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So I'm running cobb stage 2 right now with stock exhaust and the car feels great. I was just wondering, since its possible to run the stage 2 with the stock exhaust why is a turbo back needed? Or more specifically, is the only difference that I will see more power gains?
 

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Short answer is you will see power gains, improved low end torque, and better (subjective) sound.

Long answer below...

Think of how all of these systems interoperate. You need air, fuel and spark to combust (air/fuel ratio). A turbo pressurizes the air to make it more dense so you get more air into the engine. The engine control systems must then provide more fuel to accommodate the higher volume of air otherwise you would run lean (more air than fuel = detonation = bad). Ultimately, the byproduct of the combustion is exhaust. Some of this exhaust gets used to drive the turbo, the rest goes out through the cat to be cleaned and then out the muffler where noise is dampened and finally into our lungs :D

All of these systems have limits. By default (from the factory), most turbo cars run pretty rich (more fuel than air = wasted fuel = safe) and the turbos are kept well below their limits in order to improve reliability and gas mileage.

The first mod you do, ECU flash, is a big one because it is throwing the factory tune out the window and making all of the parts work harder. Thats huge and shows very big bang for the buck. Cobb gives an "off the shelf" map meaning that it is as generic as such a thing can be. To keep this as safe as possible, the Cobb maps are still pretty conservative (but *way* better than stock). This is why tuners can extract more power with a "custom tune" - because they are monitoring and testing and tuning your actual car under real world conditions (every car is different)

Beyond the first ECU flash/tune, you can start to explore other bottlenecks and limits. The exhaust system is restrictive just like it is on any stock car. Once you are making more boost with a more aggressive tune, a more efficient exhaust system, to get gasses out, and a more efficient intake, to get air in, will become useful.

Even without a tune, throwing on intake and exhaust will show gains as the ECU does what it can to learn/adjust to the new Air/Fuel ratio.

So that initial flash is a big jump from stock... Optimizing the air flow and then reflashing to accommodate is another nice jump from the last jump and a HUGE jump from stock (like 100HP at the wheels)

After that, you are pretty much done and need to start exploring different turbos which ultimately needs to needing more fuel, etc.

For sticklers, yes I realize the above is not scientifically perfect, but its good enough for govt work! :thumbup:
 
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