farberio

iTrader: (7)

And? Aaroncake runs 400hp on a N/A transmission yet you don't see a legion of people saying n/a transmissions are as strong as TII transmissions.

I am not saying the RX-8 Eshaft is weaker. I am saying its conceivable that it is. Without testing you cannot prove it one way or the other. All you have is a set of examples that suggest one thing, not a set of testing that proves it.

My point is, if you happen to reside in the camp that says the RX8 shaft is weak you have no data to back it up. And if you reside in the camp that says the RX8 is just as strong you still have no data to back it up.


If it makes you feel any better I intended to use an RX8 shaft and actually purchased one, but after consulting with the person who was going to balance my engine I decided not to. It seemed that the balancing was likely going to add weight to the counterweights thus moving the weight loss from the RX8 eshaft to the counterweights. And since the counterweights are farther away from the center of rotation it would actually make a total negative impact. I never followed up with people that have had their assembly balanced on RX8 eshafts to confirm this but the person that balanced my engine has plenty of experience.

j9fd3s

iTrader: (3)

search n00b!

https://www.rx7club.com/showpost.php...4&postcount=49


Out of curiosity I hardness tested an RX8 crank and an FD crank.

RX8 journal = 60 Rockwell C
FD journal = 58 Rockwell C

RX8 center = 22 Rockwell C
FD center = 12 Rockwell C

22 Rockwell is about the hardness of 4340 so I think it's safe to say the RX8 item is made from better parent metal, and therefore probably less likely to 'whip' at high rpm.

Remember the Renesis engine is designed to rev higher than previous 13B's so one would assume Mazda allowed for this.

SoloII///M

iTrader: (13)

Wow. Just wow.

Pot / kettle?

rotordad

^ I wasn't aware that I was turning in an English paper. I guess he needed to take his own advice.

FC_fan

iTrader: (2)

um, I'm no pro but all I see in this thread is use which ever one you want.lol. Does it really matter? there are plenty of 85-91 turbo motors pushing 400, 500, 600 whp and they seem to have done the job with their e-shafts. you know, they have got the job done up till the rx-8 debuted. I'm just saying, if you can't prove either side then just use the cheaper GOOD solution. OP, if your 115k mile shaft checks good and isn't close to the wear limit then save the money from the rx-8 shaft and use it to have your current assembly balanced. you may not think it needs it but it can make your motor last a bit longer, especially if its seeing high rpms a lot and some decent boost levels.

No, I don't have personal experience with the subject. I just read a lot and listen to the pros and see what works for people over the years. this flame war doesn't make sense because there is no info to support it so just let it go guys. its not like one shaft will make the motor last forever, it's a rotary. you'll be rebuilding again down the road no matter how you look at it.

farberio

iTrader: (7)

I don't care enough to search, but this is some good information. By the looks of it you can tell one of the two camps to shove it.

ultimatejay

iTrader: (1)

[No, I don't have personal experience with the subject. I just read a lot and listen to the pros and see what works for people over the years. this flame war doesn't make sense because there is no info to support it so just let it go guys. its not like one shaft will make the motor last forever, it's a rotary. you'll be rebuilding again down the road no matter how you look at it.[/QUOTE]

Ummm, you obviously don't read enough because there is proof. See a couple posts above yours. The RX8 shaft has better/stronger metal. You can't beat the price. I wouldn't trust a 100k mile e shaft regardless of what kind, too much wear and tear on the shaft even if it specs out. Why not just buy the 200 dollar brand new RX8 shaft and call it a day?

diabolical1

iTrader: (3)

i think this is officially on par with the "2 mm vs. 3 mm" and "synthetic vs. non-synthetic" arguments - utterly pointless! (but with at least a chance for resolution). i'm sure for every handful of broken Renesis shafts people produce, there will be an equal amount of broken pre-Renesis shafts out there - whether they become common knowledge or not. use what makes you comfortable. i think 7+ years in production and the fact that there are a lot of Rx-8 owners out there abusing the hell out of their engines, with and without forced induction says that if the Renesis shafts were THAT problematic, it would have been common knowledge by now.

aside from the hardness numbers furnished by j9fd3s, i don't think i've come across any quantitative data - though i admit i honestly haven't been looking. however, the few broken Renesis shafts i've heard about are not enough to make me condemn them as weaker. it simply doesn't make sense to me. if i found myself needing a shaft, and i didn't have any on hand in my garage, i wouldn't think twice about buying a brand new Rx-8 shaft to build with.

it also makes sense that for every one like me, that is not disuaded, there's someone that is. so why don't you all just agree to disagree until such a time when there is actual proof, one way or another?

j9fd3s

iTrader: (3)

i posted this in the other thread, but really we're looking at 3-4 broken shafts out of 50,000 plus

scathcart

That's not true. Rotating mass balance is based entirely on the weight of the rotors, the eccentricity of the shaft, and the distance between the rotors and counterweights.
Changing to the RX-8 e-shaft doesn't change any of these factors, so you do not need to rebalance if all you change is the shaft.

scathcart

Proof, from Rotary Engine.

nycgps

iTrader: (4)

try it, then get back to me.

PnoyRx7

iTrader: (3)

then were going to have another pointless thread about " my dang motor dun gon bust, what do nao?" lol . i would get it balanced, i know its not the same but i figure its sort of like the rims/tires on the car, if you change the rims or tires you have to get it rebalanced(not if its a FC E-shaft, but since your going to a completely different car and the way the engine was designed), i couldnt think of anything else so correct me if im wrong lol.

farberio

iTrader: (7)

This looks kind of simplified, do you think that at the time of that book the mass of the eccentric shaft was nonexistent?

wvumtnbkr

Hardness does not equal strength!

Also, you can't tell what metal something is made out of by it's hardness (to a point). You can eliminate some metals with the hardness, but not pinpoint what metal it is.

scathcart

Done.
A long time ago.

scathcart

Your analogy is flawed.
If you take a balanced e-shaft from one engine and put it in another, you don't need to re-balance the e-shaft.
If you take balanced tires and rims from one car, and put them on another car, you don't need to get them rebalanced.

scathcart

Simple equation doesn't mean that it must be wrong.

Balancing of the eccentric shaft is done indepedently from the rotating assembly. First you balance the shafts, then balance and weight match the rotors, mock up bob weights and mount them to the shaft, and then balance the bob weights to match the rotor weights. Eccentric shaft lobe mass is not a part of the balance assembly.

Try it. Take your balanced rotating assembly, put it on a new e-shaft, and the balance remains the same. Been there, done that, too.

PnoyRx7

iTrader: (3)

i ment to take the rims off of the rubber lol, and even so , if you dont rebalance them when putting rims on a different car without touching anything, ive had people come back to the shop and say, my steering feels bad, and sure enough the rim was misbalanced

scathcart

Getting completely off topic, but taking a tire/rim combo off of a car and remounting it does not change the balance of the rim/tire combo. The position of the tire on the rim does not change, and neither does the position of the balance weights.

tuscanidream

iTrader: (6)

I've replaced tons of rear tires on my ninjas and I am yet to rebalance any wheel. And it has seen speeds no FC has seen before lol The rim is balanced, regardless of the tire on it.

So +1 to the above.

john ward

iTrader: (7)

I dont see how this relates but changing a tire on a wheel the balance definately changes.

10thAEWHiteHeat

iTrader: (4)

wow, you would think that a non-noob, non-mindless topic would be exempt from the usual e-dick measuring and useless banter.. shame on me for getting my hopes up. Anyway, thanks to all those who have made useful contributions to this thread.

I never did get a PM concerning the SUPER SECRET MAZDA HEAT TREATMENT OMFG lol. Cant say that part surprises me though.

Back on topic... Will the fact that I am using different rotors and housings than those designed for a Renesis when balancing? Or do i need to balance? Still confused as to whether that is gonna be necessary or not. Would I need to balance either way because of different rotors and housings?

j9fd3s

iTrader: (3)

the housings don't matter at all to the balance they do not move.

if you have a matched set of rotors and weights, IE a set from the same engine, you can use that no problem. or if you buy new, no problem

but if you're mixing parts, i'd balance it. a rotor made in 1989 won't be the same weight as a rotor made in 2009, even if its the same part number.

balancing is cheap!

i sent mine to glen at AZ rotary rockets, actually, and its smooth as glass.

D Walker

iTrader: (1)

I would balance, and I wouldnot give any other advice.
However, as very broad-stroke rules-
Swapping e-shafts between rotor sets is usually not an issue.
Rotors "sets", meaning the same weight, have not given me any issue with an 8500rpm redline. Anything over that and its time to balance, no exception.

Also, I know of rx8 shafts in 900+hp engines, so I would have no fears of it in a street car.