jeffe19007

It seems from the reading I have done on the rotary, and again, I have studied the rotary only since the RX-8 came out, that one of the key limitations of the Renesis is the siamesed exhaust ports.

Otherwise, why look at header design at all?

Whenever I see siamesed exhaust ports, and they are all over automotive history, they exist because of compromises due to the engineering/ manufacturing budget. Not because they were they best way to build the engine. And yeah, I know engineering is about compromises.

Historically siamesed ports (and here I mean for two different cumbustion chambers) were often responsible for bad breathing and hot spots in the engine (I think my V8 reading backs this up but I cannot recall where).

Now that the Renesis has proven itself, And I believe it has, maybe the funds are available to correct any compromises that Mazda had to make to get the project out the door.

I guess what I am getting at that I would like to see Mazda build a halo car (maybe even call it an RX-7) to match what Toyota, Honda, and Nissan are doing. Something like that could happen it they build it on the MX-5/RX-8 platform.

Your halo car would need to make large reliable horsepower and these siamesed ports might be a problem with that. Even with FI.

Sorry for the ramble, but no worse than the rest of this thread.

neit_jnf

widen the center plate, make the center exhaust ports independent and add two more "tertiary" ports with sleeve valves. The engine now has 8 intake ports instead of 6; airflow restriction solved.

Now, make the engine all aluminum, use two-stage direct gasoline injection (stratified charge ultra lean economy mode during idle and light load and cruising conditions and homogeneous charge at heavy loads) and the fuel economy will increase a lot.

tuj

It doesn't make that big of a difference in an engine without any overlap. You're right that everyone in the automotive world knowns that siamesing is a compromise, but in this case, I don't think there was much to be gained from making them separate. Check out the header theory thread.

TeamRX8

iTrader: (25)

don't be naive, a bunch of enthusiasts talking header theory smack is no indication of validity

tuj

You're right man, what was I thinking? I had no idea I was so dumb. But its true, in a forum there tends to be lots of misinformation and opinions. Do you really think the siamesed ports are all that bad? My take is that the engineers at Mazda are smarter than both you and me, but if you read some of these threads you might think otherwise. Its too bad there aren't any of the actual engineers who post on here so we could actually have authoritative answers, but all we've got are math books and sarcasm. I guess I'll just keep up with my usual crapflood.

MikeW

Where is the EGR? Honda still uses EGR [catalyzed] on the accord V6, new civic and others.

4 intake ports per rotor will allow for more intake flow, and wider rotors.

Direct injection in piston engines allows for substantially higher compression ratios, where all the extra torque comes from. ie. Audi 3.1 FSI V6 (not VR6) 12.5:1 compression, and 243 ft-lbs.

rotary crazy

the engineers are not smarter they just have all the information and the tools to try things out plus they get paid for that!

Aseras

i'd say it's that they have deep enough pockets and a large enough pool of consumers to absorb the cost of development.

rx8wannahave

So, and you can flame if you would like (lol), where is the rumor at on this "wide" 15B Renesis?

I read a bunch of this but lost track a while back, can someone summarize how much is good rumor and how much is bad rumor?

What's the guess on what DI can do for the Renesis, without going wide (power and fuel economy wise) and what it can do with also going wide?

Again...even if you answer you can flame me, but I just lost track of this thread and don't care to rummage between name calling, I'm smarter than you accusations, and off topic chat.

Note: I'm not calling anyone out, I've taken things off topic enough to be forgiving of such and more...lol.

globi

I heard a rumor that Mazda is getting sick and tired of the torque, hp and mileage discussions and intends to replace the rotary engine in the RX-8 with the piston engine in the Mazdaspeed 6 (which is already developed). It will have a larger intercooler in the front, slightly increased boost, deliver 300 (actual) hp and the engine will be tilted to keep a low center of gravity.

Brice-RX8

You are not going to see a piston engine in a "RX" car.

globi

Oh completly forgot, I also heard that they intend to change the name from RX-8 to MX-8...

Tirminyl

RX8- Reciprocating eXperimental duh

rx8wannahave

OK OK, I'm requesting kinda sorts factual like rumors not off the wall conspiracy theory (lol)

nycgps

iTrader: (1)

I Dont think they will even hire you to "test things out" if u're not smart enough.

Just my 0.02

and I think Mazda engineers knows what they're doing. The Torque is a-bit low for everyone's taste but its still good.

I think they still need some time to try to get full performance out of this Renesis.

So dont underestimate People at Mazda !

rotarygod

There is no word from Mazda on a larger rotary. The rumor as it has now become, started here almost 3 years ago with an old member named Booger. He asked what the possibility of a wider engine would be and how it would work. It was nothing more than pure curiosity on his part and he started a discussion to talk about the pros and cons. That discussion slowly led to people actually believing that Mazda was working on one. That's where it came from. There is no "wide" 15B Renesis. It's turned into an urban legend.

Floyd

Man, have I been lurking this site for that long already? Damn..... :D

rotary crazy

they are really good, what I meant to say is that they are engineers like any other good engenieer. to give you and example mazda has adopted things that some rotary tuners( not at liberty to tell names) have done on their own an back up their development.

rotary crazy

about the 15b or what ever they call it, it just logical, they have done this 2 times or maybe more ( 10a,12a 13b ), thats why the rumor got so many atention.

tuj

Widening the engine is the easiest way for Mazda to increase displacement. Much cheaper than adding a third rotor, much cheaper than rescaling the rotors and housings. Its a very logical idea.

raspyrx7

if they do make a new disp motor it would initially be XXa not XXb. There was a 13A that never made it to production, and the 20B is derived from the 13B so it maintains that rev conotation. If they're using a 20B in GrandAm series why not go production.... mmm Mazdaspeed WB RX8 20B holy rice killah.

zoom44

no the A and B refer to eccentricity geometries. at least thats my understanding

mazda didnt produce the engines in the grand am cars

tuj

Sorry Zoom44, that's not exactly true. The 15a was an engine that had identical trochoidal dimensions to the 10A/12A/13B. The only difference was the 15A housings were 90mm wide versus 80mm for the 13B. The 21A was completely different in dimensions. So the A and B do not refer to the trochoidal geometries AFAIK.

Also, I thought the 20b's in the Grand Am cars started life as Mazda engines, although they have been heavily reworked by their campaigners.

rx8wannahave

THANKS a bunch RG, that was a perfect response! Thanks for taking the time to explain that...

Everything is rumor it seems and Mazda is HIGHLY mum on the subject, just check out their response to a bunch of questions on rotarynews.com

Thanks again RG!

rotarygod

The A and B designations come from how many different designs of this size they have made. The original 10A rotary was the first 1 liter rotary hence the A. The 12A was the first 1.2 liter and it also used the designation A. The 13B is actually the 2nd engine with a 1.3 liter displacement. The first was of course called the 13A. It had skinnier but taller rotors and differed by 2 cc in size from the 13B which is 1308 cc. The 13A could have been called the stroker version of the rotary family. It was only available in one car ever, only for 2 years, and only in Japan. That was the front wheel drive Luce of the mid 70's. Yes a front wheel drive rotary in the 70's! The 15A and 21A engines were the first tried of that size and although they were never produced, they still have the same displacement minus the decimal point and letter designation. The Renesis is the same combustion shape and size as the 13B and is really nothing more than a revised 13B with different exhaust ports. The 20B engine shares the rotor dimensions with the 13B but at 2 liters in size is represented by 20. The B designation for that engine is a mystery though. I have no idea if there was a prototype 20A or not or whether they just used B since the 13B engine it was based off of used it. Sport Compact Car magazine had an article that claimed there was a prototype 20A but I believe they are confusing it with the 21A. I've never seen it mentioned anywhere else. Mazda has also tried 1 rotor variants off of 2 rotor sizes such as the 6A.

Race engine designations have been a little different such as the 13G 3 rotor race engine of the 80's which was the predecessor to the 20B race engine.