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Some of us enjoy being able to hack our cars.

it would be nice if I could just hook up a PC and configure the factory ECU.

Man, subarus have been so unbelievably hacked it is awesome.

Cobb Tuning has a product that lets you flash your factory ECU with whatever you want. I use their (possibly) defunct product "StreetTuner" which is basically the same thing except in real-time... All through the ODBII port

no plug wires either, i'm afraid. the coils sit ontop of the spark plugs. Cobb's Accessport has a theft deterrent map which either cripples or disables the engine until the map gets switched. it's a PIA to switch the map each time you park though. Also, you'd need to carry around the accessport to swap maps - inconvienient at best. Better off with good theft insurance.

To follow up a bit more on the parent, for the WRX there are a number of options out there for "rechipping".

One thing to keep in mind is that modern ECUs like the one in the WRX are quite advanced and are able to adjust for many things like fuel octane, temperature, altitude, etc, while trying to maintain maximum performance. However, very often they leave some performance on the table to leave a greater safety of margin. Generally, the number 1 enemy of an engine (especially a turbo charged engine) is detonation. Followed closely by that is running too rich. Detonation will physically break an engine by either cracking pistons and/or rings or flattening rod/crank bearings causing oil starvation and thrown rods. Running too rich allows too much fuel to wash by the cylinder rings which gets into the oil and fuel is a horrible lubricant. Too much fuel leads to high metal wear and eventually bearing failure and thrown rods. If you avoid these issues, modest power gains are available.

One method is to reprogram the ECU or reflash it. A couple of companies (ECUTEK and Cobb Tuning) have reverse engineered the ECU in the WRX so that they can reprogram it.

Another method is to plug in a piggy back ECU (TurboXS UTEC) which alters the stock ECU's outputs as the tuner desires.

One drawback is that with a piggy back unit overriding the ECU's control, you lose a lot of the nice safety features of the stock ECU like being able to adjust for current running conditions unless the piggy back unit implements those adjustments itself. The other drawback is that sometimes the ECU will say "WTF, the car isn't doing what I'm telling it to" and switch into limp mode thinking that something is drastically wrong.

Finally, another method is to completely replace the stock ECU with a unit designed to be programmable. A few examples of companies which make this is Link and Electromotive. The drawback of a replacement ECU is that often, they do not have all the features of the stock ECU which generally means that it's a lot more work to get a good initial tune, and there's a lot more work required to swap out your stock controls with the replacement.

Most tuners for the WRX have found that they are able to get another 25hp or so out of the stock engine (227hp) without significantly affecting engine reliability by slightly adjusting fuel, timing and boost levels. However, once you start doing further modifications (like replacing stock cats with high-flow units or more efficient intercoolers) you will be able to further tune the engine to take advantage advantage of the engine's improved breathability and detonation resistance. With a setup like that you can get another 25hp without any significant reduction in reliability assuming that the tuning was done properly.

They can overlap in major ways. The best way to get more power out of your car (without adding a turbo or supercharger) is to remap your car's fuel and timing (and boost, if you've got a turbo already) curves in the ECU. The code is proprietary to each manufacturer, so you have to reverse-engineer it first.

I own a Subaru Impreza WRX, and one of the major tuning companies, Cobb Tuning, hired a computer engineer to do exactly that. Now I can pay $400 for 35 more horsepower. I like the crossover.

Ok, if you're going to get technical...

Z06 = ~$45000 USD
WRX = ~$23000 USD

Now let's spend the $22K difference to make it even...

Well for <$5K we could take it up to 368HP with this stage 4 kit. Lets say it takes 15 hours for a professional installation at $100/hour then that takes us up another $1500 bringing us to a total of $29500.

Now let's smack on a Stage 3 short block for more reliability. That's another $6700 including labor. That takes us up to $36200.

Even though the AWD will easily make up the difference of HP vs. RWD (unless we're driving on a nice hot track) lets spend $2k more on a nitrous kit just to make sure we can embarass the Z06.
That only takes us up to $38200.

$4000 for a stage 3 suspension kit. Taking us to $42000.

Wheels: 4 17x7.5 Prodrive GC-06D $1,900
Tires: 4 225/45YR17 BFGoodrich g-Force T/A KD $780

That will take us up to ~$45000. For a machine that will embarass pretty much anything else in that price range. You could argue the reliability of the WRX, but when you're comparing it with an American car is that really relevant?

Personally I'd rather just spend $12K on a Hayabusa (yes it is a motorcycle, yes it ONLY has a 4cyl engine) and embarass them both.

Ok, if you're going to get technical...

Z06 = ~$45000 USD
WRX = ~$23000 USD

Now let's spend the $22K difference to make it even...

Well for <$5K we could take it up to 368HP with this stage 4 kit. Lets say it takes 15 hours for a professional installation at $100/hour then that takes us up another $1500 bringing us to a total of $29500.

Now let's smack on a Stage 3 short block for more reliability. That's another $6700 including labor. That takes us up to $36200.

Even though the AWD will easily make up the difference of HP vs. RWD (unless we're driving on a nice hot track) lets spend $2k more on a nitrous kit just to make sure we can embarass the Z06.
That only takes us up to $38200.

$4000 for a stage 3 suspension kit. Taking us to $42000.

Wheels: 4 17x7.5 Prodrive GC-06D $1,900
Tires: 4 225/45YR17 BFGoodrich g-Force T/A KD $780

That will take us up to ~$45000. For a machine that will embarass pretty much anything else in that price range. You could argue the reliability of the WRX, but when you're comparing it with an American car is that really relevant?

Personally I'd rather just spend $12K on a Hayabusa (yes it is a motorcycle, yes it ONLY has a 4cyl engine) and embarass them both.

For those with Subarus and not VW's.. Cobb Tuning has done similar work with Subarus. A lot of the tuning (but most definitely not all) that is done on turbocharged and supercharged cars nowadays is through software, making sure you're making best use of the fuel used - different programs for different octane levels.