Like I said, I’m not sure myself, just repeating what I read here http://www.altimas.net/faq
"Q) Is the Altima and the 240SX engines the same and if so what are the differences?
A) The motor are basically the same. The 240sx had a little higher compression ratio, and had some cams before they died that gave them a little more horsepower, something to the order of like 5 or so. Internals for both motors would be swappable. For example you could swap out the altima pistons for 240sx pistons and bump compression up a little…"