This engine (3g Eclipse version with variable induction manifold) is a 2997cc (3 liter) SOHC V6 with a 10.1 compression ratio, and an iron block with an aluminum head.
It comes with 210 hp @5750rpm and 205 lb-ft of torque @3750rpm from the factory. This motor out of the box, emphasizes reliability and low to mid-range power, giving decent torque throughout the power band.
In the 3rd Generation Eclipse it can be found in two forms, Fed spec and Cali Spec. Usually, Eclipses from the Year 2000 are fed spec, while the others are all Cali spec, the biggest difference between the two is that the Cali spec has 2 pre-cats coming from exhaust manifold before going to the main cat. This was done to achieve better emissions, even though it restricts exhaust flow.
This engine is much more capable performance-wise than it has been given credit for. It is often said that this engine cannot take more than 10 lbs of boost from a supercharger or turbocharger (which is sufficient to make MORE than enough power than is needed to have fun in a fwd car). This is not true-every engine is different, every engine has its weaknesses and strenths and the 6G72 is no different.
Rather than turbocharging the 6G72, owners have found that supercharging is the best way to go for performance since it is not that the engine has a hard time handling power, but rather the extreme heat generated by a turbocharger instead.
If a turbocharger is the desired route for performance, the 6G72 can be turbocharged by using a kit pieced together, as no kits currently exist. The most often used turbocharger is a T3/T4 hybrid, for quick spool-up and decent power at moderate boost levels. For supercharging, the RIPP supercharger kit, using a Vortech supercharger is available in several stages, and while more expensive is the preferred method of pumping up this motor with the stage 1 kit producing 295 hp from the motor with only 5-6 lbs of boost.
If you are daring enough, Nitrous Oxide may also be used with the stock motor being able to handle a 50hp shot and possibly more, though not recommended with stock internals.
For the average driver seeking to enhance the engine and produce good power without breaking their wallet (or their car), this is my personal recommendation for performance.
Stage 1: AEM Short Ram Intake/GReddy Evo2 Catback Exhaust:
I would choose the short ram based on the fact that this engine already emphasizes off the line power and the short ram allows the air to reach the MAF sensor faster, and are also known for bottom end power. With these two modifications, you can expect a gain of about 9hp and about the same amount of torque to the wheels, a much enhanced powerband, and an awesome sound of the intake/exhaust combo.
These two modifications will increase volumetric efficiency of your engine, or in other words, allow to the engine to "breathe better"
Stage 2: If you want more performance, then I would recommend headers and an ECU reflash or APEXi Super Airlow Computer (S-AFC). Headers will allow you to rid yourself of the pre-cats and gains of up to 20hp and 14ft- lbs of torque at the wheels have been achieved with CMF Short Tube Headers. Other options that I would recommend would be headers from RPW which are cheaper and of good quality, but are made from mild steel (which can be painted with high-temp paint) instead of CMF's stainless steel.
The ECU flash or S-AFC will allow you to remap your engines air/fuel map and allow you to make minor tweaks to your power band. With basic mods, around 8-15hp can be gained from working with your ecu. Unless you prefer to spend great amounts of money on a full standalone unit like AEM's, these are your best bets for ECU tuning.
Stage 3: At this point I would recommend possibly porting your throttle body to 65mm and/or manifold (another option is to switch out the manifold from the Diamante, another Mitsu car with a similar engine). The manifold is not the biggest priority for the later versions (03-05) of the 6G72 motor found in the Eclipse GTS or Spyder GT/GTS because the Variable induction manifold that came with it is very well constructed and aids in performance decently as it sits.
If you choose to swap your manifold/throttle body you will lose your cruise control as it removes certain sensors that control it.
You may also consider (if you choose to continue modifying at this point)to purchase a mild set of camshafts from a company such as RPW, along with other extranneous mods such as spark plugs, wires, grounding kit,which are cheap, but these will not do much for you unless your engine needs them or is fairly modified.
For more information you can go to tearstone.com, club3g.com, or eclipseforums.org. If you go to the latter just look for or pm the user OZZYGT.