911split,

When tuners flash the ROM (normally, Read Only Memory, except when being flashed) in the Powertrain Control Unit (PCU, aka ECU, ECM, etc.), they are poking (writing) new values into the various tables that are contained in the ROM. These tables contain the values for ignition advance, fuel/air mixture, etc. for various loads, engine RPM and throttle position. Ideally, the values that are poked are determined on a dyno with your car and the specific equipment/mods on your engine. If the values for your car are not determined on a dyno, then assuming that your engine is stock, they poke values for a typical stock engine for your make and model. These values may or may not have been determined on a dyno. If they were not determined on a dyno, then the tuners use typical values based on similar engines. These values are probably "close enough", given that the tuner is somewhat conservative in the values that he is using. If you have made mods to your engine (headers, exhaust, larger injectors, forced induction, etc.) and the values are not determined with your car on a dyno, then the tuner will use typical values for comparable mods. Again, these values are probably close enough, given that the tuner is fairly conservative. The values used by different tuners will vary slightly depending on how conservative the tuner feels he should be. As with other components for your car, the cost depends on what the market will bear, given "brand appeal", the reputation of the tuner, etc.

The drawbacks, dangers and risk of damage to your car depend on the values that the tuner pokes into the tables. Potential damage could be caused by too lean air/fuel mixtures, ignition too far advanced, or (if the rev limit of the engine has been raised) over-revving the engine. However, most reputable tuners will use values that are conservative enough so that the likelihood of damage to your engine is very small. Doing something that is likely to damage your engine is not going to help the tuner stay in business, and most tuners are concerned about their reputations and are in business for the long haul.

A manufacturer cannot void your warranty because you had your PCU flashed by a tuner. However, if damage occurs to your engine, and if the manufacturer/dealer suspects that the damage may have been caused by alterations to the table values in the PCU, and if the manufacturer/dealer can “prove” that your PCU was altered, and if he can prove that the altered values were responsible for the damage, then he can refuse to pay for the damage. Although it is very unlikely that the dealer will try to peek (read) the table values in your PCU during normal maintenance or repairs, it is not true that he can’t do so. If you can poke ROM, you can peek ROM.

Regarding the benefits of altering your PCU, it just depends on how conservative the manufacturer was when he developed the initial values. Traditionally, MB is not all that conservative, so the amount of horsepower/torque increases that you get by altering your PCU may not be as great as with some other manufacturers. However, from what I have read from forum members who have altered their PCUs in the Crossfire, you can expect increased throttle response, some increase in horsepower/torque, smoother power curves, and slightly better fuel economy. It is not necessarily true that reliability and durability of the engine will be compromised. That depends more on how you drive and maintain the car.

And it is likely that DaimlerChrysler will eventually provide an upgraded PCU for the Crossfire. Mopar (Chrysler’s performance unit) offers upgraded PCUs for most of their other other makes and models, and (with the exception of the high performance racing PCU for the Viper) all of these upgraded PCUs are included in the manufacturer’s warranty.

I hope this helps.