This is a very debated topic. I have the Tom Monroe book on rebuilding a Nissan motor, and it says both are siamesed...but later it says the F54 is siamesed with the water passages and all, and doesn't mention the N42 in the same little section. Even some Nissan techs say neither one is better for racing, and we all Nissan has done quite a lot of racing. However, be on the safe side and go with the block that Nissan turbocharged, the F54. 81-83 are the years they came turbo, and think of HOW many they produced in those years. Also, I'm not sure if the 81, but I know for a fact from personally owning one, and 82-83 NA has the F54 block also...so you have thousands and thousands of cars produced in that time frame, both turbo AND NA that are F54. Same block, crank, and rods.
So in summation, it will not be hard to find an F54 block. I bought a complete bottom end once for $50, and just recently bought the block, crank, rods, and pistons for $200. Both were within the area, so you shoudln't have to travel far. And in case you don't have a good selection of junkyards in your area, check out www.carparts.com...its a search feature for junkyards all across the nation. It won't be hard at all to ship a block.
yeh but you know what? ive e-mailed junkyards on that site and i never get feedback. there is a junkyard close by with about 4-5 z's. i dont know exactly which ones but they have them. so 81-83 N/A have the F54? i want to get one to build one up and learn about whats under the hood. also i dont have the time to pull my engine and rebuild that one since im in school and i dont want a shop to do it. i wont learn anything that way.
Well like I said, I'm not QUITE sure if the 81 NA had it, but I know for a fact the 82 and 83 did...so just get the NA block and get a P79 or P90 head from another place on that site. They do list phone #s also so you can call. If they're close, go check em out. Take a flash light so youll be able to get some light on the side of the block, then if you see the F54, KABAMM! Buy it. Motor complete, shouldn't be more than a few hundred bucks. Sell the parts you don't need and start your work.