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.

[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.

[Fidelity101]

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

[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?

[glenrx7]

Originally Posted by 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:

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

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.

[glenrx7]

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.