work which was beginning to split, crumble, and distort.  Made from silicon, these attractive hose sections are present just after the turbocharger, to and from the intercooler, and finally into the throttle body.

Helix clutch

During a couple of motorway journeys I'd noticed that on the odd occasion the engine raced away when trying to accelerate.  Climbing engine revs with no increase in speed of the car is a tell-tale sign of a slipping clutch.  Ignoring a failing clutch will eventually lead to problems such as an inability to overtake, climb hills, pull-away, and possible damage to the flywheel. It's best to get it replaced sooner rather than later which is exactly what I did.

The standard Turbo clutch is good for 250 bhp (with similar torque values) however with the car already delivering power in this region, I thought it wise to aim for something slightly better.  Fensport sell Helix clutches, one of which is a 'fast road' kit and good for 270lb/ft of torque.  It's a 4-paddle design drive plate with a modified Toyota cover from the Celica GT4.

Above you can see the original clutch plate on the left -- it's very worn.  The new Helix plate on the right has an obvious design contrast -- less being more, I hope!  Manufactured with a rigid adapter plate, it incorporates cerametallic pads which keep their friction properties to a much higher temperature.

Fitting took an entire day, requiring the exhaust to be dismantled, engine dropped, and naturally the gearbox removed.  Apparently for a non-professional a day to do this is a major achievement!

Transmission fluid

The MR2 gearbox has a tendency to feel notchy and a popular choice is the use of Red Line transmission fluid to help smooth matters.  For gearboxes with the standard Toyota LSD or none at all, Red Line's MT-90 is a popular choice.  Their 75W90NS flavour is more suited to aftermarket LSD units.

The fluid itself was obtained from Delta Oil Ltd (a European distributor for Red Line) and at the time of writing, IMOC-UK members can expect a 20% discount off the normal retail price.

PCV catch-can

Crankcase gases are piped back into the air intake on all MR2 Turbos.  This process is called positive crankcase ventilation (PCV) and improves emissions but has a detrimental effect on performance as oil particles and hydrocarbons reduce power by lowering the fuel's octane level.  It also means hotter air is being fed into where it's not wanted.

Installing a catch-can (fitted as standard on Rev3+) allows oil and dirt to be collected, effectively cleaning the air before it's fed back into the intake (and also allows it to cool slightly).  The solution above was fabricated using a can obtained from Halfords and two new PCV hoses from Toyota.  Periodically the can just needs a clean inside.

A'PEXi air induction kit

All MR2 Turbos are afflicted with restrictive air boxes.  The solution is to discard the original setup in favour of a freer-flowing filter.  Although the MR2's entire engine bay may look small and cluttered there's a more than adequate air intake on the near-side that can force air straight into a cone filter.

Not happy with an oiled cotton gauze filter I opted for an A'PEXi Power Intake because dirt retention oil from wet filters can get into and hinder the air flow meter (AFM).  The A'PEXi filter, like most aftermarket ones, is designed to be unrestrictive therefore throttle, turbo response, and power are all improved.  Another bonus is the terrific sound of air being dragged into the turbocharger against its will.

The clumsy standard air and resonator boxes can be seen in the picture on the left.  When it comes to looks, compared to the A'PEXi there's just no competition.  With the kit, the AFM is still present (it has to be with a Rev1/2) and is but a supplied pipe that mates the filter to the air flow meter, with brackets for support.  The A'PEXi kit is superbly crafted and is regarded as the best filter on the market due to its excellent filtering ability and competitive price.

Turbocharger boost pressure

Rev1 and Rev2 MR2 Turbos can generate 220 bhp in standard form.  Due to changes in engine design, Rev3 onward Turbos generate 240 bhp.  The Rev1/2 Turbos achieve their power using a CT-26 twin-entry, ceramic turbo running at 10 psi.  The extra power from the Rev3+ was primarily the result of a smaller CT-20 turbo running at 13 psi.

With a turbocharged forced induction engine, the simplest way to increase power is to raise the turbo's maximum boost pressure.  This is a very cost-effective and rewarding modification which requires a fuel-cut solution, a bit of fiddling, and a little common sense if you wish to avoid expensive repair bills.

How is maximum boost achieved..?  By using a waste gate and an ECU-controlled bleed valve called the T-VSV, the two devices work together to maintain a maximum pressure of 10 psi or 13 psi, depending on revision of MR2.  When a pre-set limit of pressure is reached the waste gate opens so that the pressure in the turbo does not continue to rise -- sending the turbo and engine components into oblivion.

And how is the boost increased..?  A relatively inexpensive method of increasing boost without the need for expensive electronics is to fit a manual boost controller such as a bleed or Grainger valve (also known as a G-valve).  Both are adjustable, allow the control of pressure seen by the actuator, but work in slightly different ways.

Both devices sit in the pressure feed between the turbo and actuator.  Using the bleed valve as an example, as the turbocharger boost increases, a small amount of pressure is also escaping from the bleed valve (which is adjustable).  This escaping pressure is used to trick the actuator into thinking there is less boost pressure in the turbo than there actually is.  As the actuator will only open the waste gate once a pre-defined level of pressure is reached, the turbo will continue to build boost pressure.

My MR2 was originally fitted with a bleed valve which was later replaced with a G-valve.  Pressure is always escaping via the bleed valve and therefore the level is always acting on the actuator as boost pressure builds -- basically not very efficient.  With a G-valve however, this is not the case as the valve only opens when a level of pressure is reached.

A Grainger valve operates using a spring and ball-bearing -- when the G-valve is wound open the strength of the spring is small therefore it doesn't take much effort to squash the spring and move the ball bearing to open the valve.  As the valve is wound shut the strength of the spring increases, taking more effort to move the ball.  With careful adjustment the resultant turbo pressure can accurately be increased or decreased.

I'm currently running my standard turbo at 14 psi maximum boost.

Turbocharger pressure VSV (T-VSV)

This is the MR2's Turbo Variable Solenoid Valve, commonly known as the T-VSV.  This is a bleed valve which runs with the waste gate and controlled by the ECU and will drop the boost pressure (by closing) if a safety scenario is detected, e.g. low air temperature, low engine temperature, or detonation.  The T-VSV will ensure maximum boost cannot be achieved until operating conditions are favourable again.

With the T-VSV operational, approximately 4 psi of boost pressure can be bled and it is therefore recommended that the T-VSV be disabled when using a G-valve boost controller to avoid boost spiking.  As for the safety feature, with a boost gauge in place an eye can be kept on pressure levels at all times and if the engine is either cold or being subjected to very cold air temperatures then some common sense can be used when asking the turbo to work hard.

Disabling the T-VSV is easy.  A pressure feed runs from the actuator to the T-VSV which if cut and blocked, prevents the valve from seeing pressure and therefore remains permanently open.

NOTE: The T-VSV should NOT be disabled for a stock setup as doing so will leave the turbo running reduced boost pressure.

Stainless steel exhaust

The standard Turbo exhaust is extremely rigid and it's not uncommon to find one lasting a good 10 years.  With my own starting to show signs of age (although still MOT-friendly), I decided to replace it.  Mongoose stainless steel systems had always attracted my attention during my Rover ownership days and fabricate systems for the MR2, however people report that the tips are too close to the bumper and burning of the paintwork can occur.

After some research I decided to have a system made up by Hayward & Scott.  These systems can be a little expensive but are of excellent design and quality.  The way I see it, if you're going to spend a fair bit of money in one hit then you may as well do things right first time.

Out with the old and in with the new, the system is a free-flow, Y-design with twin polished back boxes.  Although the system had already been blue-printed it was still possible for me to specify my own requirements -- I opted for loudness not much greater than standard, 3.5in rolled-in tail-pipes, and removal of my catalytic converter.  The end result was one very sexy looking, superb sounding, performance enhancing exhaust system.

De-cat pipe

Catalytic converters weren't invented for performance reasons but for the benefit of the environment which is an annoyance for performance engines.  If it wasn't for the fact that they prevent a number of horrible chemicals entering the atmosphere, they'd literally be totally useless.  Due to their design, they're extremely restrictive when hot exhaust gases are trying to escape very, very quickly.

Given a loophole in the UK MOT, MR2 Turbos registered on or before 31st July 1995 can rightfully have their Cat removed.  If you're wondering how this is possible, as there is no exact engine/chassis match in the DoT database, a non-Cat emissions test can be conducted.

When Hayward & Scott crafted one of their fine exhaust systems for me, my MR2's Cat was also removed and replaced with a straight-through de-Cat pipe (and the catalytic converter put into storage in my garage).  The benefits of a performance exhaust and no catalytic converter restricting gas flow are phenomenal -- fuel economy, faster turbo spool-up, extra bhp, and improved power delivery.

Copper contact dizzy cap

The distributor cap (also referred to as a dizzy cap) is one of the three main components which serve to get each spark plug to literally 'spark' and ignite the fuel-air mixture.  The other two components are the rotor arm and HT leads -- both of which are difficult to upgrade and simply need to be replaced when worn.  The dizzy cap however can be uprated to a certain degree.

Copper is an excellent conductor and by adding copper contacts to a dizzy cap its transfer of electricity is improved.  Another advantage is that the standard contacts degrade very quickly and after 6 months can have an excessive amount of oxidisation build-up.  With copper, this doesn't happen.

Pictured above, the standard cap on the left shows the build-up that has to be literally cut away, leaving the contacts as they should be.  Copper contacts will stay cleaner and more conductive for much, much longer.

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