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So is it possible to crank out 400+ hp out of the A5 3.0TDI?

What would have to be done in order to accomplish such a power output?

The car is great in every way. But I am sort of a power freak and wouldn't mind another 100 or so hp. :)

Currently have a tuning chip, that I am not sure does anything at all to the car. (If someone here in Sweden have an A5 with the MTM kit, let me know! I wanna meet up and compare!).

I wonder why diesels aren't made with 400-500hp. Is it due to the problem handling the torque?
Coming from a Supra background where it's easy to end up at 400rwhp even by accident (whoops, this exhaust flows too much), I can say that all you need are a few main things to secure 400 bhp (which in an AWD setup equates to maybe 320 whp):

- gotta make sure the motor can take the boost without blowing up. common weak points are the head gasket, piston rings, and anything that may be prone to damage by overheating (aluminum blocks/heads warp very easily compared to cast iron, etc) which brings me to the next point:
- gotta make sure the cooling system can keep up. more boost equals more heat, and more heat equals more wear. this includes cooling the engine oil as well, since if the oil operates outside of its optimal range, it can break down or not lubricate optimally, and can cause engine damage. you may need to run a different viscosity than factory.
- the turbo(s) need to flow enough. once you exceed the efficient flow rate of a given turbocharger, it starts producing a lot more heat, which not only works against point number 2, but also reduces the amount of power you gain by it pushing additional air
- have to make sure the intercooler is still in its efficient range. since we've established that more boost equals more heat, you need to cool that intake charge back down in order to make efficient power out of it (since cooler air has denser molecules which in turn produces more combustion)... this will also aid in #2
- make sure the fuel system can deliver enough fuel to keep the mixture from pre-igniting. I'm not a seasoned diesel expert, but I'm aware that the motor can handle pinging a lot more than a petrol motor since its ignition system is based on pinging rather than on spark plugs -- however in ANY motor, pre-ignition is still very bad (causes stress on pistons ad rods). The fuel enrichment on turbo cars also serves to cool the pistons down. Common weak points are the fuel pump, fuel pressure regulator, and injectors (not sure what the diesel equivalent is here).
- make sure the ECU is mapped to handle the amount of boost it is going to see. In most modern boosted applications, the majority of the ECU's ignition and fuel mixture based decisions are made based on what it sees coming from a combination of the MAP (manifold absolute pressure) sensor and MAF (mass air flow) sensor. If the amount of boost you are running exceeds what the ECU has mapped out, it will either cut the ignition (sometimes referred to as a 'fuel cut') or it will just run lean and you'll blow up your motor
- make sure the drivetrain can handle it. Diesel drivetrains are built to handle gobs of torque, but you'll never know where the limit is until you break something. The common weak point will be the clutch disc and pressure plate, which were designed for maximum comfort at factory power levels. You may need to upgrade to a stronger clutch kit

That's all I can think of for now, but basically you need ALL of these things covered before pushing the boundaries. Also know that the more you push beyond the factory power level, the more volatile the whole thing becomes. Completely stock, you can just put in the key and drive, but with more boost, you need to pay a lot more attention to varying outside temperatures, exhaust temperatures, the effects of heat soak, the effects of crappy gas, and an overall hit on reliability. This is why a lot of big boost projects end up with a large array of gauges on the dash to monitor every little thing to make sure all is well.

My personal opinion is that it can be fun, educational, and rewarding, but I wouldn't do this on a car that I depended on to take me to work.
 
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