I talked with The Boy about the project and here's his take.
Pi + GPS + accelerometer = piece of cake. He said he could probably have it built and ready for trial runs in about a day. A weekend at the most. Still, not going to happen until this semester is over. He's up to his eyeballs in class assignments and working as a tutor.
He's making A's and B's and earning some spending money, so I'm cool with that.
Adding data input from the tach is a little more complicated. We'd both need to do some research, but he's pretty sure the Pi would take it as is and is sure it would if we put the pulse through a voltage limiter / stabilizer circuit. $5. Programming is a few lines of code to covert frequency to rpm and dump data into an array.
Adding 3 EGT probes using K type thermocouples- Easy peasy. Similar to above
Adding a real time display - Now we're getting into a lot more programming work. He's done some already in school and already has a few gauge maps built, still a good bit of work.
We agreed that I'd take the next couple of months to research and learn. During that time we'd agree on the project scope and I'd have everything here when he comes home in May.
I AM SO LOOKING FORWARD TO THIS!!!!!
I get to spend some time building bridges with my Son. He doesn't realize it, but I'm getting a chance to recognize him as an adult, do something worthwhile, and give him affirmation. That's a lot of reward for a $150 investment.