The theory about Twin TurboChargers vs. Single Turbo. There are certain facts and laws of nature that every diesel driver faces.  Among these are:

1. Ambient (atmosphere) air pressure is approx 14.7 psi at sea level, and around 4300 feet altitude, around 10 psi.
2. Turbochargers only function at their best in a limited band of RPM's.

When you combine these two facts together you come up with some interesting problems.  You have a few choices.  You can either choose a small turbo, which functions very well with your engine at low RPM's, but limits high end power.  You can get a large turbo which functions good at wide open throttle (WOT), but is horrible to just drive around town because it won't spool up (spool up refers to the amount of time it takes for the turbo to begin to produce boost).  Or you can choose a medium sized turbo which spool's up relatively well, and at WOT still has some exhaust restriction but allows a lot more power and cooler EGT's than the small turbo.  Yep, that's what your stuck with when you're choosing a single turbo.  Sure there are much better choices than others, for example our D-Tech Turbocharger, which offers a huge increase in airflow and performance than the stock turbo, as well as has amazing spool up.  But ultimately a single charger does have the restrictions listed above.

Part of the big problem is the ambient (atmospheric) air pressure, we mentioned earlier.  If the boost pressure on your truck shows 35 psi, this is actually the gage pressure, or (psig), which means the zero on the gage is actually 10 psi (at 4,300 feet altitude) or atmospheric pressure.  The actual pressure is 10psi + 35psi = 45psi, or actual pressure (psia).  What this means is that the pressure trying to get into the turbo is only 10 psi, and despite how fast you spin the turbo, there is only 10 psi pushing air in, and if you spin the turbo too fast it becomes inefficient at bringing new air in, while it becomes increasingly harder to get exhaust out.  To overcome this with a single turbo, people increase the sizes of turbines, housings, compressors, on and on, and may increase the amount of airflow, but ultimately hurt low end drivability and spool up, and all because they are up against those pesky laws of physics.  A certain size of hole (the turbo air inlet) will only flow a limited amount of air at a given pressure. Atmospheric pressure becomes a huge limiting factor.

So what's the solution...Twins (turbos that is) also known as compound turbos, actually two turbos placed sequentially (one flowing into the other).  But not just any two turbos will work together, they must be sized correctly to complement each other or they can fight each other and not work properly.  These two turbos will consist of a smaller charger, and a largeer charger.  The small turbo is the first to get exhaust from the engine, and the last turbo to touch the fresh air.  Fresh air enters a large (slower spooling) turbo first is pressurized, and then fed into the small (quick spooling) turbo, which then multiplies the already pressurized air, and then feeds the air into the engine.

The beauty of the whole staged, two turbo concept is this.  First of all you can have all of the benefits from a small quick spooling turbocharger, with more-than-all of the benefits of a very large turbocharger.

Turbos multiply atmospheric pressure, not add it, but function by multiplying it.  Therefore if the small turbo as a single can take air at 10 psi, and produce 40 psi boost, it is multiplying the air by 4 times (10psi x 4 = 40psi).  The large turbo can do a similar job.  Therefore let's say that the large turbo multiplies by 2.5 times, it takes 10psi (atmospheric pressure, where we are located at 4300 feet above sea level) and makes 25psi. (not taking into account abiatic efficiencies), now the small turbo will see 25 psi at it's air inlet, but it think it's only seeing atmospheric pressure, or literally over double the amount that atmospheric would allow.  So we can literally cram over double the volume of air into the same inlet hole size in the small turbo.  So if the small turbo then multiplies the air by 4 times you'll see 25psi x 4 = 100psi.  But just so we really let the engine breathe and don't create more boost than necessary, we allow the small turbo to wastegate early so that the 25 psi made by the large turbo is only multiplied by say 2.25 times to give us 56.25 psi of boost (25 x 2.25 = 56.25).  This makes the small turbo spin much slower, an in doing so increases the pumping efficiency, and stress on the turbo.  But don't forget that in allowing the small turbo to wastegate early, the exhaust (drive) pressure goes way down.  To show the increase in compressing efficiency, our Twin Turbo Kit at 60 psi of boost produces compressed air temps (before the intercooler) of appx. 375 degrees F, while at 35 pis the stock turbo produces air temps of appx. 465 degrees F.  the results are cooler inlet air, more inlet air, and a much cooler running, more powerful engine.

So in a single turbo application, at 35psi boost we would typically see the exhaust (drive) pressure at around 55-65 psi.  While on our Twin Turbo Kit at 55-60psi boost, the exhaust (drive) pressure is around 45-50psi.  So exhaust pressure drops by 10-20psi, while boost pressure is 55-60psi, this is 157% more air going into the engine, while allowing the exhaust to escape 30% easier.  On our properly engineered Twin Turbo Kit, all of these details translates into much more horsepower, much lower EGT's, better fuel mileage, a much broader RPM range (quick spool up, with huge high end WOT potential), and overall a much more drivable, high performance truck.

So next time you see one a manufacturer trying to sell a single turbo, saying that it will compete with our Twin Turbos, ask yourself, if the laws of physics don't allow it, how are they claiming it.

Our customers all say that once they have installed our Twin Turbo Kit, they could never go back to a single turbo.