How a Turbocharger Works
The way a turbocharger works is pretty simple. The engine’s hot exhaust gases are captured and circulated through the turbine before being emitted back into the regular exhaust path and out of the tail pipes. The motion and heat of the exhaust gases cause the turbine to spin. The turbine is coupled to a secondary compressor via a shaft, and as the turbine spins, this output shaft spins in conjunction and subsequently turns the compressor blades as well. The compressor draws in fresh air and, as the name implies, packs the cylinders with air at a positive pressure, called boost (measured in PSI). Going back to our basic engine principle, the more air we can shove into a cylinder, the more fuel we can mix and ignite. It is a simple concept that works marvellously well. Turbochargers can add anywhere from 70hp to a couple hundred, depending on what size turbo is used as well what engine modifications are in place.
Fox Mustang Turbos: Hot Side vs Cold Side
Anyone that has or is currently installing a turbocharging system on their Fox Body has at one point or another mentioned the hot and cold sides of their system. Not only does it show technical prowess, but the distinction between the two is pretty important. To clear up any questions regarding these turbo terms, the "hot side" simply refers to the turbine and all piping associated with the turbine side of the system, as it is dealing with the hot gases expelled from the combustion chambers. The "cold side" refers to the compressor system, which (ideally) is drawing in cooler, fresh air from the engine compartment. I say ‘ideally’ because the air is being compressed, it heats up too… more on that later.
After that basic explanation, we can now move on to examining what goes into selecting a turbo system for a Fox Body Mustang.
Selecting a Fox Body Turbocharger
As explained above, the concept behind the workings of a turbocharger are pretty simple. However, carrying that concept into the physical is actually quite challenging and poses a lot of engineering challenges. Turbo systems are expensive – not because of the actual materials used (although some of it is pricey) but because of the thought process involved in getting a system to fit - there is a lot of fabrication and packaging engineering involved. Recall that turbo systems use a lot of piping, and all this piping has to twist and contour around all the other engine parts.
Aftermarket Turbo Kits For Fox Mustangs
Regarding ease of use, install and overall quality, in the Foxbody Mustang world there is but one company that gets it all right. Hellion turbo systems are a very high quality kit and have been engineered to retain all factory accessories. Another area of concern to look at when selecting a turbo kit is piping and weld quality. Because of the additional pressures and temperatures of the air, cheap piping and imperfect welds will show up right away under boost, often resulting in cracked pipes.
Turbocharger Waste Gates
Another indication of a quality kit is one that includes a waste gate. A waste gate (another turbo specific term) is a device that bleeds off pressure when the turbo reaches maximum rotational velocity. As engine RPM goes up, more exhaust gas is pushed out and the turbo will spin faster. However, all turbos do have a maximum RPM that when exceeded can cause catastrophic failure, usually in the form of exploding vanes. The job of the waste gate is to divert exhaust gases from the turbine when the turbo has reached its maximum speed, thus minimizing the chance of an explosion due to overspeed (for reference, many turbos spin at around 150 000 RPM).
Turbo Sizing For Different Mustangs
Another confusing matter to content with is turbo sizing. There are so many terms and variables involved with different turbos. To name a few, there is of course impeller size, housing size, A/R ratio, trim etc. To explain each and every variable would take pages of other technical terms and for that reason is beyond the scope of this article. However, it doesn’t mean there isn’t any advice to give.
A common mistake when picking a turbo for your particular Mustang is to think in terms of boost. Sure, different turbos can produce different amounts of boost, but that isn’t the be-all-end-all concept that many think it is. When selecting a turbo kit, think instead in terms of horsepower. What are your power goals? Once you settle on a power goal, for street or weekend warriors, pick the smallest turbo that will allow you to meet your goal. Selecting a turbo with this method guarantees the best possible turbo spool time, which means reaching maximum boost in less time and ensures best possible street manners.
Turbocharger Supporting Modifications
Unfortunately, a turbo is one of those modifications that require other modifications to really maximize its potential. First and foremost, fuel system upgrades are in order if they haven’t already been done. Larger injectors and a higher capacity fuel pump (maybe even two) are needed to be able to use all that extra air a turbo is pumping in. Secondly, the extra pressure can easily lift a head or blow a head gasket or even both when using the stock head bolts. Converting to a stronger stud setup is highly recommended. Finally, there is the issue of computer tuning. It is highly recommended to get an aftermarket tune on your Fox when running a turbo. Compressing the air increases the temperature of the air, which makes the combustion mixture more prone to detonation. An aftermarket tune ensures that the fuel is being delivered both in the right amount and right time. At a very minimum, retarding the engine timing is needed. Running with a lower compression is advised as well.
Fox Body Interoolers
A method to combat these increased temperatures (and can also increase power levels) is to use an intercooler. An intercooler is basically a mini radiator that is plumbed into the cold side of the turbo such that the intake charge is run through the intercooler prior entering the cylinder head. Not all kits include these, so double check beforehand (the Hellion does, another reason why it is one of the best kits out there).
To Turbo or Not to Turbo Your Fox Body Mustang
At the end of the day, turbo systems are an expensive modification. However, when using a quality kit, the extra couple of hundred horsepower that comes with it is usually enough to make you forget. Again, be wary of cheaper or knock off versions out there. Not to say that they don’t work, but rather include fitment and quality issues. Spending a little more upfront will save a lot of headaches later down the road.