Cm570 vs 870

[John Doe]

This has probably been discussed before but I tried finding it in the search bar and was unsuccessful. Please attach the thread and I’ll go about my day if you can help me out.

I want to know which of these earlier motors was the best at fuel efficiency and if there is a tune or upgrade I can make to get something close to the fuel efficiency of the newest isx engines.

I am an aspiring hyper miler and I can squeeze 8 mpg out of my 2350 if i try my best. However i recently discovered the cost of down time on my business and it was a very bad time for me. It was emissions related just a really bad experience at rush truck centers in Tulsa OK. And it got me thinking that if I had the consistent emissions problems my friends are getting i would surely be out of business. I literally lose sleep over this. And I do everything I can to keep the emissions running right.
That’s why I’m looking into these older motors, i don’t want to have to worry about the weeks of down time trying to fix the problems and I’m willing to sacrifice some fuel efficiency because there’s no way that the lower mpg will offset the cost of profit lost to emissions shop time.