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The R34 RB25DETT or RB25 NEO engine is a or was a brillant step forward for Nissan. They managed to get it right this time around by getting a bit more aggressive with ignition timing. Hence the nice jump in power from the factory. At a rated 280ps or 275hp it is the same as the R32, and R33 GTRs. Rated that is.
In order to get more power however you have to increase cylinder pressures. This is done one of two ways or a combination of both. Either increase the forced induction, or advance the ingnition timing combined with more fuel. More fuel means it will have poor petrol milage. Nissan did it with ignition timing in this case.
Now your Cefiro will need some major upgrades to be able to drop the turbo motor in but less with the N/A motor. Your transmission will not handle the increased torque and power of either motor so you will have to change that. This also means your driveshaft must either be altered or changed. Since you have an open diff putting that much more through it will not get you anywhere since only one wheel is the main drive wheel. Putting in either will require a ecu change and if you want to go to the turbo RB engine a complete fuel system delivery change is needed, plus an intercooler and all the piping.
A few guys have swaped their RB20's with RB20DET's here in New Zealand and pick up second hand Skyline GTS-t ecu to sort that part out. This is a much cheaper option in the long term. Yes they still did the fuel pump, and intercooler but finding an evo intercooler here or other ones second hand is easy and not too expensive.