Before I start I searched up on this and got conflicting answers, I called mazdatrix as well to get a better understanding... here is my dilemma..

I accidentally picked up s5 UIM and LIM when I got confused by pictures, some sources say that works, others say it does not.. I just wanna verify before I sell them and get the S4 ones.

So do s5 TII UIM and LIM work on a s4 TII block when emission controls are not a factor and has a large streetport? It seems to physically fit.. let me know please.

 

Try it. It should bolt right up and if you don't care about emissions then you should be fine

 

you will need the appropriate fuel rails and the top mount intercooler if you want it, other than that, its the same bolt pattern.

 

The S5 T2 intake port runners on the irons are bigger. S5 LIM to s4 irons is not an ideal match really. If you compare the LIM gaskets between the S5 and S4 you would see what I mean. There will be a step for the air to climb over.

When I built my engine I ended up switching from s4 irons & s4 manifolds to s5 irons and s5 manifolds.

 

ive got s5 manifolds on my s4 block and they work fine. the only issue is you need a few washers as spacers to mount the secondary fuel rail.

 

Step? like it just will be a bit turbulent or saying that the manifold just wont seal well?