Halfway through my second build (S5 T2) and I noticed some scratches I wasn't thrilled about on the rear housing. The rest of the rear housing, and all of the front housing, looked really good, except for these two scratches. They are lined up with the top plug hole and are each deep enough to catch a nail on, but not too bad. This is also right in the area where they will affect compression the most. Here's a picture:




and another through a 10x loupe:





The engine is being assembled mostly with used seals, trying to get it running economically at a lesser power level than before. (400whp before, maybe 250-300whp now.) The used seals have about 2500 miles on them, first engine broke a side seal because I clearanced them wrong. I'm wondering if anyone can give me an idea of what the specific effects of using this housing would be, or if it's worth the $330 to have it resurfaced. ($150 per housing, it would probably be a good idea to have the other one done too, plus shipping)


Also, bonus round!

The first engine was assembled with housings of unknown vintage...I thought they might have been S5 T2 housings, but the rest of the engine was S4 T2. The new housings came off a series 5 T2 engine (with a series 3 front cover and oil pan!?)

The housings from the first engine are stamped "4" near the bottom, in between the two circles. The housings from the second engine are stamped "5" in the same spot. Coincidence? What do these numbers mean? Housings appear to have the same plug spacing.

 

Mazda doesn't use S4/S5, its an Australian thing. the Japanese say kouki/zenki, with the FC, and use a version number with the FD

the parts catalog just says FC3C-100001 or FC3C-200001 for S4 and S5.

i've never seen a number in the casting like that! they are S5 housings as they have the knock sensor holes. the little circles with the dots next to the 4 are a date stamp, if you were bored enough you could decode it, its simple, you just need to know which one is month and which one is year.

any housing made after 2004ish has one of those fancy bar code type things etched into it.

 

The number may simply be a cavity number. The housing is some sort of die-casting and they more than likely have several different molds. It's a way the molder can trace parts back if a defect or problem is found down the line with the parts.

 

I was almost certain those numbers didn't correspond to the generation. Mold/cavity number makes the most sense to me. The 4's are embossed (positive from surface) and the 5's are debossed (almost could be stamped in but too straight, probably from the mold as well)




Does anyone have an opinion on whether or not to use this housing, or what compression might look like if I do?

 

Well, after talking with BDC, I think I'm going to try and sand out some of this scratch and then run em. I'll try to remember to post back once I get compression numbers.

 

I'm no expert, but that looks perfectly useable.

PS
I have an S4 turbo housing for display, and it has a 2 on it, where yours has a 4. Whatever that means

 

That housing looks perfectly fine to me.

The external casting marks are meaningless for identification purposes. The above posted theory on that is likely to be the case...casting variances depending on the tooling used to produce the parts.

 

you could try lapping compound followed by polishing compound. I've managed to get a couple of timy scratches out doing that before.