yep. the na's have a different exhaust sleeve though

I don't know the turbo engines too well, other than that they had knock sensors.



A friend of mine does have some S4 Turbo bits lying around and there are drilled/tapped bosses above the trailing plugs, I would assume those are for knock sensors.

Like I said before, this train of thought goes against what Ive always thought about S4 turbos, but anyways... Why would mazda cast bungs and tap them for the knock sensor on rotor housings when S4 knock sensors are on the center iron by the oil filler tube? I could see in S5 and S6 where the knock sensor is actually in the housing, but I dont believe its the case with s4.

Parts commonality? It costs less to make all of the parts with a drilled/tapped boss than it does to figure out how many drilled/tapped and plain housings, then do production runs of each, twice as many part numbers to inventory, and so on.



How many rear side housings have the machined, drilled, and tapped flange for the old top mount starter, complete with casting depression in the cooling passage? If I'm remembering right, they kept that feature right up until the 13B-REW.

as far as i know, you can tell an s5+ housing form the knock sensor hole, the s4's had the knock sensor in the center iron.

ok,so how bout this.



i get 2 n/a 13b housings,put my s4 turbo sleeves in them and i have 2 turbo housings at fraction of the cost.do-able? yes or no?

yep. over here that doesnt work, cause new na and turbo housings are the same price, and used are all bad

i know where you have been mislaying the facts

housings firstly-



turbo and non turbo housings of the same year are the same, except for the exhaust port insert

( NA have the baffle )



s4 housings ( which do not have the threaded knock sensor hole )

have different leading spark plug locations to s5/s6 ones



as for the chrome-----

the s4 ONWARDS housings have a revised trochoid calculation and surface

- this is because when the 2 mm apex seals are in the "lay down" position ( trailing edge not perpendicular to surface )

they do not express the same dimensions as a 3mm seal , and the housing has been resurfaced bigger to suit

( compared to the GSL-SE and before housings )



rotors -

the TURBO s4 and s5 ROTORS have chrome plating to the apex seal SLOT, when NA ones do not

as a result the typical apex seal when installed is fractionally tighter fit

TURBO side seals are also moly disulphide coated, NA ones not





PS

i have used earlier 3mm rotors quite successfully in late housings, despite very small trochoid differences

i have used NA housings sans the insert AOK on turbo motors

i have successfully used 9.4 2mm ( s4 NA ) and 9.4 3mm ( GSL-SE ) rotors no problem in s4/ s5 turbo hybrids

i have not payed much attention to finding moly side seals either, both perform fine

I have laid Series 4 rotor housings dowel to dowel on early housings and I couldn't detect any place where the dimensions were different. A straightedge laid across the surface laid flat against both housings at all points.

while i have seen it myself, and also read it across many sources

- i suggest you read page 3, article B

even cerment agree

the housings change trochoid , especially when it went from 6 mm to 3mm and from 3mm to 2mm apex seals

http://jhbperformance.com/downloads/jhb-te...performance.pdf