Just to clarify. The port opening timing is different between s4 and s5 tii irons correct? (by about 10 degrees.. i think s4 opens later?)

Anyways since this is the case.. that means i cannot build a turbo motor with a s5 turbo rear iron, s4 turbo mid, and s4 turbo front?

And just to save another post. I can mix s4 and s5 turbo housings together though right?

Any help would be appreciated. thanks.

 

I believe the housings have the spark plug holes either farther or closer together between s4 and s5 so they cant be interchanged. So the plug timing would be different.

 

mate i only deal with jap or aussie engines and i know you get a different spec middle plate over there for your s4
( and also the turbo housings with odd spark locations )

but this is how i see them
( and take in mind i have disassembled many examples of both )

for jap and aussie, we get s4t engines that use G,G,G plate combinations
for s5t jap and aussie get D,G,D

the difference in the D and G secondary plates
is that on a D the runner track at the manifold join is port matched for a few mm deep
the front D plate also has the larger oil passage O ring land that requires the nylon outer ring
and the rear D plate soon into the production run ( but not initially ) gains the wedge under the oil filter dowel for extra dowel support

the porting between D and G secondary plates is identical, and i have often had them side by side to compare

since both s4 and s5 turbo engines from jap and aussie share the G centre plate, it can be argued that the porting is unchanged and the changes are only detail

the US N332 engine ( s4T ) is a different bird, it has the odd spark locations found elsewhere ( worldwide ) only in the s4 NA
it also uses the plate config ( AFAIK ) G,Z,G
and so it would be true to say that US s4 ,, and US s5 turbo porting is different ( primary only )
and that only detail differences lay between the US s4 and US s5 turbo secondary plates

US s5 turbo AFAIK is same as jap and aussie versions ( D, G , D )
and uses the G middle plate with port size intended to induce a little internal EGR effect with its slightly earlier port open timing
( and so you see why jap s4t engines had no external EGR, and curiously the aussie s4t cops external fittings and internal EGR port config )


what that means to the OP, is if he puts the D and G secondary plates side by side he should notice no change in port timing
- and a minor change in runner diameter for a few mm in from manifold edge

and as such i have used such plate combos and seen no ill effects at all
for the OP, his main changes will be in which middle plate he chooses to use,, the G being the larger choice
however for the OP, in the US turbo s4 housings dont interchange with s5 turbo housing ( due to sparkplug locations )
elsewhere in the world this is not entirely true, as most markets only have s4 NA housings that are out of pattern in the plug locations

 

yes you can mix and match S4 and S5 turbo irons, the S5 irons port runners are about 1-2mm larger than the S4 but it isn't enough of a difference to the engine. if running S4 irons on a S5 though you should port the runners to match the LIM ports as they are smaller.

S4 and S5 housings on the other hand cannot be mixed, they have to both be the same series.

 

awesome info learning a lot. usually people just say yes you can use this and end it at that. its nice to know the details why this is possible!.

 

no problem, i would explain the differences between the S4 and S5 rotor housings but i've done it so many times now that i'm burnt out on it. basically the spark plugs are timed differently between the 2 series of USDM engines. many people run S5 rear irons on S4 blocks because some runs of S5 rear irons had a thicker dowel pin land, giving the engine more rigidity for severe horsepower applications(400+ wheel horsepower) where the S4 rear iron tends to fail at varying levels much above around 350 wheel horsepower.

 

i wish i would have known this about 2 months ago. I was told s4 and s5 rear irons were not interchangeable. I was right around that power range when my s4 rear iron took a ****. It was put back together with a new, used s4 iron. If i would have known, i would have bought a s5 rear iron.