MarkJ

Hello out there!

First time here. As a long time Mazda technician, I have some questions I
hope some of you can shed some light on. It revolves around the new internals
of the RX8. I have all the internal parts sitting on my bench, and am missing
some of the details that others have been talking about. I have weighed
the rotors, at 4.235 kg, they are not terribly light, compared to the race 20b ones.
The counter weights are indeed thinner, but actual weights are similar.
What is very curious are the stationary gears, now i might be missing something,
but I cannot fiqure out what is different. They are, to my eyes, identical to the
old 13b ones found in the gsl-se. I have a set of original Mazda factory
race gears, and other that the race modifications done to the rear gear, can
spot no difference. So why are the renesis gears given a different part number?
These gears also look to not have been hardened nor grooved and installed
with a multi window bearing like the twin turbo ones, anyone know why?

Also, what is so different about the e- shaft? Dimensions look to be the same
as the past ones.

Anyways, any light which can be shed would be appreciated.

Thanks, Mark


( I will save talking about the rotors for later)

Mr M

Rotor weight reduction compared to the 3rd gen RX7 was stated by MC as 11%, or about 300g. The ribs inside the rotor are thinner.

The flywheel is 20% lighter.

The stationary gears are cut slightly differntly for noise reduction. From memory the sides of the teeth (the meshing area) on the Renesis are slightly rounder than the 3rd gen. Or flatter, it is 2 years since I compared them. No idea about the bearing.

E-shaft dimensions are the same, it is supposed to be stronger and lighter (more holes in rotor bearing area).

Hope this helps.

MarkJ

Hi,


As to the gears, the stationary gear tooth profile is identical to all previous ones.
The only machined difference between the two, are the renesis looks to have a
deburring procedure at the very tip of the gear tooth. Has anyone run renesis
rotors on old style gears/ shaft?

Why has Mazda decided not to groove either front or rear gears and not installed
a multi window main bearings? Does this mean that they have eliminated shaft
flex at high rpm? I kind of doubt it. A good example is the race three rotor, not the
failure prone cosmo version , which still uses grooved window bearings, but has lighter rotors and rotor bearing journals which are 1.00 mm larger on the od.

Also as a side note are the rotor gears now hardened? By appearance, it looks
grey where all the others are shiney. Is this a coating?

Thanks, Mark

Charles R. Hill

iTrader: (7)

Mark,

The bigger question, since you have the engine apart, is just how similar the parts you see before you are similar to the performance versions of the same. This testimony will give the rest of us a much-needed break from the cynical naysayers who have told us for months that the Renesis is weaker than previous versions of the rotary. I have disagreed but that was only on a philosophical and historical basis rather than engineering or visual inspection. If you can give us your interpretaion on the comaprison of the seals, rotors, shaft, housing, and etcetera, that would be a great help as to the ultimate performance levels the Renesis is capable of. Thanks in advance.

Charles

red_rx8_red_int

Pics would be usefull also.

Charles R. Hill

iTrader: (7)

Oops, I forgot we are a visually-driven culture. Sorry.

Charles

MarkJ

Hi,

I have heard alot about the increased strength of the eccentric shaft, I'll have to
say its not, as dimensionally it is identical, material is also the same. Mazda has
only increased rpm limit to 9000. At this level things are just starting to get
interesting.
Shaft flex will always be the limiting factor. That is why the factory came up with
All the race proven procedures to help the engines reach their power / rpm limits reliably. If you think along these lines, than the twin turbo was indeed capable of more power. As to the renesis being weaker, I think its just a different animal. Its
purpose is not ultimate power. Because of the side port intake and exhaust, it will never exceed the power levels obtained by the peripheral design.
But I really like the rotor design, and will be using them in several race engines
soon. First, I will need to have a complete grasp of what Mazda has done with the renesis.
Again, anyone with some ideas, lets hear em!

Thanks

robertdot

Why would that be true?

MarkJ

The restrictive nature of the port design limits potential horse power levels. If you compare
known horse power levels with existing four port engines, normally aspirated of course, with those of peripheral port race engines. There is no comparision.
The renesis engine was designed to improve fuel economy, reduce emissions and create an acceptable level of power. They did this by reduceing the intake charge dilution that
occurs with a peripheral exhaust port.
Unless someone out there is working on getting a 13b to rev into gods country, a
peripheral port design will make more power than a side port.

Now that we have access to higher compresion rotors a peripheral port will now see
a significant increase in power.

wakeech

yes, it's just completely an issue of flow and efficiency, p-ports will always make more power than side ports at high rpm levels.

i'm still wondering what would happen with a perhipheral intake port and side exhaust ports, might be really neat.

CERAMICSEAL

I was thinking small bridge with side exhaust. It may create a slightly better behaved bridge port. However, having spoken to one wiser than myself, it was pointed out that although this may work it is limited by the lack of overlap (yes the same evil overlap that your getting rid of by using side-port in the first place.)
since the overlap allows you the scavenging effect. This is probably why there is very little horsepower to be gained through exhaust tuning on a renesis.

86rx7

Mark J can you confirm that the Renn shaft is dimensonally the same as previous 13b shafts? I heard they the oil groove on the front main bearing journal is moved slightly fore or aft (cant remember) compared to previous shafts.

shelleys_man_06

What would be the benefit of moving the oil groove?

I sort of understand wakeech's idea of utilizing a p-port while keeping the side exhaust. Using an intake peripheral port, you can have the maximum inlet flow area without compromising the corner seals. Keeping the side exhaust port, and not having to resort to a p-port, the engine won't have to scavenge some of the waste back into the intake stroke. It's all clean and simple. And on the plus side, I am sure you can safely put on the boost. But, what about idle and low speed driveability? Is a lopey idle an unchangable characteristic of having a p-ported rotary?

MarkJ

If someone wants to foot the bill, I can have an RX8 rotor housing
modified with a peripheral intake port that uses the same port timing
as the comp. housings. Cost, 700$CDN not including the housing.
Intersting to see the results, anyone game?

rxturbo

Hello,

Long time since ive posted but been very busy,

The stat gears on the rx8 motor may look the same but there is one thing different and part numbers and other items help to prove this... That is they are directional to the rotors, meaning you have to use the specific front rotor for the front stat gear and the rear for the rear, hence this is the slight burring on the tips of the teeth on the rotor gears and stat gears. think of it like this you cant grab a front rotor and stick it on the rear because the rotor edge cutouts and groove for the exhaust port would be on the wrong side... Its always better to have photos

With the crank well it is lighter as we have weighed it and it has more meat taken out of the rotor bearing area, also the journal down the shaft is bigger hence the front bolt is now bigger and like with the old shaft were you would have to get the bearing surfaces clearanced to suit racing, the rx8 shaft already has great clearances to suit and mazda offer different sizes of rotor bearing clearances.

And you cant compare renesis shaft and bearing clearances to MFR 13g engines especially crank flex we have got 4 of them here and 2 of them MFR specials and beleive me put them on some v blocks and a dial gauge and dont be suprised with the amount of throw out it can be scary, thats why thay run bigger clearance in the 13G especially the centre bearing, but the drag guys over seas have fixed this by tighting the front bolt to 300lbs fuuny but true..

Thanks

Rxturbo

CERAMICSEAL

Hey, hows it going rxturbo? How are your projects coming along? MarkJ is doing some similar things to you:peripheral with renesis and the 'right' seal material.
Have you found a solution to the side seal clearance thing? Nice to see you on here.

rxturbo

hello again

I know its been a long time

Well if you remember my old post I have already told everyone about the success of the PP intake and exhaust ports with stock internals rx8..

We have fixed the side seal problem and are now offering the modifcation to everyone along with the other great things we do..I dont really want to say how we have done it yet as it would not be fair to the owners of some of the race motors down here that we have had the mods done.. But the last motor we did was about $10,000 AUD just for the engine alone..
But we now offer all the mods as we have finished the R&D and are ready to have some fun!!!!!!!!

See you around, Iam going to try stay around this time

MarkJ

RXturbo, thanks for the message. The difference of the stationary gears still puzzles me,
I have measured both gears on a co-ordinate table, and have not seen differences in tooth profile. If this directionality is correct, I will need to make a center gear to fit the three rotor. The front gear looks to have the material to accomlish this. Frankly, I am getting tired of throwing time and money down the drain. Have you modified a front gear to fit the center housing yet? Also, how have the gears stood up?
I will assume that you are grooving the gears and relieving the inside rear of the
rear stationary gear. Anyways, thanks again!

rxturbo

Mark,

We have not done any centre plate mods as yet but it might be something that we will try on our shortened 20B engines which a ser6 centre plate instead of the big 20B one this also help that crank flex I was mentioning, With the stat gears we do all the race prep stuff, I dont what gears are offered in USA but the gears we get here are already grooved with ser6 style bearing in them, but as Ive seen there has been a lot of difference between the two countries with a lot of motors including ser 6 and 5, especially 6 port efi motors which you guys had in the GSL SE rx7 gen 1.... But again photos will show it better.

Thanks

MarkJ

Hi ,
Rx8 stationary gears here are not grooved, front nor rear, have the small tang for location of the bearing and do not use the multi window bearing either. Almost identical to the
early 13b stationary gears, with the exception of the increased size of the front thrust
bearings. Not at all like the twin turbo RX7. I can send pitures if required.
Are you using the short crank three rotor with success? Isnt that with the welded stationary gear? No issues with the set up? How many hours ? How are you getting oil to the bearing?
Also as to the side seal question, any further info on longer seals?

MarkJ

Hello again,

Looks like I might have a source for side seals. I will need to have a large number made in order to offset tooling costs. So far this looks to be the best way to go. I had contemplated machining the rotors for a larger corner seal, one way to eliminate the clearance Mazda designed for the Renesis, but have never liked to machine rotors. For one, it is extremely difficult to accurately set up the rotor. From the factory is usually best, but I have seen some bad new rotors. The Renesis rotors are machined the best to date. So I'd prefer to leave the rotor alone.
So does anyone need some longer side seals?

shelleys_man_06

What if I wanted to machine the RENESIS rotor to drop the compression ratio? I want to be able to support a substantial amount of boost using pump gas.

What are the advantages/disadvantages of a longer side seal?

MarkJ

Hi Shellys man, Renesis rotors do not have significant enough material in the recess to
drop cr enough for major boost. Longer side seals are intended to eliminate the
excessive clearance found in Renesis rotors so they can be used in engines with peripheral exhaust ports.

shelleys_man_06

MarkJ, are you implying we are stuck with the 10:1 CR? I'm probably sure I can get away with 12+ psi with the stock rotors.

What are the effects of a longer side seal with a side-exhaust port?

MarkJ

The side seal clearance on the RX8 looks to have been done by Mazda on purpose.
As the rotor crosses the exhaust port the exhaust gas would be trapped between the
outer oil control ring and the side seal corner seal area. In the old days practically zero
side seal to corner seal clearance was the hot set up. When Mazda adopted the side exhaust they had to prevent this blowby. Mazda had added a third oil ring to prevent the
gases from getting into the crankcase, and shortened the side seal to purge this gas.
But this is why you hear complaints of oil in the intake and hard starting/flooding problems.