i am looking to replace my 87 TIIs engine soon. it has 16k miles on it and it needs it. i was wondering waht the major differences were between an s4 and an s5 engine. would any of the parts from my s4 fit on the s5?

 

s4 has lower compression than s5.
but you can run more boost safely with a s4. basically bout the same out side from compression

 

You will need to pull the motor down to the bare short block. This includes removing the front cover to replace the electronic oil metering with your mechanical. You also will need to use your flywheel/front counter weight and Eshaft pully. You can possibly use the S5 intake/exhaust manifolds and turbos, but you will need to swap in your 87 tb, TPS ect ect ect, easiest to just use all the old sensors so you are sure they will all work. Since the car is MAS air it should correct for the slight bump in compression itself, but you will run out of fuel faster when you start modding because the motor will move more air than the S4 block. There might be more, we did this swap for a friend about 4 years ago if not more, so its been a while.

 

Educate Educate..

 

Sounds like "BlackFC" just about nailed it! I asked this question before to a Mazda service guy. He said that the motor mounts have to be changed also. How true that is I never investigated. What I would be asking myself is how much more money would I want to spend just to get an s5? Is it really worth it? IMHO, I don't think so. Good luck!