Example...



I have an 89 S5 TII, when I had the motor rebuilt the first time, the rear rotor housing was shot.



It was replaced with a S4 NA Housing with the exhaust sleeves pulled.



My question is, after reading up on this subject, it is my understanding that the plug timing is different between my two housings as S4 NA is different than S5 TII housings.



Does this make a difference at all? Or do I have nothing to worry about. I'm running a Haltech E8, and makes me think that the plug timing will play a part somehow...due to the plug firing at a different point on the rotor face.



Any opinions or answers?

Notice the difference in these two rotor housings? Yep, that's my partially unshaven mug doin' some front cover stuff. That picture was taken in March 1999 and this motor was subsequently the same one I used to make 424hp in 2000 a year later.



Yes there's a difference in terms of physical plug location where the older housing has it skinner.. but, I never noticed a problem or any symptom with it at all and I ran a very skinny, very aggressive split back then.



B

Not doubting that it works...obviously it does work, because a housing, is a housing, is a housing.



Just wondering if it the ideal choice in housings. In my mind, when thinking that the timing is different because the gap between the 2 plugs is different, that would certainly have an impact on when the charge is ignited. This fact probably makes no difference in lower horsepower applications, but as the power comes up...it is my understanding that timing becomes EXTREMELY critical.



So, putting 2 and 2 together, I would think that it could affect things. Whether the effect is minor or major, I don't know, because I'm no expert. Just makes sense when I think about it.



As you know, with my recent engine failure...I'm trying to reduce ANY possibility of it happening again, so any factor that I'm doubtful on is being fixed/replaced.

Somewhere on here I regurgitated what I know about the spark plug differences from the Mazda motor book..

bottom of page 1 and page 2...



https://www.nopistons.com/forums/index.php?...c=68360&hl=

I have found some topics that touched, but none explaining in detail.



From what I have read...rotor housings should be kept to within a series because plug timing is the same within series.



I'll have to take a pic of my housings side by side. The trailing holes are fairly similar, but the leading hole on the NA housing is further up the side of the housing, toward the trailing hole, meaning more advanced. Since the 2 leadings fire together...can someone please explain to me how this doesn't make a difference?

Great! Thank you!



Reading that post and information makes perfect sense to me. The leading holes are in a specific location, and if different, of course it will make a difference as to when the charge will ignite.



Rotor housings should not be mixed in different series. Maxt is right, if it didn't make a difference, why would Mazda go about changing things up in the first place.

Any other thoughts, experiences from anyone?

ive never built an engine with mismatched plug holes.



i see how you can get something in the car running, but i dont see how it could be good

Max's post is sensible, but I've not seen any problem with it in experience. So, in my case, it's a conflict between logical principle and experience.



B