I am prepping a car for competition in the Chumpcar series and am swapping over to Grand Am brakes on all 4 corners of my 87 GT. I am looking to upgrade the master cylinder next and have seen 2 options. Either the 1994 Full Size Blazer M/C or the 1993 S10 Blazer M/C. My understanding is the the Full Size M/C will make the pedal firmer and the S10 M/C would be more like stock. This will be a race car only, which M/C would be the better fit for my application?

I used the S-10 Blazer M/C on my 86 SE and am very pleased.

Read this:
http://dev.stoptech.com/doc...dualmaster-guide.pdf

A larger master cylinder will provide reduced line pressure for the same given pedal force, but will provide greater volume displacement per unit of pedal travel.
Comparing bore sizes will provide you with a relative difference in performance. How you feel it should be is up to you though, of course you need enough fluid to displace the distance the calipers will travel in one pump of the master cylinder.