i took a look at my completed short block and discovered i made a dumb mistake and mixed the front rotor housing for the rear and rear for the front. I am building a S4 NA with T2 S5 housing. I already blocked off the water passage, will this mismatch matter on a S4 NA build? air passages? They both look identical to me.

 

did you put both turbo or both n/a exhaust sleeves in? and you have 1 S4 and 1 S5 housing?

mixing the positions only blocks airflow to the manifold ports from the ACV, which only affects emissions and idle quality marginally.

i'd be more concerned about the difference in spark plug timing of the series housings, you really shouldn't mix housings like that.

 

If i understood right, he's using S5 t2 housing on an S4 N/A build, Not two different series housings.

 

Justin is correct, I am using two S5 T2housings. I mixed the position for F and R, I misread the stamps on the housing. Will this be a problem?

 

even though they were marked, they are interchangeable

 

only if you need to smog it. actually, you should check, since every engine except the S4 NA has the air injection going thru the center iron and into the rotor housings from the side facing the middle, and the S4 has the air injection coming from each end iron, you might have gotten lucky.

 

what would the air injection hole look like? I am not quite sure what I am looking for on the center iron. the housing look completely identical to me on the outside.

 

I hope you put na exhaust sleeves in it! its unreal how much louder a na is with out that exhaust port diffuser thing!

 

no sleeves and street ported.

 

That's why you buy a full exhaust system as opposed to a straight pipe with a 3 or 4 inch can on the end of it

 

even if you do have to smog it the port air isn't critical to passing.

i wouldn't lose any sleep over it.

physically interchangeable, yes. technically, no. the housings have holes drilled into the exhaust passages to assist in cleaning up emissions. look at a pair again and you will see a port leading to the exhaust that is specific to F and R.