Feel free to check it out and hit me back here with questions/comments. My use-case for this was my FiST and a V8 audi; I have not tested extensively with every car/exhaust combination, so I am not sure how something like a v8 with true duals and an x-pipe would be calculated (pulses per rpm -> frequency), but if you get the frequency via a spectrum analyzer the rest of the sheet works fine. Please copy the calculator to your own google drive and use it that way. As it always needs to be said, I am not responsible for your use of this tool, it's just the reference I have been using for myself and as there are a ton of environmental variables you need to pay close attention when utilizing it.
https://docs.google.com/spreadsheets/d/1lDwwrAibQa-cqZWlNG-Y04wATCq5bGZLWIsL7phyHBo/edit?usp=sharing
https://docs.google.com/spreadsheets/d/1lDwwrAibQa-cqZWlNG-Y04wATCq5bGZLWIsL7phyHBo/edit?usp=sharing