j9fd3s

yeah, exactly, it runs ok, but its not ideal

BDC

I think the question is: When does "not ideal" become "detrimental"? Based on what I can gather from what Luke's talked about, I think his point here is to potentially eliminate the idea of this rotor housing combination as being at the root or atleast in part of the cause of his motor cracking. While I feel it's not related per my own experience of having run certain things more aggressively over his setup, I think it's a reasonable thing to look at and question, at least at first blush.



On my car, I ran this same combination for about 2 years. It was the same period of time that I made 424rwhp. I hammered the hell out of the engine, frequently hanging off the 8200rpm rev limiter and running up to about 17psi of boost. I was using 17* leading advance with a 5* split at the time on the then-93 octane pump fuel (mostly in early year 2000).



I agree with you Mike; it might ultimately not be ideal (afterall, as Max mentioned, Mazda invested time and no doubt money to change something on the rotor housing design and assumedly for the better), but it seems to work alright. I've had no issue; not a single one using that combo.



B



Edit: Grammar fix

Comitatus

Here are pictures that I just snapped. I slid a dowel pin through the land to ensure that they were lined up evenly.



True S5 TII rotor housing from original motor on left (front), and S4 housing on right (rear)



Compare what you will.

Fishey

I honestly think that it will make a difference based on my experiance since it will throw of the timing between the two unless you account for it in programing. The difference might be slight but its going to work out to about .5degree. Since you take 360degree segmentation and I would guess the small amount they are off is about .5degree in actual timing.