Aaron Cake

iTrader: (1)

Not sure as I've never seen it done. I could ask my machinest if you want, but you probably have a local shop you can send your stuff to instead of shipping it all the way over here...

Amur_

From the way some people talk, you'd think it was worth a few inches elsewhere.



As for machining:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/testimonial-ra-3mm-seals-412218/

PM RotaryResurrection and ask him who machined those rotors, what was paid and how difficult he thinks the work is...


If you don't get a reply within a week (hey, he's a busy guy!) let me know.

coldfire

iTrader: (1)

i didn't see this thread the first time around.
anyways, i would like to try to address the issue of increased wear and forces that a 3mm seal would cause over a 2mm.
the first issue to consider is that the motion of the rotor follows that of an epitrochoid curve, a type of cycloidal curve. i have not studied, and i do not think that i will ever, the specific nature of forces on this type of curve. HOWEVER, due to the fact that we are basically dealing with a smaller circle rotating about a larger circle, we can just assume uniform circular motion on the edge of the outer circle.
so, continuing with this assumption:

- i'm not quite sure of how much heavier a 3mm is over a 2mm, but i heard 3 grams?
as for the mass of a 2mm seal, i have no clue. but we just want the difference here.
so
m1=m
m2=m + 0.003
radius (distance from seal to center of rotor) ~= 0.11m
velocity at 2400rpm = (2400 rev/min)(2pi*0.11 m/rev)/(60 s/min) ~= 27.6 m/s

...doing the calculations, we can see that adding 3 grams adds about 2.29 N of force at each corner, or about 0.233515 kilogram-force. not quite sure what to make of this conclusion though, lol...

edit: btw, 2400 rpm on the rotor will be about redline for most of you, considering the apex seal will see 1/3 rpm of what your tach reads...

smnc

For the record, GSL-SE motors use 3mm seals stock, and are generally regarded as the most durable RX-7 engine...

Maxthe7man

Any data to prove that outside of anecdotal?..It was also not a turbo engine either so the thermal loading and ouput was significantly less.. The last incarnation of the turbo 13b was rated about double that of the gsl-se motor.
I recently picked up a book that is printed only in Japanese that covers every aspect of the rotary from the earliest days to the renesis, written in collaboration with some of the engineers from mazda. This is the rotary bible if there ever was one. It takes me 2 hours to read each page so dont expect to regurgitate the entire book.
There were a couple of aspects from this book that are relevant to this debate, since it covers the 2mm vs 3mm debate in regards to performance , and durability.
First Jreynishs post is largely correct about the weight and the extra loading, although not truly circular or there are points of rotor dwell where there is no outward force on the seal, none the less it result in more loading. Another aspect is the enlarged cavity underneath the 3mm seal, mazda cites this as a major area of compression loss, and also the reasonig that 3mm motors compression spec is 5 psi less than the 2mm motor, they found that the more gas pressure underneath the seal had a detrimental effect on performance and durability, although is helped the seal of the larger seal, it also loads the chrome surface more heavily resulting in greater housig wear and friction, from a two fold effect, first the contact area of the 3mm seal is greater on the housing, but also on the gas side, so more seal is getting pushed into the housing harder. It states that this change alone made 35% difference in the amount of housing wear over a fixed period of time, but internal friction was reduced overall by 15% which is significant. Overall the change allowed the motor to rev higher and seal better, and changing to 3mms aint gonna make the motor detonation proof.. In fact when I had injecotors get jammed shut I pinged heavy enough to dent rotors on each face, and the 2mm mazda seals did not break on those faces...
Something else I knew before but is also on this book, is the change in the shape of the rotor and housing from the 2mm to 3 motors, I have been told by alot by more than one top Japanese engine builder never to mix parts from differet series and production times, yeah we have all done it and gotten away with it, but I believe there is more ouput to be had by following that rule. There is alot of power hidden in a build of a motor outside of porting.
Hugh have you dynod your car with your mods on a 2mm motor?
Max

smnc

Hey, I'm not looking to open up a big debate.
I don't have any stats, just a general base of annecdotes.
And even if it is a fact, I can't say it's directly related to apex seal width. I was just mentioning it as a point of general interest.
And of course you really can't compare them to tubo cars for durability. The best comparison would be to a 6 port NA fc.