MeqaSquirt is a new Engine Managament Computer. I'm thinking its standalone (non piggy Back). If you're wanting to do something like this swap i'd go with a Haltech E6k. But then again i'm running an APEXi Power Fc Full stand alone in my Rx7. I shoulda got the Haltech. Hope this helps.
A. MegaSquirt is an experimental Do-It-Yourself programmable electronic fuel injection controller that will work on virtually any liquid fueled spark-ignition engine. Note that MegaSquirt is the controller only, you will have to gather the remaining fuel system parts yourself (from 1 to 16 injectors, sensors, fuel rails, fuel pump, etc.).
Experimental means that YOU are responsible for sorting out some details of your fuel injection that are specific to your application. Do-it-yourself means that you save money by assembling it yourself with a few basic tools and comprehensive instructions.
MegaSquirt will work on one to 16 or more injectors, of high or low impedance, and for any number of cylinders, even three and five cylinder engines and odd-fire engines.