although the question of how much is needed to swap a sr20 into my 240 is asked a lot we dont have a sticky for it, so ill try my best to lay out all that is needed and how much it'll cost you. my experience is from putting a redtop into a s13. if u have a 89-90 240sx: besides the motor, you'll need the power steering lines from a 91-94 ka24de 240sx, and the ac compressor. if u dont want either of these to function, then obviously u wont need them.THE SWAP. prolly the best way to go would be to get a complete front clip from a reputable distributer,
http://www.srswap.com http://www.venus-auto.com phase 2 mtortrend and a few others. but ebay can be a problem, and its usually more expensive for the clip. a clip will come with the motor, ecu, wiring harness, everything under the hood, and the transmission. the transmission bolts up to the stock driveshaft of the 240 and the motor drops into the 240 engine bay with no mods. if u just get the motorser, engine and transmission, sometimes ecu and harness if ur lucky, u will need many other parts to finish the swap, ie: ignitor chip, maf, coilpacks sometimes, etc, it can end up costing more and u will have to find these parts costing time, so just get the clip. on my clip, i had no downpipe, but many places stock these for around $130. heavy throttle also sells ez install kits with new hoses, and tune up kits, with new plugs, oil and fuel filters, and belts. some people argue that gasget kits should be ordered and installed to replace all of the gaskets on the motor while its out and easily accesible, these run around $250. i also got a walbro 255 lph fuel pump as the stock 240 one will only work under stock boost, if its in good shape, i got mine for $100 shipped, off ebay, brand new. so lets recap:sr20det redtop front clip......$2000-$2500install.........$1000-$2000 depending on ur year and what the shop charges.fuel pump....$100gasket kit ......$250downpipe.....$130if u want u can buy the front clip and have a shop do a harness service for about $100, they take the ka and sr harness, let them mate and u have a plug and play harness. otherwise u have to modify some plugs, this can be found also on
http://www.srswap.com under faq-wiring. so ur looking about $2500-$3000 to do it all ur self, but its always a good idea to have some extra cash just in case, and for any unforseen problems.
http://www.sportcompactcarweb.com did a write up of their sr swap, its not too extravagent but its a good basis for you to start. srswap.com also has a lot of info for the swap. most of all your other questions have prolly been answered, use the search button, it is your friend. if i have forgotten something, go ahead and add it on.