rb20det= 2 cly turbo inline 6
rb25det= 2.5 liter inline 6
rb26de= 2.6 twin turbo inline 6
ca18det-1.8 4 cly very old and not worth it in my opinion
If you want to stay nissan turbo inline 6 I can get any jdm motor for you. I just came back from TN and bought a 93 mint 240sx coupe for $1500, 100% rust free, perfect interior, and perfect outside. I can get you the whole half skyline for less then 2k to your front door. The trannys in rb's are beefy as crap and are good till around 800hp and the motor is good stock internal for 550-650 hp others have taken them above but I would not recomend doing so.
BIG TURBO and big fuel and its endless for power, they make ass loads of torque and power. unlike 302 blocks they will never split in half everything is forged from factory. If your just looking at 400whp you can do that with the stock twins on the car. There are guys in ohio that have gone 10's with the stock twins.