Help - Performance

The Help & How To guide for MX-5 Performance.

Turbochargers






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Superchargers






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Cold Air Induction






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Air Intakes






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Air Filters






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Water Injection






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Nitros Oxide






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THE FACTS

  • It's a cryogenic gas composed of nitrogen & oxygen molecules
  • It's 36% oxygen by weight
  • It's non-flammable when by itself
  • It's stored as a compressed gas between 750 & 900psi
  • The gas must be turned off when not required as gas leaking into the engine could result in an EXPLOSION when the engine is fired up.

The Basics

The nitrous is stored in a bottle at about 750psi. The gas is fed through 2 solenoids, the first solenoid is opened by an arming switch which also supplies a micro switch fitted to the throttle linkage, which is set at full throttle. The gas flows to the next solenoid via a T-piece which incorporates a nitrous regulator. The regulator bleeds-off a small amount of nitrous(50psi), which is teed into the pipe between the fuel pressure regulator and the plenum. Operated by negative pressure in the plenum chamber, with the throttle shut, the throttle body's butterfly creates a vacuum in the plenum chamber. As the throttle opens the vacuum reduces until almost 0, this allows the regulator to close which increases the pressure at the injectors. The un-used fuel is used to increase fuelling, by shutting the fuel regulator using nitrous pressure. The actual pressure applied to the fuel regulator is controlled by a jet. The jet takes a controlled amount of gas away from the fuel regulator. With nitrous holding the fuel regulator shut, closing the return line, the pressure in the fuel line increases. The pressure triggers the in-line fuel pressure switch when it reaches about 70psi, which then triggers the 2nd solenoid when at full throttle (micro switch is made), this allows the nitrous oxide to flow into the engine.
The fuel pump needs to deliver 1/2lb of fuel per bhp at 75psi.
An up-rated clutch may be required with the extra 50-80bhp.

Performance Tuning






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There are numerous ways to improve the performance of yourself and your car, in order to obtain low lap times.

 The first and most important thing that needs tuning is your mind. It provides by far the most significant improvements in lap times. Buy a good book on racecraft and read and digest it's contents. Then rethink each of your laps and how you would apply the techniques. Keep repeating this at home and when you next get to track start doing it. You will be amazed at how your lap times improve.

Ultra high performance tyres - Yokohama Advan A032R's. These types of tyres are really made for road race / rallying whilst being road legal. They have very large tread blocks and are quite soft with lot's of grip. They are worth around 2 seconds a lap. Other tyres are available with even better grip, such as Dunlop D98J

Setting up the geometry of the suspension / wheels, for toe out / in, camber and caster. One set of guide lines previously published in the NSW newsletter states:

Þ   Front Caster:                  +4.7o to +5.5o (whatever the maximum attained is)

Þ   Front Camber:                –0.6o to -.8o (this number varies with the caster)

Þ   Front Toe:                      1/16" per side, or 1/8" total toe OUT

Þ   Rear Camber:                 -1.1o

Þ   Rear Toe:                        1/16" per side, or 1/8" total toe IN, or zero.

 

The next most significant area is suspension – stiffer sway bars, adjustable shock absorbers (e.g. Koni's), stiffer shocks (e.g. Bilstein), stiffer springs (eg. King Springs) and  shorter springs to reduce ride height.

Note: Ride height and anti roll stiffness play a significant part in the speed at which a corner can be taken.

Fitting a limited slip differential will assist in getting the power to the ground when leaving sharp corners.

The recommended sequence is:

Þ   Air box & filter – improves top end breathing allowing the engine to rev more freely above 4500rpm to the red line. It also helps provide cold air from outside the engine bay and improves air flow through a large air opening and reducing the number of bends in the air flow.

Þ   Exhaust – high gas flow, improves removal of exhaust gases at high revs, reduces back pressure on engine

Þ   Extractors and wide bore exhaust pipe – tuned extractors improve torque and assist exhaust gas removal

Þ   Catalytic converter – wide bore to match exhaust pipe, improving gas flow

Note: These changes should not affect either warranty or insurance. It's quite likely that will want to make these changes first because they sound great and get the car off the mark quicker. However, for improving lap times it's certainly not the first thing you should spend money on. It's not the power of the car that matters, it's how you can handle the car that makes the real difference.

Then the serious (read expensive) engine modifications to increase power output – such as computer chips, programmable race computer, individual throttle bodies, aggressive camshafts, turbo and supercharger.

Note: Most if not all of these changes can / will almost certainly affect warranty, insurance and the class into which the car can be entered for supersprints or racing.

 

1.1.           Suspension Tuning

The standard MX5 suspension set up is excellent and provides a well balanced car on the race track. However, should you decide to change to high performance tyres, or different wheels or change the ride height or alter any of the suspension components then expect the balance of the car and it's "feel" to change. Often, this can be for the worse, introducing unwanted oversteer or understeer.

Whenever you make a change to anything affecting the tyres, wheels or suspension you should always retune the car to produce the best handling. If you don't, and improved performance was your aim, you may well have just wasted your money.

Below is a list of things you can do to restore your car to the same or better level of balance and handling:

 

 

Reduces Oversteer

Reduces Understeer

Tyre pressures 
                Front
                Rear

   
Reduce pressure
Increase pressure

   
Increase pressure
Reduce pressure

Tyre footprint size 
                Front tyre
                Rear tyre

   
Reduce tyre size
Increase tyre size

   
Increase tyre size
Reduce tyre size

Springs 
                Front Spring Rate
                Rear Spring Rate

   
Stiffer springs
Softer springs

   
Softer springs
Stiffer springs

Wheel Alignment Angles 
                Front Camber
                Front Caster
                Rear Camber

   
Less negative
Less positive
More negative

   
More negative
More positive
Less negative

Roll Centre  
                Front Height
                Rear Height

   
Raise height
Lower height

   
Lower height
Raise height

Track Width 
                Front
                Rear

   
Reduce track width
Increase track width

   
Increase track width
Reduce track width

  Note:  
Extremely low tyre pressures can be dangerous and excessive reduction in spring rates or sway bar stiffness will change the footprint of the tyre and can make the original problem worse.

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