I've done a lot of searching the past few days and I've come up with some conflicting information.

I want to swap out my stock master cylinder and (hopefully) retain the stock booster on my EM1. What exactly are the 1" options? Are GSR MC 1" Prelude? If so what years? And do any or all of these bolt on the stock booster with out modifying the brake hardline orientation?

 

What is the reasoning behind you wanting to go up in size on the master cylinder? Did you upgrade your rotors/calipers?

 

Grassroots motorsports had an interesting article a few months ago about why a bigger master cylinder is bad. They basically explained how it impacts brake balance and shouldn't be done unless your brakes have changed (such as big brakes on the front, etc.)