Originally Posted by manitou
If you have good pump gas and you'll mostly be using E85 then I would consider the 9:1 CR. Our D25 heads (from the EJ255) do seem to work well with the high CR. I love my off boost response with the higher compression. I was driving around a bit today on pump and mostly out of boost, the gauge said 11 psi max but the car is peppy even at lower boost and it's amazing how usable 3rd gear is at lower speeds!
I also was very happy with my higher compression results. I was running just shy of 9.8:1CR on my bugeye with D25 heads, and it was extremely responsive in daily driving situations. It felt almost NA in off boost situations, and the best part about all of it was the mpg I was seeing on my high compression motor vs. my standard compression motor. I was seeing 2 mpg better across the board with the higher CR engine. I don't necessarily believe the higher compression actually achieved better fuel efficiency, but more that it made more wtq off boost vs the lower CR setup of the previous engine, which allowed me to not need as much go pedal to get the same "butt dyno" feeling around town.