I measured the distance from the apex seal to the start of the dish. It seems that they are ~43 mm one way and ~46mm on the other side. I thought they were supposed to be the same IE the dish is centerd on the rotor????



Thanks



Gregory

i measured a couple s4's and they were not very consistant at all. they were to about .100"

http://www.mazdausa.com/MusaWeb/displayPag...ineRotaryPiston





If you now turn the engine to 20 degrees BTC, the way is open to burn into the mixture in the rotor depression. This is an important part of the reason why nearly all 1974 and later engines can run no more than 20 to 25 degrees ignition advance at high power (earlier USA model engines had a very long, shallow depression that allowed more advance). As I explained earlier, there are some parallels between rotaries and recips here - combustion chamber and piston top design are major concerns in recips - but there are some distinctive items to consider when working with rotaries.



The truth is, there isn't a lot that you can do to change the shape of the combustion depression, especially in 1989 and later engines with thin casting walls, but you can do some useful things. For one thing, you can ensure that the distance from the apex seal groove to the leading edge of the combustion depression is the same distance on all flanks of all rotors so that all will tolerate the same ignition timing (grind the leading edge of the depression as necessary).



Next, you can try to reduce heat transfer into the rotor by polishing the combustion depression and/or coating it with a "heat barrier" coating (Note: Do not add any measurable thickness to the curved flank of the rotor, otherwise the rotor may hit the rotor housing). Many recip racers do the same sort of things to pistons and combustion chambers, for the same reasons.

Wow, cool article. I wish he would have gone more into the coatings. I'd also like to know how much grinding the leading edge of the S5 NA rotors can take, so that more advance can be dialed in.

Zenki FC rotors had a production tolerance of 0.2 deviation on the CR due to casting methods.



Later rotors that were machined dropped the tolerance down to 0.04 CR, which is pretty much negliable.



I wouldn't worry about it.

It's not like you can do anything about it. :(





-Ted

I am in the process of making the start and end of the dish exactly the same. I am not going to worry about cr at this point just the timing. I could always cc the dishes but thats more work than I am willing to do at this point.



Gregory

you can change the s4 dishes a bit, but that also will change the volume, which is bad. i just measured a few rotors and set em up so that the closest tolerances are for the leading side....