I've been thinking about the display. I briefly looked at the Nokia LCD shields for the Arduino, but have so far dismissed them. I've also looked at the larger monochrome displays available, and similar dismissed them.The Nokia displays, while color are too small (128x128 pixels and about 2.5" square), where the large ones are fine, they only are monochrome.
There is a bunch of information one can encode in a color display, everything from warnings, to dithering edges to allow more data on less screen. I am sure I could, if so motivated, put enough information on one small color display. Connecting multiple of these smaller displays up to a network from the main board is another option, maybe allowing 2-1/4" holes to display analog looking gauges. It would certainly be an option.
Using a larger monochome display could work, and for many years there was the popular VM-1000 display that was monochrome. Alerts could be encoded as blinking or changing presentation, including reverse video. The display can show analog and digital presentations, allowing quick checks for out of tolerance readings, and a longer view of specific readings.
Combining displays, making a comprehensive view will allow quick scans to determine more information. Combining all oil and temp into a single graph would allow noting any issues with the oiling system. A similar display could show CHT's and EGT's allowing quick viewing of current cooling status. The comprehensive display will allow showing more data in a larger color display.
Using direct connected displays would also have the disadvantage of requiring something to be farther from the engine. The display being close to the pilot would need to have all the sensor wires brought forward, where mounting the display and engine monitor near the engine would require the pilot to turn around to read the display. (We are talking a Cozy here, not a Cessna, but something similar to an Osprey II or non-traditional engine mounting would be covered).
I am planning on using an Android device for a display. The Android can receive the Arduino data over bluetooth, and possibly USB. Currently tablets are available for about $150 on up, or if you have an Android phone, it should work without any additional expense.The Android has a robust open development platform, and the tools are mostly open.
Using bluetooth allows the option of connecting to other devices, including full laptops, ipads, and other brand computers. I am not going to work on them, but all others to do it if they desire. This is an open project, read and learn along with me.