• Oil temperature: greater than 270F
• Oil pressure: less than 10psi
• Coolant temperature: greater than 200F
• Boost: greater than 10psi
• Air fuel ratio: greater than 15:1 for normal, greater than 14:1 for boosted
• Volts: greater than 15v or less than 10v

Some of the major parts I used:

• PICAxe 40 brain. I buy mine (and other PICAxe related stuff) from Peter Anderson. Folks in the UK can buy them almost anywhere. I haven't talked to Peter in a while and I don't know if he still sells so ask him first!
• Any standard serial LCD character display (cheapest I could find was 411 Technology Systems). See notes below on interfacing with parallel LCDs.
• LM34 digital temperature sensor for temperatures (reads from -50 to 300 F, which is enough range for all liquids and gasses in your car)
• DS1307 I2C Real-Time Clock was used as the cockpit timer or can be used to display the current time if you like
• Scheme for the power supply that I used is here

Other thoughts (use Google for more info, or email me):

• Use a "voltage divider" to reduce the car's voltage to a measurable input level
• PICAxe to LCD interfacing, the hard way
• PICAxe to LCD interfacing, the easy way . Note that I used the LCD108 that he no longer sells. If you use my pinouts this might be different!
• A digital compass that could work (I2C) is the Devantech CMPS03, or the HM55B
• An easy DIY Air-Fuel meter can be found here
• I tapped into the Miata's heater core send hose for water temperature readings
• I drilled a hole in my oil drain plug and epoxied the temperature sensor in the hole using JB Weld. Two years later and no leaks!
• A partial pinout of the circuit in my car is here
• The last time I looked www.turbofreak.com had some good info on air pressure sensors for you boosted folks.
• The air to fuel ratio section is temperamental because you are measuring a very small voltage difference. The more stable you can make the signal and the power supply the better luck you'll have with that.
• I found that the engine bay of a car is HORRIBLY noisy in terms of electrical interference. Follow all the instructions on the LM34 datasheet for long distance readings and noise suppression and check out Peter's suggestions for more ideas on long distance noise suppression.

PICAxe source code:
This code works, but could definitely be improved upon. There are great PICAxe forums on the internet, as well as electronics forums for hobbyists.

normalyaspirated.bas

Good luck and let me know if you have any questions or if you have any success. I'm always excited to hear about other people's projects that I have helped inspire!