switching from e85 to e75? how much boost is safe
 

Since I purchased my car last year, I have been cocktailing e 98 w e75 to get e 85. It is a total pain in the ass considering the e98 is an hr away. And I dont really want a 55 gal drum at my house. I do have a pump 2 miles from home w e85 but it is 75% in summer and 70% in winter. So it would make my life much easier and cheaper to just tune on e 75. The high boost setting on my car is at 21 psi.normally just drive at 15 psi. How much boost can I run safely. Do I need to back off timing a little? I am becoming more familiar w my microtech. Have been doing some street tuning on on
pump gas to cruize around on in winter. Should I just put on dyno on my e85 map and subtract fuel w e75. Thanks for any input.
John

Also car has pre turbo water injection at 15 psi

Is there a big difference in the alcohol cooling effects from 75 to 85%.

Does your Microtech support Flexfuel? Having a good ECU with Flexfuel capabilities would make your life way easier.

Unfortunately no it is old microtech lt10s.