Stock 2.2l I-4.
There's not a lot available for the Probe's transmission, but I've done what I could. I threw in an adjustable-height Pace Setter short-shifter and that really firmed things up. It gives really tight, quick shifts.
Here you can see the armor coated Pace Setter headers, Nology Hotwires, RS Akimoto cone filter, and front strut tower brace. You'll also notice that I've removed the AC compressor, condenser and all associated plumbing. This serves 3 purposes: 1) Took about 40 lb off the front end, 2) Relieved parasitic drag on the engine from the compressor, and 3) Made room for a future turbo and intercooler. The silver tube gives my car cooler air to breath while driving.