94touring

Well if your going to over rev an engine, a rotary would be the engine of choice...theres only 3 moving parts. I've missed shifts or got lazy and revved to 9k before with no ill effects, but its not something i really want to make a habit of since I didn't set the engine up that way when I rebuilt it with my old used housings and rotors.

94touring

Also to the guys who have a lot of engine experience. Is there any truth to stock apex seal springs allowing the seals to flutter at really high rpms? Would a heavy duty spring be a good idea for a high rev application?

little rotor

The whole rotating assembly is dynamically balanced from factory. Therefore a pair of rotors (keeping the rear to the rear and front to the front) and both counterweights form a balanced set. Changing any one of these componets will upset the balance. That includes replacing a rotor if you damage one. For this reason Mazda stamps a letter A-E (I think) on each rotor. In theory if you damage a rotor your should replace it with one of the same letter (and therefore weight).



Alternatively, you can send the assembly out and and get it rebalanced. This is a must if you have the rotors lightened. However this is a bit of a black art because unlike a piston engine a rotor has a mass of oil sloshing around inside it. How much? Who knows. I'm sure there are people out there that know how to get it right, but as a general rule Mazda does a good job, so if it ain't broke don't fix it.



However even if you take no notice of all of this the outcome isn't the end of the world. At worst the engine won't like to rev quite as high and may wear the bearings a little faster.

WickedFD

"Current versions have "Three-window" main bearings (and a special groove inside the stationary gear) for improved lubrication. Tooth load on the stationary gear is one of the limiting factors in allowable maximum RPM of a rotary engine. Stock gears begin to deform over 8,000 RPM, but hardened gears are available for higher RPM applications." -rotory engine illustrated.



what do you guys think about this? Did you guys change your st. gears?

j9fd3s

my 1st gen with an s4 na block sees 8500+ regularly, 140k on the motor



mike

IGY

Actually FD's stock stationary gears are hardened. That statement would be correct for FC and older rotaries. Cosmo stationary gears are the same as FD.

IGY

They are not balanced as a set. You can use any two same weight same compression rotors together as long as the letters on the rotors are only one off ie; A and B, or C and D. This means you can run FC kouki rotors with FD rotors or Cosmo rotors. If you want to rev higher, yes it is safer to use same lettered rotors. My bridge ported motor actually had one FD and one Cosmo rotor, 10.5 all day long.

vosko

They are not balanced as a set. You can use any two same weight same compression rotors together as long as the letters on the rotors are only one off ie; A and B, or C and D. This means you can run FC kouki rotors with FD rotors or Cosmo rotors. If you want to rev higher, yes it is safer to use same lettered rotors. My bridge ported motor actually had one FD and one Cosmo rotor, 10.5 all day long. [/quote]

that is good to know!

little rotor

I agree that when Mazda builds an engine the rotors will be either the same weight or one letter away (from what I've seen of engines I've pulled apart). However I disgree if you are saying that a set of counterweights and rotors (in their original position) do not form a balanced set.

It's not just to say that that if you have matching weight rotor than it will be balanced. Lets say Mazda used a C for the front and a D for the rear. Then the front and rear counterweights have material removed to balance the rotating assembly. Now you pop the rear rotor. You shouldn't just throw in a B or a C (although the C would be better) weight to replace it. It should be replaced with a D.

Now thats all the theory off it. In practise you use what you've got. But if you have the choice (i.e a shelf full of spare rotors like me ) then use what came out of it.



IGY, by FC kouki you mean 89-91 right? Does kouki mean 5 in Japanese?



I also agree that 89-91 FC, Cosmo, and FD all ok to mix and match. Although I have noticed different shapes of the dish carved in the rotor between some of the models. If you really wanted to be fussy than ideally you would run two of the same shape. Earlier FC obviously can't be interchanged due to the different compression ratio.

rx7tt95

We did check the rotor letters and they were within "spec" and we used the front on the front, rear on the rear. Worked out well. My FD's were identical to the Cosmo rotors appearance wise. The Cosmo stationary gears are not hardened like the FD's either. They use the older FC-style three window bearings whereas the FD's have nine (or was it seven?).



My only concern at the momen then is oil pressure....anyone remember what they're getting pressure wise under full boost? Vosko? If I remeber correctly, I was seening 100psi (according to the gauge) which I initially had with the new engine. It's now down and I see about 60psi under boost which really isn't enough. It "may" be the sender as it's the original, 71K miles.