Before anyone gets offended -- I neither own a 350 nor an rx8, nor am i here to do an rx8 vs 350 comparo. I think both are fabulous cars, with each having its pros and cons.

My question is about its rotary engine. When browsing many of threads, something that comes up as being unique and a bonus of the rx8 is the fact that its powered by rotary engine.

What exactly, besides the fact that is very unique, makes the rotary engine that much better than a traditional engine, or say, even a iVTEC engine (such as that found in the s2000).
From what I can gather:

Engine performance characteristics are similar to the s2000 engine:
- moderate, flat torque
- peaky high hp output
However, beyond that, it goes downhill from what I can gather:
- produces alot of heat
- poor mileage
- oil burning issues?
- and simply the fact htat it is unique, and that probably difficult to work on for ppl unfamiliar or when it comes to parts, etc.

What are some of the other pro factors that I am missing in regards to the rotary, that make it so desirable to have in a car?

Note: Probably due to my lacking knowledge of the rotary, i find it less appealing to get the rx8 because of its unique engine. aside from that, I think its a great car!

thanks!

 

Well for one thing, It's quiet and smooth. No piston engine can reproduce the feel of a rotary. It's quite unique and intoxicating.

 

In a word... weight.

Excess heat I don't think is an issue of the engine though I can be corrected on this. Mileage it's true, there's better results to be desired. Its willingness to rev, only three moving parts, compact size and reduced weight make it a more ideal engine for a sports car.

For example... if you had the RX-8 with a rotary engine the SIZE (I'm talking physical dimensions) of the 350Z engine... you're looking at a 3 rotor engine, and you're also looking at about 400+ horsepower (and that's be conservative). Sure, the torque may run down to 200, 250... but with 400 horsepower the 350Z will be toast. This is of course assuming, that they can use their porting methods on a 3 rotor design.

So in the end, the real advantage of the rotary is weight and size. It allows the engine of the car to be mounted near the middle, and keeps the weight of the car down in the front so that a 50/50 balance is easier to achieve.

There aren't any oil burning issues on the RENESIS, just a sensitive oil LIGHT Being that it's unique might be a downside but with only three moving parts... there's little to go wrong with the engine. It's generally something else, specially since this is naturally aspirated.

 

Now, I can't express the facts about the renesis enigne, cuz i don't own one, but I can tell you about the feel of a rotary. Once you go rotary you won't go back. I've gone from an RX-5 13B to a RX-7 T2 ... and I can tell you! When you rev up a rotary you'll be craving for more rpm:s ... the more rpm the better the engine will run. There's no substitute for a Rotary @ 6500-7000rpm.

Acording to my service manual my RX-7 needs service every 5000km (dunno what that is in miles). From 0 - 5000km the oil meter will go from full to low. So if you pay close attention to your services and don't forget em you will not even know about the oil burning issues.

Mileage is always a question about how heavy your right foot is. 2,5l / 100 km is not that uncommon in my case :D , i have quite a heavy right foot!

The fact that's it unique is often mistaken. The rotary, even though it has a triangular shape piston, the rest of the engine is the same as any normail combustion engine.

Acctually, why do you care about what heat it produces? Mazda has figured all that out for you. But you're correct by saying that is produces more heat! What i've read, a normal enigne has an exhaust temp. around 800-900C degrees. But the rotary has about 1100 degrees C. But why place that as a con... !?

sorry about my spelling. I'm from Finland and I've had quite a few beers when typing this :D

 

I'd say your forgiven, given the circumstances

The RENESIS is my first rotary, however I have been following this unique engine for 25 years. I'll grant you, Honda has tweaked the little 4-banger in the S2000 very well, and has proven itself reliable. However as mentioned by some of our other posters, the smaller size & weight of the RENESIS allow its placement low and back, giving the host car (in this case the RX-8) superior handling characteristics.

That is the biggest advantage. The next biggest is the sound while it revs -- nothing else quite like it. Next is the smoothness while it revs.

 

I would emphazise on: a lot less moving parts: 2 Rotors + Eccentric Shaft.

A 4 stroke piston engine has, well....quiet a few more moving parts: 4 Pistons (for a 4 banger), Intake & Exhaust: valves, arms and springs, Connecting Rod, Rod Bearing, Crankshaft. (Anyone with some more engine knowledge might be able to add to my list.)

Again, I would suggest to put the number of parts involved at the top of the list of pros.

 

A reciprocating engine.... well it RECIPROCATES! Much more vibration than a rotary. Plus, power is only produced on one of the four stroke cycles (per cylinder).

The rotary engine's rotors are moving in the same direction as the output shaft, as compared to the violent reciprocating motion of the pistons being transfered to the rotation of the crankshaft.

Hmmmm.... a rotating force being transferred to an output shaft which is rotating in the same rotational direction.... or up and down motion transferred to a rotating (crank)shaft. Wonder what would happen to that crankshaft at 9000 rpms?

A lot less (moving) parts also is a plus in my book.

And if we ever run out of dino based petrol... we can convert these rotaries to burn alternative fuels a lot easier than reciprocating motor can. Maybe my great-great-great-great grandson/daughter will like a hydrogen based 8.

Peace.

 

According to Mazda the rotary engine has 47 moving parts. Counting all seals... and a ordinary engine has about 247 moving parts!

 

Valve guides, VALVE STEM SEALS, cam shafts (dual usually), cam shaft housings, TIMING BELT, T.B. tensioner, T.B. dampeners, T.B. pulleys, valve springs (spring "float" = point of max. rpm - usually), rocker arm assemblies, valve tappets, push rods anyone?, piston rings...

I lost count how many head jobs I've done, mainly due to leaky valve stem seals. Of course, while you got it torn-down , you might as well decarb every thing & re-seat the valves. Lottsa fun!
I nearly lost my Fiat engine onc due to a broken timing belt. Afte fixing it, I became a faithful timing belt maint. sched. follower.

I rebuilt my 1970 Porsche 911E engine a while back. Impressive design to be sure. Horrizontally opposed 6 w/ mechanical fuel injection. Anyway, by the time I had it all torn down, all those parts laid out nice and pretty for a photo shoot took every bit of my 1-car garage! Just nothing but engine parts took up the whole garage!

About weight & size, the Renesis reduces the weight, CG height & polar moment of inertia. If this was a game of five card draw, you can bet that I would hold those three cards. You can play with trick suspensions, real nice brakes, tires & wheels, racing seats & steering wheels & stuff. But if you're gonna start with a regular car & trick it up, you still have a heavy, big engine which adds to the GVW, CG & Ip. A bad hand.

 

A lot of the key points have been touched on of why the engine's unique - smooth operation, revs great, less moving and complicated parts, etc.

One thing the piston engine has an advantage on the rotary is the decades more research and development behind the piston engine. Mazda is the only company working with the rotary in a mass-produced auto right now - as good as their engineers are, there's something to be said for competitive engineering.

That said, another key point is the amount of power you can produce from such a light, small, and simple package. The amount of power a rotary can produce is more akin to a 6-cylinder engine than a 4. I think the record output for a two-rotor engine would be Scoot Sport's 730-some horsepower engine - wow!

The three rotor is a whole 'nuther beast. Hercules, your statement about torque and the three rotor is a bit off - every one I've know who's driven a 3-rotor powered 3rd gen RX-7 was SHOCKED at the amount of torque the engine produces. 60 MPH in 5th gear? Just stomp your foot to the floor if you want to light up the rear tires. I would love to see Mazda pursue the 3 rotor engine some more - only time will tell there.

What it boils down to is the rotary is the perfect engine for a sports car - very small and compact, very lightweight, and very simple.

You guys ought to tear down/rebuild an engine sometime - it's really something. I've built probably around 15 motors, and it's just SO darn simple inside. Taking my time, an engine build takes around 1-2 hours. No kidding. There's a lot less precision work and machine work involved as well - fit seal A into slot B, stack together like a big sandwich, voila!

Dale

 

Rebuilding an engine easy? I'm so mechanically deficient that I have trouble building a peanut butter and jelly sandwich.

Anyway, to me the best part of a rotary is it's smooth, linear power delivery. And the more you push it, the more it wants.

 

FYI: For a Rotary engine, it is normal to burning a little bit of oil during regular operation. (But yes, a very bad thing for a piston engine)

 

Um... yes...and, no.
"Easy" is a relative term.

You must still have a mastery of the tactile "intuitive" torque wrench in your hands which comes only from "accidently" over-tightening a few. That's called "experience", "hard knocks" & "learning something the hard way". He he. Still, there are some critical bolts which even (especially?) the hard-core pro's resort to a torque wrench to tighten to the exact torque. So, ya gotta own one, or know someone who will let you borrow one.

Lots of other stuff you just gotta know, too many & too hard to come up with to list them all. Gaskets, what sealant to use on them - if any. Threadlocker? What to use to clean various kinds of parts. Cleanliness is real important.

When you tear it down, then what? Just put it back together? Don't you want to check things to see if it's worn or not? How do you do that? By knowing what the things should measure (spec's from a good manual) & then measuring them acurately, with micrometers & other kinds of measuring equipment & tools. This is what is called "blueprinting" an engine. Lots-o-fun!

Other tools & supplies will be required which you probably don't have yet. Also, a real good manual is an absolute must!!! Never touch an engine without knowing what you're doing! To do so is just plain (duh) stupid, so get a very very good shop manual, with lots of pictures and step-by-step detailed instructions!!!

Ah. If you're young and a man, get to talking with people who know this stuff & they'll show you lots of things & even help you - usually the help is minimal, just enough to get you out of the woods. That's just how it is.

I know one thing - I saved many thousands of dollars doing it myself for over thirty years now. Still got all my fingers & toes too! Sure do! Got a BS in mechanical engineering too. Not from working on engines though. But it helps when I work on an engine, that I know what I'm looking at - usually. This rotary is cool. Would like to see it's innards. Not out of my car though!!! No time too soon anyway!!!

Find an engine & rebuild it. Just give yourself plenty of time. It took me over 6 months to do a 911 engine. See, I didn't care how long it took, I just wanted to get it right. The people I worked with were more upset about that than I was, for crying out loud. In the end, I got it right (new Mahle matched pistons & jugs, cc'd the heads in my kitchen, farmed out the throttle linkage assemblies & butterfly valves to a place in California, stuff like that...) & that engine was something I'm still proud of.:D

 

Really, building a rotary IS easy. All the crap that bolts on to it is a whole 'nuther story...

The rotary is truly an air pump at its simplest form. The seals on the rotors are just floating seals (with springs behind them) to form a tight fit against the stationary surfaces. There's far less precision work required than a piston engine, especially since there's no pesky head .

It's this easy -

- Clean all the parts you're using and make sure they're not visibly damaged - gouges in a rotor housing, etc.

- Put the oil seals and springs, apex seals, side seals and springs, and corner seals and springs into each rotor.

- Take the front iron housing, install the water seals into the grooves, then set the front rotor onto the stationary gear.

- Place a rotor housing on around the rotor, and install the dowel pins and dowel pin O-rings on the rotor housing.

- Stick the eccentric shaft in

- Install apex seal springs.

- Put the water seals on the center iron, lift eccentric shaft a bit for clearance, and add that to the stack.

- Place rear rotor on the stack.

- Install rear rotor housing with dowel pins and seals.

- Install apex seal springs.

- Install water seals on rear iron housing, stack that on.

- Install the 18 tension bolts, tighten in order to 25 foot pounds.

That's it - that's the equivalent of installing main bearing caps, rocker arms, cams, camshafts, EVERYTHING on a piston engine. You could do the above in probably an hour if you were taking your time.

Since the rotary breaks into smaller pieces than a piston engine, if the housings are scored or damaged, just pitch it and get a replacement. Replacements are plentiful and inexpensive - I just bought a good used rotor for a motor I built for $30 shipped.

But, as I said at the beginning, all the crap that bolts on to the engine is where people have trouble - that DOES get complicated. A lot of it is simple stuff that inexperience mechanics get lost on - vacuum leaks, electrical connections, use of gaskets, etc.

But, at least the engine is easy!

Dale

 

Almost forgot to mention -

http://www.rotaryaviation.com/overhaul_video.htm

Bruce Turrentine is a VERY skilled engine builder, and he walks you through the whole process. The video is excellent, and all the facts are right on the money - Bruce also shows a bunch of little extras he likes to do when building motors.

Highly recommended!

Dale

 

I've wanted to take a shot at doing some mechanical work for years, but since I live in a high rise, and have my car in the garage - where even washing the car is forbidden - at the moment I'm out of luck.

Just something I'll have to try and do down the road.

 

Well it looks like theres a lot of great info here for you.

While you said the reason that you wouldnt get it is because you dont know much about it and its uniqueness, I would have to say that, that is I always thought is one of the reasons many people are attracted to it.

There is an aura about it.....


Theres a lot of nostalgia surrounding the wankel, and while thats good I really think mazda is pushing their car more into the mainstream.
Its a fabulous engine. Its going to be interesting if reliability issues ect come up 5 to 10 years down the road, I wouldnt be surprised if you see these engines getting close to honda territory as far as engine life.
Mazdas put a lot of research and it should pay off.

 

Eh~ I don't know about that. Hercules told me the Renesis only has three moving parts?

The benefits of Renesis engine:

1) Lighter
2) Higher rev (even though piston engines can do the same)
3) Smaller and achieve lower center of gravity
4) Unique and special
5) Damn it's smooth. :D

Negatives: I'll let other people cover this one.

As far as 3 rotary goes, it produces amazing power/volume ratio in a small package. I suppose people can always say a 3L rotary will be more powerful than a 3L piston. However, unless we start seeing 3 rotor engines in CURRENT production cars, it's a null point. I want to see a reliable Force Induction Renesis, because that's the way a performance rotary engine is meant to be.

 

It does only have 3 moving parts.....the eccentric shaft, front and rear rotor, those other 44 parts are located on the rotors and shaft but their not moving, but they are on the parts that do move.......the seals, apex, corner, sides, oil seals and springs, their job is to seal, not let air escape which leads to lost compression, ect.

I probably got you all confused now.

maybe we can have a rotary 101 class at the local community college...lol

 

Kinda funny too is that honda is dropping the redline on the new s2k because of engine problems that had to be covered by warrnenty which were attributed to the high revving engine. (Supposedly hopefully a s2k guy can confirm this for me, or explain ive been wondering why for a while now).

I for one wish they would keep the redline and throw in a 2.4 k24 or so in there. But i guess hondas wussing out oh well.

 

Thanks guys very informative thread.

 

Theres a lot of books out there on the rotary engine some of which might be out of print, you can always find people selling them on ebay, sometimes your local library just throws them out.

Its an interesting story though.....remember the conventional piston engine had a big head start on the rotary, at least 75 years before many of the bugs were worked out, were just about catching up..........

 

...anyways...

lookee here:
https://www.rx8club.com/rx-8-faq-9/engine-tech-info-8968/

(i don't sticky things for nothing )