That’s my point. It’s a little different when you don’t have a proven OEM tune to build off of when changing compression, displacement, head flow, cam, rocker ratio, injectors, MAF, etc. You have to use gross calculations and best guesses… or you just have tons of experience.
I would consider changing the timing and fuel on a stock internal motor to “tweaking” a factory tune, not very much is changed in this case. Anyone can tweak with a little research and basic knowledge of safe limits and a wideband o2 sensor.
If you need to get an idea of what is changed in a cammed LS1 to get it to idle and run correctly I can show you my HP tuners calibration. You can open any tune regardless of license, and you can even use the compare feature. Compare my calibration to a factory 1999 calibration and your head will spin.
That being said, I am an amateur tuner by most standards. I have tuned with HP tuners for 5 years, CROME for 4 years and FlashPro for less than a year. I only street tune, and since my car is a daily driver it doesn’t afford me any downtime.