Building a 3-rotor 13B, possible?
 

First, relax...I don't have the know how nor the metal working skills to build such a thing. That's not what I'm really talking about...

I'd rather have a NA engine than a Turbo or SC since it seems a NA rotary would last longer.

I know there is a company out there, I think in NJ, that builds 3-rotor engines. BUT, if you wanted to save money and build yourself a 3-rotor Renesis based engine what would you need to do?

I know the E-shaft (if I remember the right name) would have to be changed and suspect:

*some type of custom bracket/block to connect the new rotor
* a new header, intake manifold
*new ECU?
*motor mount?
*move some things around for space (maybe)?
*new tranny?
*new rear end?

As a newbie regarding the rotary and the details of engines overall, what would you have to do to build such a engine? I'm guessing this is not an easy task or else more people would be talking about it but to keep up with the Turbo & SC people another rotor would probably be the only real NA way.

I wish it was a matter of a new e-shaft and rotor housing but that's my wishful thinking.

Please be as detailed and technical as you want, I'm trying to learn here. Is my dream super far fetched or do you all think in time there will be an "easy build kit" for making our Renesis a 3-rotor?

Thanks in advance for the rotary wisdom! :wavey:

I think this engine would actually be considered a "20b" (which basially means it's a 2.0 litre engine, just as our 13b is a 1.3 litre engine!). But... I think the fact that our ports are built into the sides of the chambers rather than the periphery (or the "outer wall"), you'd have to use a middle rotor from an older engine? The eccentric shaft would need to be longer to fit through all three... and that's about all I could say. lol

This is something I'd seriously like to know as well. NA all the way. :)

btw once it's 3 rotor it is called 20B in Mazdaspeak....

edit: pwned by slowness :shocking:

^ :) I win!

If you were to try to do this with Renesis parts, you would still need to machine a new intermediate housing. The ports in the end-housings are bigger and different than the ports in the intermediate housing, so two intermediate housings would result in the middle rotor not getting enough air.

Of course, custom e-shaft, manifolds, etc. More cost effective to source a 20b. If you were to peripheral port it (both intake and exhaust), it would be easier as you wouldn't need two different intermediate housings.

Ohhhhhhhhh, thanks VectorWolf...you too ZoomZoomH, no "pwned" intended...lol

Thanks, I think I understand what you all are saying. But...I thought that the "side port" made the Renesis more efficient. Is that true? Since the Renesis is the most modern rotary engine we have I thought it would be better to start there.

What I would worry about with the 20B is that I would have to then change a whole lot of other things to make it work. Where do you get a tranny from, ECU, etc?

Teach me more...

the side intake/exhaust port is mainly designed to improve exhaust emissions of the rotary engine

to make *real* power, peripheral ports (both intake AND exhaust) are still the preferred design (see Sportbook ALMS prototype 20B race motor :D: )

By the way, can I go some place and buy a rotary engine (Renesis hopefully) model that I could take apart to see the guts of the engine. There is no better way to understand all of this than to see what I'm working with.

Is there a place online or a plastic Renesis engine you can build/take apart/etc so you can learn the details of it. Maybe Mazda would not allow such a thing...but it sure would help me learn more about the rotary engine.

Hmmmm....I wonder how much a Renesis engine taken out of a poor busted up RX8 from a junkyard cost. Hmmmm....

you can get a renesis motor from a couple places for around 2500 for a rebuilt one (3500 with out a core return) so I would thing you could get a damaged one for half that.

Thanks for the link, I just learned a bunch and I think I can see what you mean regarding adding another rotor. While...I still think it's possible and "MIGHT" be cheaper than a Turbo or SC...but what do I know.

I saw that I would need a new oil pan also if you added a rotor. I would love to learn how to work with metal.

By the way, the Renesis is built out of Iron right??? Why not a lighter metal? Too hot I guess?

The real 20b engine from the Cosmo saloon is a side-intake, perhipheral exhaust engine with 2 turbos. The Cosmo only came with an AT transmission, although the TII and FD transmissions can be adapted from what I understand.

The 20b will fit in the RX-8 and a couple people have done it, but say goodbye to your ABS/TSC/DCS. There are several aftermarket ECU's that can run a 3 rotor, and that's probably a better option than retaining the Cosmo ECU. Be warned; 20b engines are getting more rare and more expensive.

You can get a full peripheral port 20b from Mazdaspeed for $$$ or I bet Downing would sell you one for like 20 grand. The other option is to piece together a 3-rotor using 13b housings and one of the wider 20b intermediate housings. You'd still need intake, exhaust, and e-shaft, but its probably cheaper than a 20b if you know what you're doing.

As far as the side ports go, Mazda has used side intake and perhipheral exhaust on most of their motors before the Renesis. The true power applications use peripheral intake ports which make more high-end power, at the expense of idle and low end quality. And by high-end, I mean over 5k! Great for race motors, not for the street.

The new side exhaust ports on the Renesis result in the engine having zero overlap, which is actually quite beneficial for forced induction. The Renesis has basically increased 100 hp over the last 13b in NA form without any more displacement and a ten-fold decrease in emissions.

Acording to a post on here some where by Boostd7 (site owner) the next issue of Rxtuner will have an article on this very topic. Get the mag.

Acostia is the place you were talking about in NJ

A 3 rotor 13B is not really a 20B. It's a custom built engine, that happens to be approximately 2.0L. A 3 rotor MSP 13B is definately not a 20B.

Here's a custom 13B 3 rotor: http://www.hitman.hm/rx7.htm

Why do you lose all of the electrical stuff when switching engines?

The TCS/DSC are controlled by the ECU. I suppose you could leave the stock ECU hooked up and use something like an interceptor to fool it into thinking the stock engine is still hooked up, but I really doubt that would work. AFAIK, the ABS controller is integrated in the ECU also. The tach and speedo signals are from the ECU also I believe.

I had kicked around with RG what it would take to build a 3rotor Renesis engine from existing parts in the “cheapest” way possible. Bear in mind, the following is cheap only in the sense that I tried to use as few custom parts as possible. This is theoretically possible but not proven to work. Its also not the optimum design, but again, I was going for off the shelf parts.

First I would start with a 4port Renesis engine. I would then add another Renesis rotor and rotor housing. The tricky part is the second intermediate housing. I would get a 20B large intermediate housing and after filling in the extra seal grove area (and lapping it smooth) so it will mate up with the Renesis housings, I would make 2 custom side exhaust ports, one large and one small. This way the center rotor will breath and exhale the same as the out rotors. So your side exhaust ports would look like this.

“L” Rotor Housing “S” “S” Rotor Housing “L” “S” Rotor Housing “L”

Obviously, the most time, money an expense would have to go into this 20B intermediate housing. I think the side exhaust ports could be drilled out and made to work.

You could use a off the shelf 3 rotor eccentric shaft, but it would have to be rebalanced as the Renesis rotors weigh less. I would fab a simple box collector header (like the stock manifold) for the exhaust first, I know its not the best for flow, but the idea is cheap and getting the car to run. I would try to use the stock 20B intake manifold with some changes, if that doesn’t work, I’d create a simple manifold with 3 TB (one for each rotor). I would lose the stock oiling system and go pre-mix for simplicity. I would source a motec or a microtech for management duty.

All of this uses modified off the shelf parts. The real cost would be the work to the intermediate housing, balancing the eshaft and the manifold creation. This is not the optimum solution, the manifold design would not be optimal and you could argue that those smaller side exhaust ports are still hurting power.

This is a gross simplification, but I think in theory all this should work together.

The real cheapest way to get a 3-rotor Renesis is to wait until Mazda makes it. :)

Skip the three rotor and go for four. "Just" siamese two Renesis together front to back.

BTW, there is an old model kit in the "Visible" series of the rotary engine. Just google visible rotary.

Yeah that doesn't work too well. Check out granny's speed shop and their home-made 4-rotor from two 13b's that used a keyway and a tapered coupling to join the two e-shafts. It works, but it doesn't have the real smoothness since the rotors are spaced 180 degrees, unless you cant one of the engines 90 degrees. :Eyecrazy: You'd also HAVE to go peripheral port for that to work. They eventually determined it was too much trouble and went with a big Chevy motor.

Yeah, but all the talk regarding the Mazdaspeed 8 (if it EVER comes out) talks about Turbo or SC...or, the latest...wider rotors?

:0(

Thanks everyone for your comments, I learn a bunch here.

If I had the know how to work with metal (add rotary engines, engine management, etc lol), I would invest into figuring this out because 3-rotors just sound right to me.

Come on Mazda...heck, if you make it a 1L 3-rotor I think we all would be happy. 1L 325HP 3-rotor Renesis engine. Ohhh mama...

Where will rotary development go. If looking at formula 1 technology, I will think they must go with more rotors and maybe smaller or same as 13B size but not wider.
think of a peripheral port, what more can be done, I dont thing too much, just lighten everything, you cant get more mixture in (excluding turbos)
so why not go more rotors
wider maybe makes more torque, but ..... revs...power

If you look at the Mazda showcars, the rotary is going to be the powerplant for pure hybrids ie the internal combustion engine only runs the generator.

Think about it, they tune the rotary for maximum power to weight to efficiency. The only power that goes to the wheels comes from an electric motor. The cure for the rotary torque issue. Infinite torque at 0 RPMs.

This is completely wrong. Passenger cars are quite a world away from Formula 1. Obviously having more combustion chambers per a set amount of displacement yields better efficiency, but at the expense of added complexity and cost. Look at the F22C versus the LS7 engines. The F22 is getting near 120 hp / L, while the LS7 is more like 70 hp / L, but the LS7 is not all that much bigger or heavier while making twice the hp.

If what you were saying was true, we should all be riding around in 14 cylinder 2L engines. They probably would sound wicked, but it would be hard to justify the complexity and cost. The wider rotor width IS a good idea; the resulting engine will make at least as much torque and hp, all at a lower RPM. And we all know that even if torque drops off, hp is still increasing.

Don't get me wrong; I would love a 3 rotor as much as anyone else, but it introduces several complexities (multi-piece e-shaft) that increase cost significantly.

I was dreaming about this again...and I needed this thread to bring back to reality...

:tear:

I hope a wider 13B (15B I guess) and direct fuel injection can cure my ills....lol. Trying my best to avoid a future Turbo upgrade...but it seems the chips are stacked against me.

I love NA power, but it seems I will have to give in...in the future.

this same subject came up in my thread on the rx7 forums. im not on these forums alot so none of you know me, but i am a machinist and i DO have the capability of making a 3 rotor renesis intermediate plate if it is possible. i thought i would just like to share with you renesis people what had popped up on the other forums. maybe i can find some help with coming up with a real design for the plate, or a reason why it WONT work, or if its already been done...

when i first saw this thread, the title kinda suggests that 3 rotor 13B's (20B's) are something new, when they really arent. just search the rx7forums for 3 rotor or 20B and you will get tons and tons of info on how to do it. now to my understanding, a TRUE 20B renesis is something new...

i will rob a bank to get a renesis 20b 3 rotor in the next rx8.

if someone can confirm or deny if this theory will work, i will have one designed and made, and ill sell it to you. i just need to know if its going to be a major waste of my time or not.

we need a Fantasy forum ...

You will need a 2-piece e-shaft to assemble the 3-rotor, and of course custom intake and exhaust manifolds, ECU, an extra ignition coil, and 3 additional fuel injectors (if you keep the EFI like the stock setup).

those are things needed for every 3 rotor, no big deal.

the only thing that concerns me for the renesis 3 rotor besides the intermediate plate is the jet air thing, and controlling the 3 additional intake ports through the electronic throttle body.

im truely just looking for someone who knows a GREAT deal about the renesis, and if the sketch of the intermediate plate will work in theory. The intermediate plate is the only true issue at the moment since its the only part that does not exist at all, and has never been made. oil pan, motor mounts, ecu, etc... all of that minor stuff needs to be changed with a conventional 20B anyway, so those are not a concern to me at all. the majority of the design theory is the same except the intermediate plate and the new 3 port per rotor intake.

Retaining the S-DIAS system could be tricky.

you wouldnt. enitirely new intake manifold as you said. no sdais.

Stop playing with my emotions driveslikejehu..... :(

I imagine something like the 20b manifold could be made to work, but otherwise you are fabbing up something. His goal was a 3-rotor Renesis, and IMHO, one of the things that defines the Renesis (besides the all side port config) is the S-DIAS system. SDIAS is responsible for several points in the power curve where the engine can achieve over 100% VE. Obviously not necessary, but it would certainly be beneficial if the 3 rotor is to stay NA. A 20b manifold (which was for an FI application anyway) would probably not be ideal for a 3 rotor NA renesis.

agree totally. gettingthe lengths right is just some fancy math that some on this board can do. the barrels etc could be had from mazda using renesis parts. some aftermarket comps (motec etc) can operate solenoids/ports. so really its possible. just not something i would expect from the aftermarket. but doable- if you're already speccing the intake manifold why not?

Is it me...or is the list of parts needed not very costly in my opinion? I know little about aftermarket stuff but I just don't see the 15K price needed for such a build. If you use most of your current Renesis the cost of maknig it 3-rotor should be minimal.

Honestly, if driveslikeajehu is able to build a kit he could sell to the common joe nutbolt so he/she could build their own 3-rotor that would be great.

I know it's been asked before, but let's come up with a list parts and give a fair price for each part (labor to build and the material needed). Like that we all would have a better idea of what it takes.

Once you build the first custom parts and made molds of them (or used a fabrication computer/machine) it shouldn't be too tough to just keep building the parts needed and sell them like they sell Turbo kits.

If this was possible...I'd go 3-rotor instead of turbo one day.

Most people probably wouldn't go through the trouble. But I agree, its completely possible. But its just another piece of the puzzle. My point was that there is a LOT more to think about when considering building a 20b out of parts.

at our machine shop, we can make ANYTHING. he have CNC Mills, lathes, fully computerized bandsaws and presses, every type of welding you can think of... probably over 20 different machines (some I dont even know what they do), and people who know how to use them. so fabrication and machining... simply isnt an issue.

the only problem we would run into, is that we dont have anyone thats very experienced with the renesis (hence the reason for this post), although we do have some people and resources for very experienced 13B-rew builders, as well as a 20B builder, and my rx7 to tinker with if need be.

today im going to give some detail pictures to the boss (who does almost all of the CAD and g code work) of all kinds of plates for the renesis as well as the conventional 20B center bearing plate, to see if we can come up with a workable intermediate plate for the renesis with the nessesary intakes and side exhaust ports. of course we will need some different plates in hand to measure exactly, but he will at least be able to tell me if we can do it in our shop. IMO, if we can do that, we can solve the intake issue.

most of the cost comes from parts that a normal person cant make themselves (motor mounts, manifolds, modify the subframe, etc) but for a very experienced shop that can do all the fab work on hand, no its not going cost 15k, probably ALOT less than that. it IS going to cost us alot of time though, especially with the design and CAD aspect, but also with things that we dont need to waste our time with (even though we probably COULD machine them here if we had drawings) like the e-shaft, rotors, housings, etc etc. some things are just better to be bought.

as for making kits... if we actually do this and make a fully functional 20B renesis, without modifying the car itself as much as possible, im sure we will sell kits to whoever wants them, but i doubt we will market them. we have different plans for the design once its completed.

SO anyone with ideas or problems that nobody has mentioned before... feel free to share. oh yeah... we will eventally need an 8 to stick this in... so if you see a totalled or junked one let me know, we will fix it up.

drivelikeajehu there are several knowledgeable people here (RotaryGOD, MazdaManiac, etc etc) that could give you alot more information than I can. Heck...there are people here or maybe even vendors that could also help this project out...take some of the work on themselves to help speed things up.

Go here, this 8 might be useful for something before our poor friend ends up putting it in the grave. https://www.rx8club.com/lounge-4/first-last-time-drag-track-83269/

Go here:

http://www.rotaryengineillustrated.com/renesis.php

For some pictures and information that might be helpful.

I really can't help much but I sure would love to see you build a 3-rotor Renesis. Like I said, I'm the 3-rotor Renesis dreamers club president...lol.

As said earlier, if you want this to have a chance to sell, I think making it retain the Drive by Wire and a modified S-DAIS system is important...

As soon as I reinstall photoshop, I will generate a 3-rotor renesis picture from the previous picture + drivelikejehu's sketch. If for no other reason than to give wannahave a new desktop and to stop his endless slobbering. ;)

Hey, while we're daydreaming, maybe we could replace the cast iron parts with aluminum. That way you end up with a 3-rotor renesis that weighs the same (or less?) than a stock renesis. Oh yeah, and market this to the airplane guys, apparently there is growing interest in rotaries there.

lol :rofl:

racing beat makes aluminum plates, but i THINK (dont quote me on this) they are mainly used for racing applications, as aluminum does not hold up to longterm wear as well as steel or cast iron. i dont know where that came from but i swear ive heard or read that somewhere. someone correct me if im wrong.

i definately want to see this photoshop! my sketch is kinda crude i know, it was one of those frantic things so i didnt forget my idea. i get lost in my mind sometimes. thats why all you guys are here to help me out!

ive gotten great responses so far keep em coming! even you guys who think this is a huge waste of time and money and it will never work, i wanna hear what you have to say!

What about a 4 port per rotor renesis, 2 rotor renesis is 3 ports per rotor

2 end plates would be stock, and the 2 middle plates you'd fab up and have 4 circular intake holes in it and 1 exhaust port, since you are machineing so many parts, you might as well create a new 3-rotor-renesis with 12 ports that can rev even higher!, instead of using what mazda have, why not improve on its design, dont know if more port # is better tho
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Its definatly going to be longer tho, thats the biggest disadvantage i see
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One thing about the intake manifold will be the VDI system. This is a big part of the Renesis intake system. You aren't going to be able to do it with 3 rotors. There will have to be no VDI. This valve effectively changes the intake length. This would be extremely difficult to pull off with 3 rotors. VDI has never been applied to a 3 rotor successfully before. With a large amount of work you could make the auxiliary ports work but I just don't see VDI happening.

Why do all the rotors have 4 ports?

Sorry, check out my previous thread end of page 3, its just an idea i thought up, instead of 3 ports per rotor, perhaps 4 would be better? and 2 identical intermediate plates would make things simpler? maybe?
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