MX5 Turbo Charging Forced Induction
Due to the overwhelming success of the original Christmas & New Year Holiday MX5 overview blog I have produced another exciting MX5 blog this time focused on forced induction, mainly turbo charging. Even at this basic level. 78.4% enjoyment guaranteed!*
(*blog enjoyment not quantifiable)
There are two types of forced induction; Supercharging and turbo charging. Supercharging involves forcing cold air into the engine from the air intake filter. Extra oxygen plus extra fuel and spark creates a bigger bang, thus creating more power. Turbo charging uses exhaust gases to spin a turbo turbine, forcing air back around into engine while drawing in air from the intake. Again extra oxygen plus extra fuel plus spark… POWER!!!!
What Is It…
A turbo is generally seen as the option for higher BHP figures. Supercharging produces a linear speed increase much like standard driving feel, just much faster. Turbo charging will give an instant power boost when the turbo spools up to the optimum RPM. Smaller turbos spool up quickly giving almost linear feel, but they can max out if you want to reach top speeds on boost. A larger turbo will introduce turbo lag (a delayed instant rush of power when the turbo kicks in from spooling to the optimum RPM) but will be able to achieve higher top end speeds.
I will try to cover as many of the basics, but be aware there are many additional features/upgrades you can add to a turbo charger install. You could spend £1500 on a budget or £7000+ on a top end install. It is always said you can only pick two of the following on a tight budget; cheap, reliable, fast.
I opted for cheap and reliable initially, but soon found this went out of the window when I also wanted fast which replaces the cheap part.
Firstly the turbo – A very popular option for the MX5 is a 2nd hand Subaru Impreza TD04 turbo. Big enough to give good top speeds, spools quickly (4k rpm) but with some kick due to the turbo lag, cheap and readily available off eBay or forums etc. Just make sure there is no play in the shaft when you buy one. A turbo will require a custom exhaust manifold and downpipe to exhaust, aftermarket air intake filter, as well water and oil feeds to cool the turbo.
A well designed turbo exhaust manifold is a huge topic alone, but the basics involve making sure all four branches from the exhaust ports to turbo are the same length, capable of withstanding the constant temp changes on a turbo. Temperatures at the manifold will easily reach 1000 degrees centigrade. A cheaper way is a log manifold. They are tried and tested and popular with DIY manifolds but they don’t allow equal pressure from each exhaust port as the distance from each port to turbo is different. A turbo forces the extremely hot exhaust gases back into the inlet manifold, so the air needs to be cooled to maximize performance and reliability. This requires an intercooler, which sits in front of the radiator, and all alloy/silicone pipework from turbo to intercooler back to the inlet manifold. An alternative is a basic cross over pipe usually only seen on superchargers, where the need to cool the air isn’t as necessary.
With the increase of oxygen this requires an increase of fuel. Among other things he stock ECU does not have the capacity to handle the increased fuel quantity required so an aftermarket ECU is required. The MegaSquirt range is very popular and has enough features to cover everything you could require. There are numerous versions, the more expensive, the more features you get such as launch control, multiple fuel maps for when driving off boost (low revs) then when on boost (high revs), various inputs/outputs to name a few. There are other more expensive ECUs also available.
The stock injectors will only be able to pump out a limited amount of fuel. If you want high BHP figures you will need to upgrade the injectors. RX8 yellow injectors are a straight swap for the stock ones and very popular. 2nd hand injectors may need testing and cleaning to ensure they are in tip top condition.
With the increase of air and fuel, the exhaust gases reading will now be out. On standard car the O2/Lambda sensor is known as a narrowband sensor. It reads only a narrow band of O2 figures. On a forced induction car the band of O2 figures can be vast so a wideband sensor is required which connects to the ECU. AEM sell a wideband with gauge which is widely used.
Increasing BHP way above stock levels means the clutch will start to slip. This could be at 160bhp, could be at 180bhp. It simply cannot cope with the added power. Aftermarket stage 2/3 clutches are required. The higher the BHP figure wanted the higher spec the clutch must be. Cheap eBay clutches like F1, PPC, XTD (they are all identical) have a somewhat good reputation, but they do require a change of driving style as they are 6 puck clutches resulting in the car juddering if revs are not high enough. To stick with the OEM clutch feel more money is required for a flyin miata clutch from the US.
Finally is a boost solenoid. A turbo has a wastegate (opens to the exhaust) which opens when the boost pressure reaches a desired figure, via an actuator. The higher the boost the faster you go. On a TD04 turbo for example the actuator is set to about 7 psi, so without a solenoid this is the max boost pressure you’ll achieve before the actuator opens the wastegate. When introducing a boost solenoid (a digital solenoid, not the cheap manual style option) the ECU will keep the solenoid closed until your desired PSI (set in the ECU) is reached thus increases boost and more speed.
That is all the basic bits covered. There are numerous other bits required, and the bigger the install you more parts you’ll find you need. If you plan to go on track with the car most people tend to fit a thick core alloy radiator and an oil cooler. As the turbo goes white hot both are a very good idea since the oil and coolant continue to cycle back around the engine. If installing an oil cooler be sure to buy a thermostatic plate. These make sure the oil is up to temperature before passing through the oil cooler. There is no point cooling cold oil further. Also any water that’s got into the system overnight or similar is burnt off by the hot oil.
But it’s not finished just yet. Once all installed you’ll need to have ECU mapped correctly. Base maps are available online but since every engine/turbo install is that little bit different a specialist is required to setup the ECU maps for fuel/spark/timing etc. ECU management software tunerstudio seems to be the go to software for tuning. It does have an autotune feature which will automatically map the basics of the car theoretically meaning you could drive the car to the garage. Unless you know what you are doing I would definitely suggest a professional tuning garage.
That’s it! The car should then be great fun to drive and will surprise most high performance car out there.
Turbo charged MX5’s are becoming increasingly popular and a recent article in a weekly car magazine shows this point.
Complete kits are also available or some garages offer a drive in, drive out service if you have no DIY skills or the time to do it. There are benefits of both, but I think if you opt for the DIY install, not only will it be cheaper but you’ll end up knowing the turbo setup backups, so should anything need adjusting or replacing you know exactly how to fix it.
Have a Merry MX5 Turbo Charging Christmas and 2015 !