Besides the obvious what are the internal differances between the 25 and the 26? Are the cranks, rods, ect.. the same and what are the flow differances between the two heads or are they the same? I am seriously considering an inline six swap, and wish to acheive somewhere in the mid 500hp range, and was concerned about the rb25 internals at this power level.

Thanks

 

The 26 can hold that power range + on its internals. However the 25 can to but I would recommend not doing it daily anf it may not last long. For the 25 you can use the 26 bottom end and have no prob with the 500 range. I dont know the head flow numbers so cant go there.
The 25 is allot cheaper to start with than the 26 thats why I went with it. The final stage in my project will going to the 26 N1 bottom end which is stronger than regular 26. But if you want to achieve a reliable 500 with out going internal pay the extra money in the get go and go for the 26.