WABJ11 said:
The Wizard of Odds has a nice section dedicated to card removal in BJ and its effect on the odds.
But I'm interested if someone knows, or has a link to the effect of additional cards added.
There's a way to experiment for an answer.
Go to my website program
http://www.bjstrat.net/cgi-bin/cdca_web.exe
Input some number of decks greater than 1 and remove some ranks but not others.
For example I computed the effect of adding 4 fives to a single deck by inputting 2 decks and removing 4 (2,3,4,6,7,8,9,A) and 16 tens. The resulting composition is 4,4,4,8,4,4,4,4,16,4 (2-A). This is a single deck with 4 fives added. When 'Compute' is clicked with nothing else input the overall EV for this composition and default rules for the program is computed. Using best strategy the EV for adding 4 fives to a single deck is -2.539% as compared to a standard full single deck EV using best strategy = +.0248%.
The range of decks you can input is 1 to 41,297,762 so you can do a lot of experimenting.

There's a Help link to explain basically how the program works.