you should come over to 190revolution.net and post this question. I will tell you right off the bat that the Jet chip is a waste of money. We have electromechanical fuel injection and an equally old school coil pack ignition system. There is not anything that you can do to the CIS-E module to pull more power from the engine. You COULD tweat the fuel metering system, but that would be pretty useless IMHO and would likely cause more problems than it is worth in the long run. Piggyback ECU chips work on newer generations of cars with fully electronic engine controls, but you will be out of luck in any w201.

Headers are worth it, especially on the 2.3 8v motors. The exhuast will likely end up being more of an aesthetic improvement (sound, appearance) rather than a performance gain. To be honest there aren't too many things that you can do to these engines on a "budget". You could definitely get results w/ 5-10k USD in engine building work, but there are no "bolt-ons" per se that will yield anything. An m104 24v I6 swap is probably your best bet at this point if you have 5k bones to spend. It has been done by a good number of folks over on the 190 site, and there are at least a couple that did enough of it themselves that they could probably help you. One was a m104 from a C36 AMG which would probably be just about the ultimate 190e, even in 268 HP (MY 1995) form.

Nothing comes cheaply here sadly

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1999 C43 AMG ~~~ 744 on black, mostly stock
1991 190e 2.6 ~~~ m117 5.6 project car