Automotive advice. ardunio based gauge unit.

Hi guys,

New to this forum for the last three-six months i have been looking into digital gauge units for my race car. having built most of the car myself. im coming up to the electronic side of things this is no massive job well it is but i have help from my father. a qualified elect. Now he has put me onto the arduino and i have spent the last two-three weeks talking them up with the girl friend about the things they can do.

My goal is to make a basic Digital screen read out to show

Tacho
Speed
Fuel

Now this is not that hard. i have seen heaps of write ups on how to do these. it got me thinking into What i would LOVE out of a gauge unit. and i was thinking about

GPS lap timer and Knock read out. Im running a aftermarket ECU in my car (autronic) so i dont have ODB2 but i do have a head phone jack out to serial cable. now this will help me get a tacho reading and knock. if i can figure out what info is coming out from the cable. (currently trying to get info out from the company)

i was thinking since i have different gear ratios to stock my normal speed sensor is pointless. so i should run a GPS one. i guess where im at is. the unit i was going to buy a Greddy E01 done all the above other then lap timer/GPS speedo (normal speedo) but Greddy no longer support this and i cant work out the firmware to remove the boost side of things show i can show my 4 items on the screen at once. (they only allow three of there 4 inputs to be displayed at a time)

So here is where im at. im happy to put in the work to get what im after and i want to do things right the 1st time. Should i sell off all my other gauges and just buy a race dash and cut my losses? should i try and crack this firmware? should i try and work out this aftermarket ECU output? should i hardwire stuff to the Arduino?

Is there anything i should look at adding? it is a race only car i got gauges for just about everything else but these items.

Sorry if i have gone all over the place just trying to work out what i want and how to go about it? i have a arduino sitting next to me i got all the emulators and bread board stuff to give it a go.