So my motor is about done being pieced together. I say "pieced" because it is a Frankenstein motor with different generation pieces that my tuner and I felt best to build for my purposes. The motor is being built to handle up to 600 whp one day if i please, but will only see 350whp for the near future. He recommended to use an Rx-8 E-shaft, stating that it was one of the better advancements in the Rotary with the 8. Does anyone have feedback on this or have gone with an Rx-8 e-shaft in their setup?

 

is it even the same length ?

I have an S1 8, I took The shaft out couple of times and its a Carbon fiber shaft, S2 Rx-8 have different shaft in a multi piece design. S1 is 1 piece.

dunno if it will bolt up to the FC tho, it should be different.

 

Eccentric shaft, not drive shaft.

To OP, there are some minor differences, but none that are extremely significant that would really warrant replacing a perfectly fine piece. They are mainly used as a cheap alternative to purchasing a brand new S4/5/6 shaft.

 

From my research, although the Renesis e-shaft is lighter, its mainly used in RX-7 motors because its cheaper. Its not a drop in mod too, you have to mess with the oiling.

 

Its a little lighter, but is it worth it? IMHO, no. Stick with the rx7 e-shafts.

 

I have one here now that we are using in an FD rebuild and its a really nice piece. Its not a little lighter, its a full pound lighter, and I think it is worth it considering the price, its brand new, and its lighter. Its also lighter in the right place, the shaft itself rather than the rotor, so you lighten the assembly without losing any of the flywheel effect seen when you use superlight rotors.

 

A pound lighter of rotating mass is great and all, but its so close to the central pivoting axis that its negligible.

 

^thank you.

 

No, it is not negligible, but it is in the best location for a street RX7. When you lighten the rotors it hurts the flywheel effect the rotors have on the low end, which is why lightened rotors ina street car are just not a good idea. On the other hand, a pound out of the rotating mass where it hurts nothing is well worth it in a street car. Even in some race cars its well worth the upgrade. Keep in mind that we used to have to pay for lightening up the e-shaft, and if you lighten the rotors you have to have them balanced, which again is money spent. The low cost and fact that it is an OEM part and works perfectly is what makes it "worth it"

 

Rx-8 Eshaft has a reputation for being weaker than the eshaft on previous rotaries. I wouldn't put it in a boosted application when a perfectly good 13B eshaft is easily available.

 

My 10k mile, 100+ dyno pulls, 405rwhp RX8 e-shaft disagrees with you. I pulled the engine apart a few weeks ago and there was virtually zero wear on shaft, main bearings, or rotor bearings.

 

His car is not a race car, therefore the benefits are negligible and not worth it. You say that that it won't hurt the 'flywheel effect' by removing mass from the middle. Thats not because its a better place to remove it from, its because removing the weight there doesn't do much of anything! Spending extra money to buy a RX8 eshaft is not worth it, if you have to replace yours anyway and for some strange reason you have to buy new then by all means go for it.

 

What EXTRA MONEY???? Are you not aware that the RX8 e-shaft is $186.75 RETAIL from Atkins? Are you also not aware that e-shafts need to be replaced from time to time because they are worn out, bent, or otherwise not useable? Or are you one of those that just ASSumes the e-shaft is good because it looks shiny and smooth? If you are building a STREET car engine and have the slightest doubt about the e-shaft just buy a new one, its cheap insurance against having an issue later, especially if I am already replacing rotor and stat gear bearings. Oh, and use the RX8 stat gear bearings too, as they are a multi-window bearing.
A race car will benefit from this yeap, thats true, but a street car benefits as much, and pays nothing in return. It is a better place to remove the weight from the center because it IS rotating mass and DOES help but you are not giving up enough low-end torque to matter.
Which is probably why Mazda reduced the weight in the first place rather than just leave the shaft as it has been since 1985.

 

Did the say his was bent/broken/unusable? I didn't read it, which means the OP will be spending an additional $186.75 RETAIL for something he doesn't need and something that does not supply $186.75 RETAIL of benefits.

Also, a used and usable FC eshaft can be had on the forums for way less then $186.75 RETAIL. Which is why I said the RX8 is a good choice IFF you are buying new.

 

oh **** I didn't know what I was thinking.


the E-shaft works, but you need to rebalance the whole rotating assembly. includes the rotor that you want to use and the correct front & rear counter weight of the engine you're running.

the biggest difference between the MSP e-shaft over the previous are :

- 4 holes at the center so it's 0.6 lbs lighter. (older ones have 3 holes)
- has extra clearance ground into the rear half of the rear main bearing journal.
- should have better metallurgy
- its "much" cheaper.

if I let my FC sits for more than a week it smokes like it caught on fire, almost time for a rebuild I guess, and when Im rebuilding, I will use MSP's E-Shaft for sure.

 

Are you running the RA OMP adapter?

 

As with TT there are a few guys I have spoken with that use the RX8 shaft with success. If you are doing a build why not take advantage of the RX8 shaft benifits. New for new the RX8 shaft is cheaper, but if you are set on used of course you will find the prices lower.

 

That is the point I was making regarding why the RX-8 e-shaft is used as a new replacement rather than a 13b e-shaft prior to the Renesis.

I've already given up in this thread advocating the point that the weight of the RX-8 shaft is only marginally beneficial in this thread due to its location.

For those who may search and find this thread in the future: my opinion hasn't changed, I've just made all the points I've got for this argument so I'm retiring for now. For reference, Google "moment of inertia." Basically, the force exerted in the rotational direction is equal to the force in the cross direction times the distance from the pivoting axis.
Example: 10 newtons times 10 meters is a much greater force exerted around a pivoting axis than 10 newtons times 5 meters.
An example for this situation: A 10 pound eccentric shaft so close to the central axis exerts a moment of inertia very similar to a 9.5 pound eccentric shaft the same diameter. (The weight of the shafts is arbitrary in my example, I don't remember their actual weights).

 

I guess most people know that 0.6 lbs of savings are meaningless.

but the point is that, lots of people, including me, would rather pay 180 for a brand new part + pay extra to balance it than trying to get some used parts from people you don't know.

of course if your e-shaft is usable then yes you can reuse it, but lots of people (including me) would rather get the latest + balance and stop worrying about what happens if I re-use the e-shaft, even it might seem ok.

 

Not meaningless, its not worth it. Meaning if you have a usable e-shaft then the cost of going to the RX-8 eshaft does not justify the .6 lbs. If that .6 lbs was spinning 10 feet away from the center of rotation then that would be awesome. But since its .6lbs on the center of rotation the benefits are not as great.

Congrats. Some people don't have an extra $500 to buy a new e-shaft and get their rotating assembly balanced.

Of course what do I know, I rebuilt my engine with used (and free)rotors, used seals, used counterweights form a different set of rotors, used housings, used and severely pitted irons and a used eshaft.

 

for street, I guess not, for race, anything helps.


if you want something that last. why not spend the money and do it right in the first place ?

everybody has a different point of view, for me, I rather just spend some extra money, get the latest and greatest, and be done with it.

This is also the reason why I just ordered a set of Ceramic seals from NRS.

Is it worth it? for me it is. the set of seal worth more than what I paid for the car.

 

Not going to argue the positives of weight from one over the other, but there must have been a reason in which why Mazda did it right! I noticed in the post above the words (similar, close & basically) were used, now that just tells me that there is a difference. While it may not be a dramatic difference, it still is.

 

Nobody is debating that it does make a difference though.

 

the rx8 shaft lacks the heat treat process' that the other shafts come with from mazda, i would highly suggest NOT using it as i have seen several break causing catastrophic engine failure and damage.

 

You have some proof of that? I find it hard to believe Mazda would put an untreated shaft in an engine where they put in hardened stat gears, multi window bearings, etc. Also, I find nothing in any of my factory documentation showing lack of anything except weight.
Show me the tech.