but onto the subject at hand, the RB23/4, bang for buck, just isnt going to cut it.
if i was in your position, id definitely be going for the RB25/30 combination with a DE head (id imagine the non turbo nomenclature would make them cheaper as a bonus compared to DET heads).
get a '30 block, non turbo should be right, but if you can find a turbo block for the right price, snap it up, bolt the 25DE head on top, strap a turbo and fmic on it, and enjoy life.
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the turbo block is identical pretty much to the non turbo block apart from the pistons, you do not want to use these pistons as you will end up with way too lower compression.
Brenton: Go with the 25/30 combo, do as cubes said and grab a running rb30e, check compression etc to make sure its top notch. then find an r32 rb25de head, whack some GTR valve springs in and you'll be laughing!
Trust me, you won't regret it as the feeling this motor gives you when driving is awesome and definitely worth it in my opinion!