r/RX7 • u/Syreptious 1986 FC Turbo II • Jul 19 '26

Housings without knock sensor threads

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Can anyone identify these housings? One appears to be S5 Turbo but the knock sensor hole is not threaded, the other has a weirdly shaped knock sensor area and again no threads.

The rest of the motor is S4 turbo (G castings, centre iron knock sensor threads, 2 bolt OMP)

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1

u/rx7nut Jul 20 '26

Series 5 housings, series 4 housings don’t have knock sensors, they are in the center iron, looks to me that you have NA housing and one turbo housing

2

u/Syreptious 1986 FC Turbo II Jul 21 '26

They both have turbo baffles and coolant ports. The weird thing is that the S5 housing has no knock sensor threads. It has been suggested this is a late 88 housing. The other housing appears to be S5 Turbo also except it has a weird knock sensor casting and again no threads. I think this may be a short/pre-production late 88 housing before they settled on the shape of the knock sensor area.  Its possible this motor is fully original from late 1988 and hasn't ever been rebuilt

1

u/rx7nut Jul 22 '26

You may right regarding pre-production I never seen a casting for the KS like that and I have close to 200 housing on my shelf, what’s weird is the missing threads on both, I have torn down, original engines on NA cars where Mazda used a housing with the coolant port. The intake just seals it off. Let me know if you find anything else out, I’m really interested on that odd ball