s4 s5
 

what is exactly the difference because im going to order a jdm engine off the net and i dont want to have the wrong one so i appreciate the info

????? theres a huge list of differences, the question is what type of car do you have? also you know the chances of a jdm motor being good are like 1:4.

Copied and pasted directly from the FAQ:

How do I tell the difference between an S4 and S5 engine?
See the following topics:
https://www.rx7club.com/forum/showthread.php?t=530583
https://www.rx7club.com/forum/showthread.php?t=263870
Lots of Info: https://www.rx7club.com/forum/showthread.php?t=373451
Pictures: https://www.rx7club.com/forum/showthread.php?t=341891
https://www.rx7club.com/forum/showthread.php?t=330057
Good thread: https://www.rx7club.com/forum/showthread.php?t=594874

The FAQ should be the first place you check before posting a question.

The long and short of it is that the S4 and S5 are two totally different cars and have very different engines. There are ways to make it work, but you should stick to your series.