Official: rx8 e-shaft thread
09-17-08, 10:13 AM
#1
He who smokes bitches
Thread Starter
Official: rx8 e-shaft thread
I've seen a lot of buzz lately about using an rx-8 e-shaft in the older n/a (s5 6 port is what I'm interested in the most) engines, but who has actually done it?
What were your results?
What did you actually have to do to make it work?
Is this really a mod worth doing? Or is it all hype?
Any input is appreciated.
What were your results?
What did you actually have to do to make it work?
Is this really a mod worth doing? Or is it all hype?
Any input is appreciated.
09-17-08, 05:29 PM
#2
Red Pill Dealer
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I would like to add to your question. Do you do the oil jet mod to the RX8 shaft like the 13b? Do the RX8 stat gears use the larger thrust bearing like the FD?
09-18-08, 11:36 AM
#4
Old [Sch|F]ool
It's a little lighter, and it's a LOT cheaper.
Or, it's a LOT cheaper, and it has a slight performance benefit as well.
Personally, I have about a zillion E-shafts lying around, but if I needed to buy a new one, and the cheapest one available worked, I'd go for that option.
Or, it's a LOT cheaper, and it has a slight performance benefit as well.
Personally, I have about a zillion E-shafts lying around, but if I needed to buy a new one, and the cheapest one available worked, I'd go for that option.
09-18-08, 12:30 PM
#6
He who smokes bitches
Thread Starter
so if you were rebuilding an engine but you did't necessarily NEED one, would it be worth putting in for performamce gains?
And is it a direct replacement?
And is it a direct replacement?
09-18-08, 04:54 PM
#7
Old [Sch|F]ool
I would imagine that it would require a rebalance, since part of what the counterweights are balancing against is the weight of the rotor throws, and some of the weight loss is coming from that area.
I'd concentrate on other areas first, IMO.
I'd concentrate on other areas first, IMO.
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09-18-08, 06:19 PM
#8
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If you were going to be looking for solely a performance gain and wanted to run the RX-8 e-shaft (since it is lighter and cheaper), you could consider running the RX-8 rotors, which are both higher compression and significantly lighter then S5 and S4 rotors (10.0:1 vs. 9.7:1 vs. 9.4:1) and (9.3 lbs vs. 9.54 lbs vs. 10.04 lbs respectively) Get ahold of the proper counterweights and it would be much easier then to get the assembly balanced. However, you may also need the stationary gears (I'm not 100% sure that the 13b and renesis stationary gear bearings are the same) Problem lies in that it's not advised to run the Renesis seals with our peripheral exhaust, since they are much shallower (4.5mm at thinnest point compared to 8 mm from the 13b) and much weaker. In order to accommodate regular 13b seals, you would need to mill it. Not cheap or easy by any means...
09-18-08, 06:48 PM
#9
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the weight savings is nice, but put it in perspective, the whole rotating assembly is like 800oz (rotors, flywheel, cw's, seals, bolts etc etc), you're removing 8 of that. thats 1%.
is it better? yes. weather its worth it is up to you.
09-20-08, 07:19 AM
#11
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almost compatible but not.
My understand is that while the all the major dimensions of the 13B-MSP eccentric shaft match those of the 13B-REW e-shaft, the oil hole in the shaft for the main front bearing is about 4mm further forward on the RX8 item when compared to the RX7 item. This is due to a the difference in the thinkness of the front and rear plates on the RX8 engine when compare to the RX7 items.
I've never personal seen the two e-shaft layed side by side to confirm this, but that is my under standing of the difference between the two, over and above the reducted weight of the RX8 item.
I've never personal seen the two e-shaft layed side by side to confirm this, but that is my under standing of the difference between the two, over and above the reducted weight of the RX8 item.
Last edited by TAZ-NZ; 09-20-08 at 07:22 AM.
09-20-08, 09:13 AM
#13
There's an atricle in R C C digizine about using the RX8 shaft in REW engines. Really great info in the article.
Also gets into using the stat gears and bearings from the 8 as well.
A few minor differences, but all can be accounted for. And given the availability and price of the 8 parts, if you need these pieces for a rebuild - they are great useable options. If you want them as a performance provider - don't expect much.
Also gets into using the stat gears and bearings from the 8 as well.
A few minor differences, but all can be accounted for. And given the availability and price of the 8 parts, if you need these pieces for a rebuild - they are great useable options. If you want them as a performance provider - don't expect much.
09-21-08, 01:42 AM
#14
so I called mazdatrix about this and they said that I would need my rotating assembly balanced and it didn't matter if I was using s4 counterweights with s5 rotors since they would all need to be balanced together and weight would be removed from the counterweights to balance the rotating assembly
but pineapple racing had a different view (quoted from email)
"The shaft is interchangeable so just use the matching rotating assembly. The S5 rotors dictate the use of S5 balance weights/flywheel or rear counterweight. for a mild
application, factory balancing is ok. rob "
two very reliable sources conflicting responses
09-21-08, 12:12 PM
#15
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balancing is cheap....
09-23-08, 04:41 PM
#17
When I read your email I didnt realize you were referring to swapping in the rx8 e-shaft.
In that case we are still up in the air. While the lobes will be weighted differently than the S4 or S5 or FD shaft, that few ounces is still very close to the center line of the rotating assembly so will have very little impact. While it is possible that the balancing change is small enough to not be important, I cannot say for certain as I have not tested it yet. Probably at this point I would balance it to be on the safe side.
09-23-08, 10:09 PM
#18
Ah, you are the guy that emailed me the other day (azrotaryrockets)
When I read your email I didnt realize you were referring to swapping in the rx8 e-shaft.
In that case we are still up in the air. While the lobes will be weighted differently than the S4 or S5 or FD shaft, that few ounces is still very close to the center line of the rotating assembly so will have very little impact. While it is possible that the balancing change is small enough to not be important, I cannot say for certain as I have not tested it yet. Probably at this point I would balance it to be on the safe side.
When I read your email I didnt realize you were referring to swapping in the rx8 e-shaft.
In that case we are still up in the air. While the lobes will be weighted differently than the S4 or S5 or FD shaft, that few ounces is still very close to the center line of the rotating assembly so will have very little impact. While it is possible that the balancing change is small enough to not be important, I cannot say for certain as I have not tested it yet. Probably at this point I would balance it to be on the safe side.
) so now its basically gathering all the right. Although now I still need to figure out how balancing a rotary is different than a piston engine rotating assembly. I had read through the section in the competition catalog but I gotta ask my instructor if the shop is able to balance it.this may be a dumb question but would you balance them without any seals/springs in the rotor, or something like a naked rotor? Or do the dummy weights compensate for those?
Last edited by fidelity101; 09-23-08 at 10:23 PM.
09-25-08, 10:28 PM
#19
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well, I know that the earlier 13B shafts (pre '86) were interchangeable with all 86 - 95 13B shafts. Now, there's a few weight differences going on around there, because the pre '86 13B rotors weighed about 11.5 lbs, the 86-88's were about 10lbs. and the 89-95 rotors were all about 9.5lbs. I confirmed this with someone (can't remember who) from Mazdatrix about a year ago and it was basically stated that the shaft is balanced "itself" and is thus separate from the whole rotating assembly when it comes to balancing it. He followed up with saying that ALL 13B shafts from all years are interchangeable, even the RX8 shafts. You will also notice that there is only 1 shaft sold for 86-92, even though the rotors for 89-92 lost .5 lb.
BTW, I also asked why the 93-95 shaft was $46 more than the 86-92 shaft and he told me that it's because there is a slight taper that was added on the bearing journal (surface) for the rear stationary gear.......something that Mazda "added" in 93 and is also done to the RX8 shaft as well.
Brian
BTW, I also asked why the 93-95 shaft was $46 more than the 86-92 shaft and he told me that it's because there is a slight taper that was added on the bearing journal (surface) for the rear stationary gear.......something that Mazda "added" in 93 and is also done to the RX8 shaft as well.
Brian
09-30-08, 07:30 PM
#21
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The RX-8 e-shaft must be used with RX-8 stationary gear bearings and rotor bearings, the journal sizes are slightly different.
The RX-8 main journals have precisely .0001" of taper machined into the front and rear main journals. This is to prevent the journal from spinning a stationary bearing at high rpms when the shaft flexes. I measured mine myself with a Zeiss Contura CMM, it was as precision made as a NASCAR Cup engine crankshaft on dimensions, tollerances, and surface finish, it's uneconomical to get any better without a redesigned e-shaft.
Although the RX-8 e-shaft is lighter the weight lost is very close to the center of rotation. Thus it provides minimal gains in moment of inertia, but a gain none the less.
A reputable rotary company has told me that substituting the eshaft on an older rotary does not require rebalancing unless you are building a high output race engine, again the weight lost is near the center of rotation and the balance of the shaft is not much different from a stock unit on an older engine. Just make sure you use the appropriate counterweights for you're engine (S5 counterweights with S5 rotors, etc...)
Again the oil galley requires modification.
And of coarse it's cheap!!!
The RX-8 main journals have precisely .0001" of taper machined into the front and rear main journals. This is to prevent the journal from spinning a stationary bearing at high rpms when the shaft flexes. I measured mine myself with a Zeiss Contura CMM, it was as precision made as a NASCAR Cup engine crankshaft on dimensions, tollerances, and surface finish, it's uneconomical to get any better without a redesigned e-shaft.
Although the RX-8 e-shaft is lighter the weight lost is very close to the center of rotation. Thus it provides minimal gains in moment of inertia, but a gain none the less.
A reputable rotary company has told me that substituting the eshaft on an older rotary does not require rebalancing unless you are building a high output race engine, again the weight lost is near the center of rotation and the balance of the shaft is not much different from a stock unit on an older engine. Just make sure you use the appropriate counterweights for you're engine (S5 counterweights with S5 rotors, etc...)
Again the oil galley requires modification.
And of coarse it's cheap!!!
10-03-08, 06:22 PM
#23
There is some info that suggests that the Renesis e-shaft is weaker than the 13B shafts. There was one installed in an REW that ended up bending! It wasn't mine but I've got a theory and am going to test each shaft to see if it has any validity. I suspect that there is a hardness difference. Not due to material chosen but rather due to heat treating. We have many things heat treated at work for differing hardness levels and I have a couple of different hardness testers. Once I get my hands on both shafts, I'm going to test them each at various points to see if in fact this is the case. It makes sense but one test result is worth a thousand expert opinions! Until then I personally wouldn't use an RX-8 e-shaft.
10-03-08, 09:37 PM
#24
There is some info that suggests that the Renesis e-shaft is weaker than the 13B shafts. There was one installed in an REW that ended up bending! It wasn't mine but I've got a theory and am going to test each shaft to see if it has any validity. I suspect that there is a hardness difference. Not due to material chosen but rather due to heat treating. We have many things heat treated at work for differing hardness levels and I have a couple of different hardness testers. Once I get my hands on both shafts, I'm going to test them each at various points to see if in fact this is the case. It makes sense but one test result is worth a thousand expert opinions! Until then I personally wouldn't use an RX-8 e-shaft.
