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The big advantage of CDI is that the capacitor can be fully charged in a very short time (typically 1ms). This means that CDI is well suited to application where insufficient dwell time is available (i.e high-revving V8 engine using a single distributor).

Although the energy of a good inductive system can be equal to that of a CDI, there is one other consideration. The CDI may release the same amount of energy, but it does so over a much shorter duration. This means that the CDI has a more intense spark, but it does not last as long. This has both advantages and disadvantages.

The short spark duration is not good for lighting relatively lean mixtures as used at low power level. As a result misfire may occur. To help this problem many CDI ignitions release multiple sparks at low engine speeds. This multiple spark discharge method is where the company MSD got its name. The idea is that if the engine misfires on the first spark then one of the subsequent sparks should ignite. Another approach is to use an inductive ignition at low rpm and switch to a capacitive ignition at high rpm (as claimed by the HKS TwinPower).

The intense spark of a CDI is very good at igniting mixtures under high loads. This makes CDI well suited to firing a plug under very high levels of boost pressure, or with water injection or overly rich air/fuel ratios.

CDIs do generate very high levels of electromagnetic noise and this is the main reason why CDIs are rarely used by automobile manufacturers. However if good wiring loom layout and other suppression techniques are observed then CDIs may be used with any engine management system with very good results.

CDI coils
As mentioned earlier, CDI coils do not use the inductance of the coil to store energy. Therefore a good CDI coil has very different properties when compared to a good inductive ignition coil. Very low inductance coils may be used to produce the most intense (but shortest duration) spark. Using a conventional inductive coil with CDI releases the spark energy over a longer duration which can be a good or bad thing depending on the application.

The Ultimate CDI System
As with inductive systems, the ultimate CDI systems use a single coil per cylinder. These coils can be driven quite hard has they only have to fire once per 720 degree engine cycle and have time in-between to cool. Unfortunately, this requires a multiple channel CDI which doesn’t come cheap. Typically it is this added cost which sways many of our customers towards a well-setup inductive system.

Kerry Bartlett drove the car in the 2006/2007 Sport Saloons class and won the series outright.

Kerry also took the Capacity class (T1 1850-3000cc turbo) and Handicap Sport Saloon championships as well as 5 out of 6 pole positions along the way.

The car and engine were built by Kirk McLaren and of course the tuning was done by NZEFI.

Performance
555hp at rear wheels at 18psi boost = over 600hp at the flywheel, .
Lap times: Teretonga 1:02.7, Ruapuna 1:30.2, Levels 1:07.5
252km/hr (157mph) on main straight at Teretonga.

Engine
Mazda 13B Rotary Turbo, JC Cosmo end housings, Batman rotor housings, Ceramic 2-piece apex seals, Montgomery stud kit, Precision Engineering 2-piece centre bearing crank, lightened 9.0CR batman rotors, RX8 stationary gears. Turbo-port. Balanced rotating assembly. Engine built by Kirk McLaren

Induction
HKS T04Z roller bearing turbo, HKS GTII 60mm external wastegate. Stainless tuned length exhaust manifold. 3.5″ main exhaust system with custom made aluminium muffler. 2.5″ wastegate exhaust. Trust 600x300x100 Intercooler

Fuel system
Custom built tuned length inlet manifold with 80mm throttle body, 2x 1680cc Bosch secondary injectors & 2x Sard 1000cc primary injectors. Sard fuel pressure regulator. 2x Bosch motorsport efi pumps, custom 33L alloy fuel tank. Aeroquip fuel lines. Greedy BOV. Samco silicon hoses, 3″ alloy intercooler pipes, Pipercross air filter.

Engine management
MoTeC engine management & MoTeC SDL Dash/data logger.

Transmission
Holinger H6S 6-speed Sequential gearbox.

Clutch
AP twin plate clutch, Precision Engineering molly nitrided flywheel.

Diff
Mazdaspeed 2-way plate type Lsd with 3.9, 4.1, 4.3, 4.4 or 4.8 ratios.

Suspension
HKS externally adjustable shocks, HKS height adjusters & strut tops. Fully fabricated alloy/molly suspension arms and hubs, adjustable molly sway bars. Relocated suspension mounting points.

Brakes
Front, Alcon Mono-4, monoblock differential bore 4-pot callipers with 335mm x 30mm Alcon vented disks. Rear, Brembo differential bore 4-pot callipers with 310mm x 21mm vented disks, Driver adjustable peddle box.

Bodyshell
Fully lightened & seam welded/gusseted with multi point cage. Montgomery Motorsport glass bonnet, guards, hatch & doors.

Interior
Racepro race seat, Sabelt 5-point harness.

Aero
Montgomery Motorsport adjustable rear wing. Vielside side skirts and C-West dam/splitter, C-West canards.

Wheels/tyres
Rays MS01 17×9 front & 17×9 rear with
Kumho V700 255/40/17′s (Sport Saloons control tyre)

Cooling
J-Win 50mm core V-mounted radiator with alloy tanks, standard oil coolers.

Some older pictures of the car from before we broke the 500hp mark.

Work started with demolishing the chemical washbay that the previous tenants had used. This was useful because it also means they had installed a sump and drains in the dyno room area. Then the room was framed up and lined with 18mm MDF for soundproofing. The entire room frame is completely separate from the rest of the building which stops sound being conducted through the frame.

An air conditioning fan was sourced from a secondhand dealer. It has a 4kW motor, which we have a variable speed drive for, and according to our calculations flows around 20 000 CFM, or enough to change the air in the room around 10 times a minute. The fan came with a muffler and some ductwork which was reused.

The rest of the extraction system was fabricated and lined with sound deadening material. This is the piece that sticks out through the roof.

Then all the ductwork was cleaned up and painted. A supporting structure was designed and fabricated to hold it.

The ductwork was then mounted on the frame, with the cap sticking through the roof. This involved a fair bit of effort with a forklift, and plenty of beer.

The end result is a fantastic addition to the Sydenham skyline. Well we think that, at least.

Meanwhile, the room was being used for woodworking duties, making the rest of the inlet and extraction ducting out of MDF. The support in the middle of the room was used to keep the ceiling joists straight while loading them with the ductwork. The hoses hanging from the ceiling are the water lines for each of the 4 dyno pods.

On top of the room is the inlet duct and plenum. The plenum is used as a baffle to cut down on the noise travelling back up the inlet to the front of the room. These are the ducts from the plenum to the front of the room.

This is the view of the same ducts from the front of the room, looking up.

This is the front of the plenum showing the air filter mounts, and internal rubber baffling.

Before (above) and after (below); this shows the extent of the ductwork. You can just see the plenum, the ductwork at the back of the room is the start of the extraction which then goes through the fan and out the roof. Air is drawn into the plenum, and then is ducted to the front of the room. This ensures airflow through the room to keep the temperature constant and air clean.

A separate exhaust system was then fabricated. It uses a 44 gallon drum as a muffler and has a roof mounted fan drawing exhaust gas through it on the roof, so sucks up most of the exhaust gas. Exhaust gas inside the room is ducted to this through flexible ducting, hung over the exhaust.

The exhaust has several chambers and is packed with fire rated pink batts, it has great attenuation characteristics and should flow enough for a 1000hp engine (~2000 CFM).

Detail of the remainder of the exhaust system. The fan is roof mounted.

One of the tireless workers who we are grateful to. Also thanks to Kris, Nick M, Jamie and others, your help is appreciated!

The room in use, testing a customer’s BMW CSi Turbo.

Feb 2007 – Now with doors.

Hanging the 1.5m wide dyno doors proved to be quite an effort.

But the end result is great. Finally the room is fully functional. Still requires the trim around the doors which will seal the room, at the moment there are still a few air leaks.

Jonathon became the first customers car to be tuned in the new (very unfinished) dyno room.

THIS DIAGRAM WILL BE ADDED SOON!

When the igniter supplies a ground the coil charges. When the igniter removes the ground the spark is generated. The length of time that the coil charges for is called the dwell time and is measured in thousands of a second or milliseconds (ms).

The igniter also limits the coil current to a predetermined value. This limiting feature provides protection of the coils if the dwell time is set too high. It is possible to get igniters with different current limits. Different types exist which limit anywhere between 6-10A. There are also some igniters with no current limiting and particular care must be taken when using these.

An ignition channel is required for each coil. So on multiple coil ignition setups a multi-channel igniter is required. Never run more than one coil off a single igniter channel.

Coil Requirements for Inductive Ignition Systems

For maximum spark energy coils designed for high-energy transistor/inductive ignition systems must be used. These have a primary winding resistance of between 0.4 and 1.0 Ohms. The coil must also have sufficient inductance (although this is much harder to measure) as it is the inductance of the ignition coil that is used to store the energy. The amount of energy stored in the coil (in Joules) is given by the following equation:

THIS EQUATION WILL BE ADDED SOON

L is the inductance (measured in Henries) of the coil’s primary winding, while I (measured in Amps) is the current flowing in the primary winding before the coil is fired. This equation shows that to get more spark energy you can either choose a coil with a higher inductance or pump the coil up to a higher current.

Although a coil with more inductance will store more energy than one with low inductance, it will also take longer to charge assuming the resistances are the same. As a result it needs more dwell time to be available. In an application where the coil must fire very often (i.e a V8 using a single distributor) it may be impossible to achieve this dwell time at high rpm. In this case choosing the coil with more inductance will result in less spark energy at high rpm. This is because the coil will not reach maximum current and the current is more important than the inductance (because of the squared term in the equation).

The current may be increased by increasing the dwell time provided the igniter has not reached its current limit. This means that there is no point using 5ms of dwell on a coil that charges to 9A in 5ms if the igniter in question limits at 7A. All this will do is make the igniter run hotter – no extra ignition energy will be produced. So you can see that the ideal dwell time is not just a function of the coil but the igniter too! Even if the igniter is not limiting the current, the extra ignition energy comes at a price. The heat dissipated by the coil goes up with the square of the current too! This means that there is much higher risk of burning the coil out, especially in distributor applications which must fire very often.

Also remember that the available dwell time will drop of at high rpm on distributor applications. This problem is much worse on engines with a high number of cylinders. As a general rule a distributor fed 4 cylinder will start to drop dwell at 7000rpm, while the dwell on a single distributor 8 cylinder engine will start to drop off at 3500rpm! This is the reason why any high performance V8 needs either a dual-distributor setup, multiple coils or a capacitor discharge ignition (CDI) system.

The Ultimate Inductive Ignition System

The ultimate inductive ignition system uses direct spark with one high-inductance coil per spark plug. Each coil only needs to fire once during each 720 degree engine cycle so there is plenty of time to charge the coils even at ultra-high rpm. Each coil may be charged to a higher current than in a distributor application because the coil is firing less often and has time between firings to cool. Such a system is capable of storing and delivering as much energy as a good capacitive (CDI) setup.

Although “coil-on-plug” types do not need an HT lead, these are not ideal because the space constraints make it difficult to design a high inductance coil. As a result these typically these have low-inductance (they charge very quickly). Their small size also makes them incapable of handling the increased heat that results from using high current/dwell. The result is that these typically store and release about half as much energy of a good coil being charged to higher current.

We feel that “coil-near-plug” with a much better coil more than makes up for having to use a very short HT lead. This opinion is reflected in the line-up of ignition products that we offer to our customers.