RX8 E-shaft vs 13B-RE/REW shaft

[TitaniumTT]

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?

[hyperlitenerd]

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

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

[TitaniumTT]

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?

[hyperlitenerd]

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.

[Fidelity101]

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

[TitaniumTT]

Originally Posted by hyperlitenerd

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.

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.

[TitaniumTT]

Originally Posted by Fidelity101

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

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

[Prometheus]

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.

[TitaniumTT]

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.

[glenrx7]

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

[TitaniumTT]

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.

[glenrx7]

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.

[vex]

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:

One's one piece (OEM), and the other is actually 3 pieces (designed to eliminate e-shaft flex at higher rpms, which again, isn't really a concern unless you're building a race motor that will rev that high and is built to withstand the BLOCK flex you'll experience prior to having to worry about SHAFT flex).

This is for 20B engines, but I believe the principle is still applicable. Was the original engine Pinned or Doweled?

[TitaniumTT]

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.

[glenrx7]

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.