Dear Mightymouse,
Turbocharging is possible with any car. On the crossfire, the simplest method would be to use a twin-turbo setup. Here is the simplest way to turbocharge your Crossfire:
1. Determine how much horsepower you would like to make. 300? 400? 500? 600? 700? 800? 900? 1000?
2. Calculate the airflow required to support the horsepower you want based on the displacement and efficiency of the SOHC M112 engine. This can be estimated.
3. Calculate the amount of PSI that is required to generate that airflow using that turbo. If the PSI value is greater than around 6 or 7 psi, you may have to consider rebuilding the engine with forged pistons. I believe the Mercedes M112 engine has stock forged crankarms.
3. Buy two correctly sized turbochargers. A correctly sized turbocharger is one that fits the specifications you computed in steps 2 and 3.
4. Weld up two turbo manifolds and mount the turbochargers.
5. Weld up two downpipes to connect the turbochargers to the exhaust.
6. Weld on an O2 sensor bung upstream of the catalytic converter and install a Bosch or Honda wideband Lambda sensor.
7. Connect oil feeds to the oil inlets of the turbos and vertical oil drain lines from the turbos to the oil pan.
8. Install a correctly sized intercooler to flow the air you calculated in step 2. This is to prevent detonation and increase air density (power)
9. Connect air intakes with installed blow-off valves leading from the turbo outlets to the intercooler inlets. Connect the intercooler outlets to the air intake manifold on the M112 engine.
Easy right? You have now added the air necessary to provide the horsepower you computed in step 1.
You already have the spark. Now you must time the spark to prevent detonation and add MORE FUEL!! Both are important otherwise your engine will literally explode.
There are three ways to do this:
1. Rechip the ECU and install bigger injectors. Possible, but I doubt anyone will do this for your custom turbo setup. You can make huge power this way.
2. Use an AFC Hack and bigger injectors. This is probably the most reasonable alternative, but will require you to install a MAP sensor on your intake manifold. You can make huge power this way.
3. Use a rising-rate FMU. This is low cost and rather old school. This is the way your dad used to turbocharge his car. The problem with this method is that it is not recommended for turbocharging beyond 6 or 7 psi. It will limit your power!!! Also, you will not be able to make this as efficient as rechipping or AFC hack methods.
There you go. Your car is making magnum power. Now you have to ask yourself, do you feel lucky? Well do ya? Will your transmission and differential handle the power, or will they explode when you try to run 1000 hp through them? If you do it, let us know.
Based on my experience turbocharging hondas, assuming you have a shop, it will cost about $600/turbo, $300 for metal to make the manifolds and intake pipes, $150 for the intercooler, $600 for the electronics/injectors, $200 for the wideband and controller. That comes to just under $2500 for a do-it-yourself job.
Here is a very good guide for turbocharging a 4-cylinder honda engine. Everything in this guide can be "scaled" up for your M112 engine:
http://beesandgoats.com/boostfaq/g2icturbo.html