RX8 E-shaft vs 13B-RE/REW shaft
 

I'm left with wondering if anyone has had direct experience with the RX8 E-shaft in the same, or similar engine as regards to acceleration & ultimate torque. There is less mass with the renni e-shaft, but is it a noticable difference? I would imagine a dyno would see the difference, but how much?

I ask becuase I need to place an order with Mazdacomp on Monday for a new rear bearing/stat gear and thanks to Dans interchangeabilty thread, I'm going with the Renni piece. I'm wondering if I should just go ahead and get the e-shaft as well. Thoughts?

All I know is what I have read about in here:

http://rotarycarclub.com/rotary_foru...read.php?t=847

Yup, I read that thread.

Turns out there is SLIGHT scoring on the e-shaft. Enough to warrant replacement for $156. So now the question is, how much of a difference is it really going to make if any?

I have no evidence, or real reason for this, but this is what my guess is. I don't think it would make a huge difference in the car unless you are pushing big power out. It might be an interesting experiment to see how it would be different, but ultimately I think the gains would be marginal.

do it! .6lbs less mass to move is a benefit, do you already have a lightweight flywheel?

The ideal thing todo would be to use the same housings/seals and get before and after dynos. That will give you a better indication. I'm using all new seals and better housings.

Yes it is a benefit. It increases torque and ultimately acceleration. I'm running an exedy twin disc

thread jack!

What are you Air Intake Temps with that V-Mount?

It seems like it wouldn't be getting enough airflow unless you were using a vented hood.

its super nice, infact I'll be getting a V-mount of similar design here in the future.

Close to ambient ;)

The only time they get hot is when sitting still. I waited in line for an auto-x run right after a run, ~7 minutes waiting, and they got to ~110-115. The vented hood will help while stationary more than while moving. In my setup anyway.

do not use an 8 shaft for high power turbo engines.....You will be rebuilding it quickly....I am in a rush and have like 50 pms to return so after that I will post my experience

Define high hp please. And what experience do you have. I already ordered the thing, but I'm only shooting for ~375 out of this setup.

Well first I have been building rotary engines for a long time....

I built a 13b rew for a customer of ours at AZRR, his original had spun a bearing and the shaft was toast. So after some long nights talking to Maada Na engineers it looks like the 8 shaft was built in the same way as the third gen shaft. I had finite element data, mazda engineering data basically telling me that the shaft was built just as strong as the third gen..........

Dyno day come and we are hitting some pretty bad ass numbers right off the bat about 420 with 300+ foot pound with low boost about 13psi, out of the blue we loose 20% across the board. So I go to work checking spark and just about every thing, things get worse as we drive it then I start feeling it in the clutch bam it stops running. Take it apart and we have a bent shaft about .006 of an inch out at the front. This caused the engine to eat it self alive.


So, I went to the long task of figuring out why...so far what I can come up with, is there is an important tempering process that was not performed on these shafts for what I think is cost. the tempering alows the metal to deform and spring back this did not, it deformed and stayed there.

What is its limits, I am not sure but putting any kinda stress on these would scare me. So I will never build a turbo engine with this shaft again.:leaving:

That's very peculiar--assuming your correct one should be technically able to ship out the eccentric shaft and have it tempered. However, bending an E-shaft would seem counter intuitive if I'm imagining it right. Where exactly was the bend and how did you measure it, was the bend .006" from the front or was the measurement dictating that the shaft was out of spec by .006" in the front?

I ask because I would be very surprised that the stresses seen are orders of magnitude higher in a turbo built engine compared to the redline of the eight. Do we have the material mazda uses for the E-Shaft (what specific steel they use, etc)? I'll be happy to look up the stats on the material and see what forces would need to be present in order to deform it. I would also think that the REW's shaft would endure more stresses since it's rotational impulse is higher than the 8's (the .6lbs being more weight that needs to be spun up and down depending on the throttle puts more axial stress on the bearings--though the .6lbs may be of no effect or worry).

While doing google searches I came across this:
This is for 20B engines, but I believe the principle is still applicable. Was the original engine Pinned or Doweled?

crap, now I'm a little nervous. I do know that there are a few people running around with half-bridge + meth putting down 500 with this shaft.

Glenn, what sort of RPM's were you seeing?

I'm going to try it. I found some data on tests of the 8 vs the 7 shaft where the 8 was significantly harder than the 7. I'm not going for those kinds of numbers, hopefully it'll be ok.

My saving grace is Chadwicks been running his in basically the same motor that I have for some time now. Time will tell.

Nothing over 8k, here is the deal my man. It being harder is the issue. If you have a hardened piece of metal you need to temper it in order for it to be able to have "memory" with out memory it will bend and stay that way. Tempering will soften it in comparison to a non tempered hardened shaft.

Shaft deformation is something that is natural and will happen.

Look, I dont want to brag or try and make my self look great or anything like that I try and stay humble, to help you out let me give you a little background info.

I was trained to build the top racing rotary engines by Paul Yaw of Yawpower. I built all the engines that came out of his shop for the last 6years or so. Paul moved on to motec and injectors so no more engines, He helped Tom and I start azrotaryrockets.

We are also "sponsored" if you will by Mazda, i act as tech support for there rotary team and motor sports team.....

After coming from Yaw Mazda came with us, they send us project and customers, so I would say we know a little about this subject.

So take my word or dont ...I was aiming to help thats all....Good luck.

Ok, well some of your logic is flawed. The rx8 is an na engine with a low combustion pressure putting less stress on the shaft. You increase combustion pressure and you increase forces on the shaft. So for the sake of argument lets jump into black and white for a second. Combustion pressure basically aquates to torque, if you increase it the tourque will increase increasing the force aplied to the rotor, bearing and shaft. So with boost you increase combustion pressure. So with out the turbo you have less force on the shaft even at 9k.......Not to mention the torque on a renisis is well we all know that ./


Now if the shaft is bent .006 it is out of :mazdaspec" by .0045.


The shaft being bent .006 at one point of the shaft would give you a diameter of .012 meaning the shaft is digging .006 all the way around pushing the rotor out of place destroying the bearing etc.

Let me also say that i am not sure what torque rate you would have to exceed to bend this shaft but I know 300+ and you are going to be in trouble I doubt chadwick is anywhere near that..


I hope this all does not sound defensive I am about as articulate as a 3 year old on acid that lots there mommy....That s why I do not teach.

Shaft deformation is something that is natural and will happen.[/quote]

I wonder if the tempering is the reason why the 8 shaft is so much cheaper than the 7 shaft.

Do you remember what the clearances were on the main bearings? Could it be possible that some slop in the mains allowed the shaft to flex?

I appreciate the help. It's rare to get someone on the internet with actual knowledge and experience as opposed to spreading lore and rumors. Honestly, thanks for the advice.:icon_tup:

Yeah, pretty much my thoughts exactely. The combustion pressures and the torque produced by a turbo-charged rotary are going to be far greater than the torque and chamber pressures places on an N/A engine regardless of how high it spins

I didn't take it as defensive at all, so no worries.

I would suspect Chadwick is right around there. I should be abour 300 RWT and keeping it under 8k for sure. We'll see what happens I guess. I have a friend making ~450 RWT with that shaft and hasn't had any problems so :dunno:

Thanks for the input Glenn

Harder metals have a higher tensile resistance but a lower ductile fracture point: more likely to break than to bend--but this isn't always true depending on what metal is used, hence why I asked if you had the specific steel name on hand.

Spring back of a shaft would not stop damage to the bearings though--Will it reduce the problem; sure. Will it be the end all be all of failure. I don't see it. By bending the shaft in the first place that means in unequal force was applied to the two different combustion chambers at one ignition event (assuming balanced shaft). That would dictate to me that the flame front propagation produced more force directly perpendicular to the lobe than the other ignition events. Since the RX8 shaft has material removed from the lobe that would cause an "abnormal" ignition event cause the probable deformation. Further running the engine then increased the problem and eventual destruction.
Wasn't aiming to discredit you, but I don't see the shaft as being the problem but a symptom of an underlying cause. Was the event spontaneous or did it occur at a specific location during a pull? For instance were the HP/Trq curve climbing as the other runs then all of a sudden stopped climbing as previous pulls had become? Or did it occur after a run that was normal, then never pulled the same? I ask because the timing events may have dictated the cause of failure.
I'm doing a little digging on it because I would find it peculiar that the shaft itself would spontaneously become out of spec.

I'm not sure where this data comes from originally but it might become useful in this discussion. The original website is: http://www.rotaryeng.net/Rotar-v-Piston.html
http://www.rotaryeng.net/ROTOR_BEARING_LOADS.JPG
If we assume that to be an NA style 13B then I don't see the Turbo variations being order of magnitudes bigger (where the NA reads 170 kg/cm^2, the turbo will not read 1700 kg/cm^2).
It's not defensive. If I'm coming off accusatory I apologize, but I think the problem is before the bend of the shaft.

just cruising around and bumped into this thread. i am scratching my head as my friend Jose Le Duc runs RX8 cranks and he is making over 1000 rwhp. a couple of weeks ago he ran a 7.50 at around 180 mph. he leaves the line around 10,000 rpm.

hmmm.

hc

Well I must be wrong ....Hey Howard please use rx8 shafts in all your builds...Thanks

You guys can take it or leave it, the fact is I would not use an RX8 shaft in anything making real power......I would rather be safe than sorry.

I have had more sit downs with the actual mazda na engineers than most, I think i will stand by there data and Yawpower data than "my friend did it"

RX8 eShaft
 

I agree, imperical data is the only way to go with these issues. Drag cars typically rebuild more often than any road going car would. So in there case they don't care about longevity.

No, they don't care about longevity but the loads exerted on an e-shaft in a 1000 RWHP car (even one revving to 10,000+RPM) are going to be more than that of a 375 RWHP revving to 8,000. I still think something else may have contibuted to Glenns failure, what? Who knows.

I agree that imperical data is paramount, however, can't one argue that an 8 shaft has stood up to this amount of torque for so long and hasn't bent, be considered imperical? Regardless of the temper in the shaft and it being more prone to bending than a 13B shaft, that's still a hell of a lot of load.

Unless we're discussing royalty, it's 'empirical'. :)

More food for thought (or fuel for fire)

http://www.rotarycarclub.com/rotary_...1&d=1244861449

Where'd this figure come from and would you mind explaining?

I assume these are the forces on the stationary gear that would otherwise cause it to twist? How is this relevant to E-shaft loading? I'm just a genuinely curious lurker -- have no credentials for an opinion, and no data points to offer so feel free to ignore...

RX8 e-Shaft
 

You're just missing the point. But I think what we need here is more data. The more people that use the parts from the 8 in the 7 the more we can learn. My only thoughts here was whether longevity was an issue for you or not. So I for one would like to see some success with these parts. FD engine parts are becoming very expensive. The more parts the better. So let us know how succesful you are with this setup.

I agree more data is always good, but I think Glen has a very unique and valuable perspective here -- he actually broke one and followed up with Mazda to understand why and found something very interesting about tempering that has not been brought up before and should not be forgotten.

The facts I didn't know that I've gathered from this thread:
1) RX8 e-shaft is cheaper than RX7 one
2) RX8 e-shaft is lighter.
3) RX8 e-shaft was designed for a car that makes much less torque than the RX7 ever made.
4) Mazda does not temper the RX8 e-shaft, but does on the RX7 one.
5) An RX8 e-shaft has been broken by a prominant engine builder.
6) Tempering, as an extra step in manufacturing, inevitably adds cost.

Fact #5 proves that whatever was the particular failure mode experienced in Glen's build, in that particular instance the RX8 e-shaft was the weakest link.

Fact #6 brings into question the presumption that the RX8 eshaft is cheaper because its newer, as being cheaper because its cheaper to build actually makes more sense when it comes down to it IMHO.

Wikipedia has this to say about the process characteristics of tempering. Apologize if everybody already knows this, I personally did not:

1) Improves ductility and toughness
2) Reduces cracking
3) Improves machinability
4) Increases impact resistance
5) Improves malleability

#4 seems especially like something that might be good for anything inside an internal combustion engine.

It's from an ASE article regarding the 13B engine from an FD. Loads exerted on the stationary gear play a very large role in an asymmetric loading of the eccentric shaft. Since the loading appears to be greater than what the eccentric shaft sees on the bearing load. This means that a majority of the deforming load applied to the stationary gear should see abnormal wear when you have a case similar to Glenns. This is assuming that an abnormal ignition event caused the initial deformation of the shaft.

The actual title of paper is "Recent Technology Development of High-Powered Rotary Engine at Mazda" by Takumi Muroki.

It also has an interesting portion about timing and the propogation of the flame front depending on the location of ignition (10* EW TDC, 20* EW TDC, 30* EW TDC).

I figured it must have been from SAE -- I wish those papers were cheaper than $15 an article. Thanks for sharing and attempting to accomodate a newbie, but I think I'll still need to read the full text to really understand whats being said here. :-)

I swear I have portions of dyslexia or something, I screw up so many acronyms.

Not to discount Glen’s findings as I respect his knowledge and personal experience, but seeing how my name was brought up I figured I should respond.

The RX8 shaft has been in my car since March of 08 and has consistently been spun to 9k RPM and seen above 300 lbs rwtrq. We pulled the motor apart a few months ago to try out the ALS apex seals and the front and rear stationary gears show no signs of wear and the shaft is still like new. As a mater of fact, most of the bearing babit was still there. I would estimate at that time the motor had close to 30 races on it and around 400 street miles. Now the motor has around 40 races on it and another 600 street miles and is still going strong. At the most resent ProSolo we gave last years National Champion in a 500+ rwhp, single turbo, 3 rotor a good run for the money.

I have plans at the end of this race season to drop this motor in my street car and build a new one for the race car. The new build will be using the RX8 eccentric shaft along with a few other tricks to reduce the rotating mass. Time will tell, but at this point I see no reason to go back to an REW e-shaft.

Dan

when you guys use the rx8 eccentrics do you also get your rotors lightened as well or do you just swap eccentrics?
I am rebuilding my engine in November just to freshen it up. Its reading 15psi vac right now and i would like to rebuild it and i am interested in the rx8 eccentric.

Back up top! I'm going to be using the rx8 e-shaft in my newest build and I'm just wondering if anyone has any updates. I respect ALL opinions in this thread but am always open for more data or experience.

enough said, from an accurate source... rx8 e shaft for the win.. it is tapered too :) anybody know how good that is?

what class did you run ?

We run the car in SSM.

I have the Rx-8 shaft in my Rx-4's engine along with the Rx-8 stat gears and bearings. This is an NA setup mind you so I'm not really pushing these parts to their limits. I've got probably around 6000 miles on this engine with no problems of any kind. Runs great, still builds good power and wicked oil pressure. I don't know if there is any real significant gain to going with the 8 shaft, but lighter is lighter and cheaper is cheaper...... Those were good enough reasons for me.