Rotor housing differences?
 

All right I've searched an been a bit enlightened. But can someone give a general rundown of the differences between S4, 5 & 6 turbo rotor housings? Thanks!

s4 has no knock sensor thread above T plug, s5/6 do. s5/6 have adjusted leading plug timing vs s4. s4 and s5 have coolant passage at the LIM, s6 does not. s6 has grooves on the "legs" that hold extra sealant, to further combat oil seepage from the oil in the oilpan area (this doesnt impact running of the engine at all), s4/5 do not. s5/6 seem to hold up better than s4 as far as wear, apparently a change in the coating process during manufacturing.

That's what I was looking for and pretty much sums up all the tidbits I've gathered. Thanks!!!

s4's do actually have the hole for the knock sensor. if you want to use the sensor in the s5 location, just grab a tap.

but the knock retard doesn't work anyway, so why bother?

No, no they don't. There is no "raised bump" to tap into. IF you tried to tap into a stock s4 housing, you'd hit the water jacket.

all the s4 motors i've had, or taken apart for other guys do have the bump with the hole...it's just not threaded.

i guess this could be like how they changed the front housing (s5 style) with the bigger land for the o-ring and nylon washer. i say s5 style, but i think they actually started using these front housings in late 87 or the 88's... not totally sure though.

Maybe so, or maybe your s4 engines were built once already. I have only seen s5 housings with the raised bump...and infact those had the holes tapped already, even on the NA versions.

I would say that I've taken apart a good 300 engines by now, and the number of s4's with threaded housings above the T plug can be counted on one hand, and explained as previous rebuilds with s5 rotorhousings.

they weren't threaded though.

you've doen a lot more engines than i have, so i trust what you have to say, although that's what i've encountered in my personal experiences.

but it's really 6 or half dozen one way or the other... who really cares?