You would run lean but as for how much depends on how much alcohol you are using. If you advanced timing with your tune then you would most likely see detonation and yes you could potentially damage your engine depending on how aggressive your tune is. If you have a very moderate tune then you would most likely be fine. Let me know if you want some good sources on alcohol injection to read up on the subject. It is a lot of fun to tune with and you can make really good power. I have a big case of 80% methanol/20% Nitromethane I had custom mixed sitting in my spare bedroom waiting to be used when I decide to install alcohol inj. on the srt6 You see some very nice gains running the nitromethane mix in there!