Maxt

It does make difference, with the same amount of timing, the flame starts earlier on the recess of the rotor with an s5 housing, there is a power difference between the 2 sets of housings and spark plug location. It also changes how fuel efficient the motor is. With the s5 and FD the flame front can be started at the front of the recess with a lesser amount of ignition advance, to get an s4 to start the burn at the same point of the recess, it needs more advance, which increases the chance of knock, its part of the reason the compression could be bumped from s4 to s5 na and turbo. The s4 location is said to be better for super high rpms, when early advance is needed. But with the slightly earlier burn start of the s4, the pressure wave would push the charge below the flame front and compress it, causing it to knock at a given e-shaft angle, lower compression was apparently the first step around it, but by starting the flame front earlier and the same e shaft angle, it reduced the amount of unburnt charge below flame front to knock.. And compression could be raised once more, since the motor was less detonation prone.

It doesnt matter that they dont fire at the same time, 2 differnt power levels will accelarate the e-shaft at 2 differnt rates, doesnt make for a smooth running motor, god know what it would do to the harmonics in the motor, if power leves didnt matter between the rotors, Mazda would not have bothered with a compression variance number..

iceblue

20psi variance thats allot for the tolerance. The power difference found from that and the change of timing locations is far greater. But the harmonics are more forgiving hence why they can get away with 18gram rotor weight differences on balance when a piston is at 3-4grams allot of times :-/. Being NA on a stock ECU the motor should not exhibit any viewable changes.



However that housing was pulled from an S4 block I suspect reman on measuring of the hole locations I saw no variances I actually been puzzled on that for a few weeks but decided I really didn't care that much. I used a straight edge and a lazer level to measure them.

Maxt

And your proof of that is what?... The bottom line, is dont mix housings.. the spark plug difference was enough of a difference to not only raise boost, but also bump compression .5 on the s5 and FD engines, but also allow a .7 change on the n/a engines.. Thats significant.. And people wonder why engines blow, and dont last..

iceblue

There is allot more to thous numbers then just a trailing plug hole alignment in fact its virtually irrelivant. Hell you could even take the trailing plugs off and virtually see no loss in HP. We all know they are there to control the flame front from the elongated chambers. But fact is if they are actually different in thous housings and my lazer lied it wont matter a damn with this setup.

Maxt

Its not even the trailing plug we are talking about here, its the leading plugs that have the different location between the different series of housings..

You really think that mazda would go through the process of changing housing tooling for no significant purpose? lol.. Thats right up there with, that big gouge doesnt matter, and 3mm seals are tougher..

Trailing plug doesnt matter? Put some dyno time in a an engine past 6000 rpm and ask yourself why the newest MFR housings have not only 1, but 2 trailing plugs..

iceblue

Well from the data I have collected and I said it does make a difference bu the amount is very minute of a motor similar to this one. Almost guaranteed under 3hp. I don't even want to start on the 3mm joke. The MFR housing could have many reasons we do not know. Perhaps fuel type? The significance in fuel in incredible hell why do I pay $17 a gallon for 101oc fuel for my race bikes?



I can guarantee you on my life the spark plug holes were in identical position on this motor and housings. So that still leaves the puzzel when and why and how much did Mazda change. they have done this before changed castings and not all the parts and people go off claiming there series changes and there not officially. The motor the "s5" housing came out of was a late model 88FC with S4 plug timing and S5 outer casting.

j9fd3s

good stuff!