difference between s4 and s5?
 

Can anyone tell me if there are any major differences in the s4 and s5 turbo engines? Are there any real advantages to using one or the other in my '87 turbo 2?

There are some minor changes. Intake runners are larger on the S5 engine, spark plug locations changed slightly, the turbo is more efficient and eliminates the mechanical twin scroll system on the S4. There are a few other minor changes...

Now, whether to use one or the other isn't a straightforward answer. If you have an S4 car and intend to run it with S4 electronics, stick with an S4 engine. Likewise for S5. If you plan to make 400+ HP, then go with the S5 engine as it has a thicker casting on the rear iron near the dowl. If you are running a standalone, you can use either engine.

Thank you Aaron. I have an 87 tII but it came without engine and tranny, and the previous owner had cut the wiring harness because he planned on putting a small block chevy in it. The new engine is supposed to come with a wiring harness and ecu. I think that i will be going with the s5 unless there is any major difficulties i will encounter.

if you use the s5 ecu, get the n370. the jdm n374 are junk and will not fire the rear rotor injectors but if you use s4 ecu i havent herd any complaints about them

I heard if the JDM N374 is chipped then you wont have the injector problem.

To the OP if you have a S4 T2 chassis its much easier to put a S4 T2 engine in than a S5 T2.

and what felix said it is a pain in the ass to put an s5 engine in an s4, i tried tha on my 88 gxl and ended up just parting it out. im not saying it cant be done but there is alot of unessery work