I used the following to allow logs larger than 100KB in CruiseControl.rb:

 # Number of times more logging than the default 
 MORE_LOGGING = 5

 Build.class_eval do

   def contents_for_display(file)
     return '' unless File.file?(file) && File.readable?(file)
     if File.size(file) < 100 * 1024 * MORE_LOGGING
       File.read(file)
     else
       contents = File.read(file, 100 * MORE_LOGGING)
       "#{file} is over #{100 * MORE_LOGGING} kbytes - too big to
        display in the dashboard, output is truncated\n\n\n#{contents}"
     end
   end

 end