supposedly one of the changes to the 05 is that they ground the combustion chamber smoother hence lowering the compression to 12.3-1 and getting better flow. also they say it runs better with the lowered compression. is it the same head as 04? and if it is would this be sumthin' to try if you could figure out where to grind, doesn't sound like a bad winter project the only thing that would worry me is grinding too much,i guess you could find out what cc's the 04 chamber is compared to the 05 and make a plate with a hole that bolts to the head turn it upside down and carefully measure how much water it takes to fill it(nascar trick!)then grind till your about the same.any input?