A 25 head has hydraulic lifters...26 solid... fair enough the ports may be the same size and if ur revving to 7,000rpm they may be comparable....
what if ur revving to 8500rpm...the rb25 head i dont think will be as efficient as a 26....
cost benefit analysis.....if ur motor is apart, ur a bit lost if u bought a greddy manifold for $1000 and put it on ur rb25 then some decent cams for $1000 when a 26 head is $1500....its got the manifold, bigger cams, solid valve train (which u can pay tomei $1500 for to do the conversion to a rb25)
i would personally put the 26 head on if uve got the opportunity...... in regards to combustion chambers being different i not sure about that... maybe some1 can fill us in with some more information to whether it is possible and what to do....unfortunatly we do not all live in perth and have ur workshop at our disposable...so instead of bagging out the potential modification maybe input into it....
i believe the exhuast valves on a rb26 is larger warpspeed and i do agree with ur vvt theory....how many ppl really care how much power they have before the vvt switches off?? lets say approx 4,500pm....a 10-20 rwkw difference at this rev does nothing for me? then again its an adrenalin rush for others :headspin: :headspin: :headspin: