Why not a 3-rotor?

[Signal 2]

Hopefully this isn't a repost......I admit I don't surf the net and read all the magazines like I used to, so maybe I've missed the answer to this somewhere from the "in-the-know" crowd....With all the talk of the "new" RX8 in another thread...and even newer RX9 I keep wondering.
MAZDA used the NA 3-rotor successfull AFAIK in race applications. I don't know much about it, but assume bringing it to the street in a de-tuned state for longevity shouldn't be a huge deal. In fact, I thought that was the ultimate reason for it's developement. I also understand CAFE and CARB concerns, but it seems like those could also be engineered around. I'm SO not an expert, but maybe playing with the compression on rotors, port sizes, bigger-badder cats, hotter spark.....whatever.
EVERYONE I've ever talked to, and every write-up on the RX8 I've seen has consistently praised it's beautiful handling but then some mention is then made about the low-torque characteristics. And as I understand it any type of forced induction to cure that is either not real productive on the Renesis, or not cost effective. Maybe the RX8 guys can educate me here though too?

 

[Old Rotor]

The reason there is not a three rotor is MPG.

 

[LordWorm]

The 3 rotor did make it into 1 production car iirc, and our fearless leader Antoine happens to own a very fine example of it, the Eunos Cosmo.

However, the largest problem with triple rotor engines is fuel economy. even the 13B isn't what you'd call an overly economic engine.

Hell, for not much extra production cost, they could very easilly build production 4 rotor engines (like what was in the le mans winning 787B) or even a never-before-attempted 5 rotor - but the cost of keeping such an power plant on the road would be unbelievable, so the 4 rotor stays on the track, and the dream machine 5 rotor stays in the dreams of rotor fans....

Will mazda ever revive the 20B and 26B? i really really hope so, and maybe with their hydrogen powered rotary engines that are insanely efficient, one day we will see these beasts back on the road - but i highly doubt they'd ever get one on the road in petrol form, not considering the kind of hoops they had to jump through to get the RENESIS to pass emissions specs.

20B and 26B may not solve the torque problem, rotary engines are not the torque monsters their pistons cousins are - which is why mazda started turbo charging the 13B in the first place (even the Eunos Cosmo 20B is turbo charged from the factory).

 

[speed1585]

I would love to see mazda develop a single/dual rotary with the current electric engine tech being used. I htink that would make for one hell of a powerplant.

 

[Roywhitep5]

5 city 10 hwy

 

[speed1585]

5 city 10 hwy

What is this for?

 

[JoseProte83]

Fuel consumption. Kinda exaggerated tough...

 

[speed1585]

lol i know its fuel cunsumptions. I was asking mpg for what vehicle?

 

[Signal 2]

One major reason the Renesis is a side-port exhaust is to eliminate overlap. That reduced emissions and increased fuel efficiency. Making a three-rotor would likely reduce mileage when compared to the two-rotor, but then a V8 generally isn't expected to get as good of mileage as a V6. You would however increase torque and horsepower which is what most of us enthusiasts want. Basically I don't think mileage is the major issue.
I've done a little reading since starting this thread. Together with all the other marketing concerns, I've come to suspect it might be mostly a packaging issue. A three-rotor just won't fit.

 

[Antoine]

Good thread topic (thumb)

My official answer is...I believe Mazda wants to get the most out of 2 rotors because...It's smaller...lighter and gets better mileage AND of increasing importance these days...produces less emissions.

All this is necessary for the mainstream market and buyer...which puts food on Mazda's table.


My unofficial answer is taken from a previous post of mine:

"Give me 3 rotors and two turbos any F'in DAY! (woowoo) (rockon)"

Although, I'm also a general Rotary fan...I dig the sound and feel of the Renesis/RX-8 and I love the sound of a NA PP Rotary...More power to Mazda if they can continue to increase performance with a 2 rotor while satisfying the increasing standards for mileage and emissions. (2thumbs)

 

[R2s99zoom]

biggest problem with going above 2 rotors is the design of the eccentric shaft. With more than 2 rotors, to assemble it all, the shaft cannot be a single piece to have the bearings and rotors fit properly... and for large production runs, having your driveshaft not being one solid piece is generally seen as a bad idea... escpecially when you have a motor that has the potential to spin up to 10k rpm

so, multi rotor setups are relegated to pure race engines, and limited production runs, such as antoine's cosmo.

i just finished reading this book:

https://www.amazon.com (commissions earned)

it has a section on multi rotor setups, and lots of cool cars we never got to see go into production, like the 4-rotor mid engine corvette, and lots of history on the many mazda rotaries

 

[Signal 2]

biggest problem with going above 2 rotors is the design of the eccentric shaft. With more than 2 rotors, to assemble it all, the shaft cannot be a single piece to have the bearings and rotors fit properly...

Interesting. I'd heard those issues raised for the 4-rotors, but wasn't sure if that applied to the 3-rotors since they developed them in race applications. Too bad. Thanks for the link.

 

[lil_red_wagon]

i am going 3 rotors in my t II later on and it won't have anything to do with mileage or longevity. i just want a sunday driver. if that is what you are going to do when you 3 rotor swap, go for it. i am not saying that it won't be reliable, but it won't be the best option for a regular driver. the 13b has a good compromise between longevity and power.

 

[Antoine]

biggest problem with going above 2 rotors is the design of the eccentric shaft. With more than 2 rotors, to assemble it all, the shaft cannot be a single piece to have the bearings and rotors fit properly... and for large production runs, having your driveshaft not being one solid piece is generally seen as a bad idea... escpecially when you have a motor that has the potential to spin up to 10k rpm

so, multi rotor setups are relegated to pure race engines, and limited production runs, such as antoine's cosmo.

i just finished reading this book:

https://www.amazon.com (commissions earned)

it has a section on multi rotor setups, and lots of cool cars we never got to see go into production, like the 4-rotor mid engine corvette, and lots of history on the many mazda rotaries

Another book I'll have to pick up..Nice find!

I did read somewhere that the 20Bs were basically hand-assembled and not "mass produced"...Which is why each 20B has a "20B MAZDA" plate/marking and stamped production/serial number (maybe even two markings...need to confirm)...This is a crappy pic of mine but you get the "picture"...

It's also interesting to note that the 20Bs were assembled in batches and not every "batch" was created equal...Here is a post from DMRH on another forum...He's the Eunos Cosmo/20B Guru and has recently joined Mazda Forums!

This is a basic way to understand your 20B engine

000 - 999 = 1st batch
A000-A999= 2nd batch
B000-B999= 3rd batch
C000-C999= 4th batch
D000-D999= 5th batch
E000-E999= 6th batch (only heard of these, never seen one)

Series-I = 1990-1993 (JCESE)
Series-2 = 1994-1995 (JCES)

1st batch 000 - 999 from cars JCESE-100031 - JCESE-100830

Suplus engines must have been "spares"

2nd batch A000 - A999 from cars JCESE-100831 - JCESE-101???

Never imported a Cosmo with a black manifold & we have done every year version from 1990 - 1995.

A-series motors (2nd batch) are ok, the shaft problem was no more for them.

Many of the first batch powered Cosmo's had engine failures under warranty. Even if the engine was suspect, it was changed. The dealership were under orders to crate the 20B back to the factory where a new engine would be sent back complete.

The dead ??? engines would be sent to the wreckers where back hand deals ment they found there way to the exporters & many early series motors came down under in the mid 90's. At one stage you could get a 20B for AUS$1800

High boost wasn't the problem with the early engines. It was the "snap torque". The engines would load up to 95% peak torque inside 1 second at a low 2000rpm. Thats what made them pop. Early engines with single turbo's running 15psi would be fine as they would have to rev to get that power. less lateral loading at 4000rpm+ you see.

Its almost always the centre rotor (as stated) that goes, been there, done that. Centre part of the shaft is the point of most flex.

I have seen the later C-series engines with the extra meat on the side plates. yet they seem to be as reliable as any other A-series plus engine.

Engines with the numbers ground off are factory re-built engines that have been used as warranty replacments to keep costs down. This was done later in the Cosmo run & not earlier.

So basically...The later C & D series 20Bs were made a bit "beefier" than the earlier versions.

Here's an interesting link from Mazda about the 20B...

http://www.mazda.com/mazdaspirit/rotary/story/p6.html


Another factor is cost...I believe when the Eunos Cosmo went on sale in Japan...If you chose the 20B over the 13b...You would have been paying a huge premium. No doubt the 20B was a very expensive option for the customer, it was also a very costly engine for Mazda to produce!

If you need to rebuild your 20B here in Japan...It will run you nearly $10,000 (U.S. beans) from a qualified Mazda Dealer...and that's only to factory specs...sans upgrades!

I suspect if you called on a well-known tuner shop to rebuild it...It would run about the same or even more with upgrades.

In the end...If you can pay...then you play with the 20B.

However...From my experience with the Cosmo so far...If you keep the 20B relatively stock and upgrade parts like the cooling & ignition system and perform routine maintenance...It can prove to be just as reliable if not more so than any other modern high-performance engine...and I bet you can rack up some serious miles with one before you need to rebuild...