I Recently bought a 10AE that has S5 rotor housings in the rebuild. for tuning purposes, how far retarded or advanced is the timing of the S5 compared to the S4? I have heard that there IS a difference, and just want to double check. thanks in advance!

Christian

 

there is a difference in how far apart the spark plug holes are. not a whole lot, but to me, any difference warrants matching parts. i couldnt tell you the exact measurement though, sorry.

 

It's about a 2-3mm location difference.

IMO, this does not really represent a timing difference. This is more like moving the location of a sparkplug in a cylinder head, than it is changing the timing event. Timing is controlled by the ecu in relation to the position of the rotor as determined by the crank angle sensor. Given the same ecu, the timing event still occurs with the rotor in the same position it would have been otherwise; the location of the plug when the timing event happens has changed slightly, perhaps for slightly more power or efficiency.

In either case it's pretty irrelevant..I've built s4 engines with s5/s6 housings, and s5/6 engines with s4 housings...it never makes any difference.

 

I'm sure in lower power applications, it probably doesn't have a detrimental effect..but the more power you make, common sense says that it could have a slight effect on timing. Probably 1 or 2 degrees.

I've done quite a bit of research regarding this topic, and there are MANY mixed opinions. So in retrospect, I would say it would better to err on the safe side, and keep things matched up.

 

is the trailing plug in the same position or are both plugs spaced outward from the S4 housings?

 

Thanks Kevin, the housings did after all come from you. this is swiftones old car.

 

I dont think I know who swiftone is.

I would not mix and match housings in the same engne, but I'd have no problems swapping housings as a set.

The trailing plugholes are identical, just the leadings moved down a little for s5+.

 

OK that clears up alot. thanks

 

slightly off topic, but is there a way to tell the difference between s4 and s5 housings just by looking at them? from the outside that is.

 

S5 has a spot for knock sensor

 

Here is a pic of the difference in plug timing between S4 and S5 rotor housings. These are both TII housings. S5 on left, S4 on right.

 

Common sense doesn't say that at all. Ignition timing is all about rotor position, as Kevin alluded to. Where the plug is has no effect on when the plug fires in relation to where the rotor is. The amount of power you make doesn't change that.

I wouldn't be surprised if the S5's revised leading spark position improved combustion efficiency, more specifically how the force of the mixture igniting is applied to the rotor. It's obviously nothing major, but manufacturers don't make changes like that for no reason.