at 9k rpms, the rotors themselves are spinning at 3k rpms. compared to a piston, at 9k rpms, you will have less vibration on the engine

 

I can't believe no one has touched on the real forces at issue here.

The answer to the question of whether the RX-8 rotary is a smooth ENGINE is YES. It is smoother than ANY piston/crank that exists. The closest engine I have experienced is the Subaru opposed 4.

I will now take you beyond opinion statements to scientific evidence...

Piston/crank engines (from here on called PC engines) have reciprocating mass; pistons that move in one direction stop and then move in the exact oposite direction. Imagine a single, vertical, piston for a moment. As the Piston accelerates down, momentum is created and is transfered through the engine. The piston slowly returns to TDC (2x) then is accelerated again. Each time the ignition fires you will feel a jolt through the entire system as moment is created and lost (through friction).

The easiest way to combat this system is to place a second piston attached to the same crank in exactly the oposite direction (horizontally opposed or vertically opposed). Time each piston to fire at exactly the same time and the forces created by the sudden acceleration and deceleration of each piston will be perfectly countered and cancel eachother out (in a perfect controlled environment). The Subaru engine uses this setup to achieve a smooth engine, as well as lower the center of gravity for better handling.

In a "V" configuration (V6, V8 etc...) it is impossible to eliminate vibration due to the direction the forces travel. Most engines of this configuration contain "counterbalancers" attached the crank to try and cancel the forces somewhat. Ask a Harley Davidson owner how well they work though. This also robs the motor of power by increasing the weight and Moment of Inertia of the crankshaft.

Inline 4s do a pretty good job at smoothness due to their even firing order (Piston movement is always well spaced to naturally cancel other piston's force created by acceleration). However, the forces of the downward piston are greater than the upward piston due to the direct force applied to the downward piston (combustion) which will create some vibe.

In any of these situations, if one piston is slightly heavier (even imperceptibly) due to the fact that perfection in milling cannot be attained, that will create a force imbalance and vibration.

In addition to the pistons causing vibe, the valvetrain is fully of parts banging around, up and down, back and forth, with chains that rub (tensioners) and all of that will add to vibration.

Rotary engines DO NOT HAVE reciprocating parts or valve trains.
This is precicely what makes the 8 special. Combustion also occurs much more fluidly as the time between combustion events of 1 rotar is 1/6 that of a single piston (in terms of crank rotation). A 2 rotar engine is like having a V12!!! (in terms of power deliver timing). All of this without a valve train or a single opposed force.

You don't even have to drive an RX-8 to KNOW that it has a smoother ENGINE than ANY piston/crank driven automobile (this is not a matter of opinion or seat of the pants "feel").

This is not to say that the ride is smoother or the engine is quiet. All this means is that there are virtually no vibrations sent from the engine into the chassis.

 

Thanks Doc.. You got a good old fashion belly laugh out of me and the wife for that one!

 

Your RX8 has a radio? Hmmmm, lemme go check this out...

 

It's true. The drivetrain seems to be totally isolated from the car. If there is engine vibration, it does not get through to the steering wheel, the pedals, chassis. The only perceptible vibration can be felt through the shifter ****, but it is part of the powertrain.

 

sit at 80mph in 6th and depress the accelerator fully - on a decent flat road. You start at 4000rpm.

The car just glides. Not quickly(as your in 6th) but it just goes faster with no vibration or hastle. THATS what shows its smothe.

Its also a sports car and performance engine so will sound loud and noisy - it has to brethe. Dont mistake sound for smotheness.

 

attesting to the smoothness of the engine, i was driving home from south beach last weekend up highway 75. I had the car in 6th gear and was just constantly accelerating but not looking down at the speedo. When flew up on a car that seemed like it was not moving at all i looked at the speedo and i was doing 123. I could not believe. Except for the idle, which i still have yet to get the "M" flash just becuase I am to lazy which would probably fix the problem, this engine is smoother at high RPM's than any other car that I have ever driven

 

I don't usually have the radio on, but I once had it up loud and didn't know I was close to redlining it in 3rd gear. The car does make noise, but if you eliminate that, you really can't tell if it's high or low in rpms.

If that isn't smooth, I don't know what is.

 

Can't comment on many of the cars questioned, but I just traded in a 2003 VW Jetta with the 1.8T. Jetta was a great car. RX-8 is superior in so many areas, I don't know where to begin. Mostly, the "fun" factor is much greater with the RX-8. I'm finding fuel consumption, performance, etc. to be neck-and-neck.
IMHO>Tony

 

Good God people do some learning, and searching, and reading about engine designs and their inherent balance and/or lack there of. To start with, a rotary is fundamentally balanced and an inline four is not. Period. No matter how hard Honda or anybody else tries, an inline four is going to be a harsher feeling and sounding engine than a rotary. Or, an inline six or V12...

The smoothest engines have perfect primary balance: sixes, inline and flat, and their variants: vee and flat twelves. Inline fours are fundamentally unbalanced - it takes a balance shaft, or two, to smooth them out. V6's? Unbalanced. You have to offset the crankshaft angles to get something approaching smoothness. The only inline fours I've driven that felt reasonably smooth are the counter balanced ones, like the Porsche 944. V8's can be designed to be relatively smooth, but they are not fundamentally balanced. They usually have a harmonic balancer or other device added on to smooth them out.

Do some research and learn about how firing order and crank throws affect smoothness and "balance". It's great reading, and you'll understand more about engine design.

The rotary is extremely smooth as its two rotors balance each other out pretty well. I'd put in it the same league as a well designed and built inline six. Yes, I'm extremely biased towards inline sixes because they're simple and elegant, and you can design them with a really even power band. And, they sound fantastic. The only criticisms of inline sixes and V12's is that they require a pretty beefy crankshaft since the shaft is relatively long, and the length of an inline six (and V12 for that matter) engine means the car will have a somewhat long hood. Hey, is there anyone who doesn't like a car with a long hood? Many of the world's classic cars have long hoods.

My only subjective criticism of the rotary: its song isn't very interesting because there's not much complexity in its tone. After all, there're only two rotors and an eccentric shaft moving around. Still, it sound's pretty cool. But, in an inline six, you've got a bunch of stuff moving around, six cylinders worth of pistons, rods, and valve gear, and it goes around in a really pleasing way. It's been characterized as sounding like "ripping canvas".

Don't get me wrong; I really like the rotor motor. I just like an inline six more. But, RX-8's don't come with inline sixes. In fact, only BWW and Lexus offer them in cars I would be interested in, and I didn't want to spend for those cars and my '94 325is was getting a little long in the tooth. The RX-8 is unlike any car that BMW and Lexus make. I think the rotary sounds best constantly winding up through the gears. At steady state throttle, I'll take a multivalve inline six over everything else except a V12... V8's? Had 'em, love 'em, but sixes and twelves sound more complex and sophisticated. The rotary is somewhere in between.

Road and Track had a great article within the last few years about what exactly makes an engine sound good. It has to do, interestingly, with the same principles that apply to music; fundamental frequencies mixed with certain kinds of overtones (harmonics), sound pleasing to the ear. Inline sixes and V12's produce better sounding overtones, in addition to their fundamental sounds.....

 

Great post, LOL. I totally agree, the 8 is a one person car to enjoy, or you must have the right passengers. My 16 yo and 5 yo love to drive with me. My better
half and my 8yo complain. I think it depends on if you like rollar coasters or not. i.e., enjoys g-forces or get sick under abnormal Gs.

 

If you want to compare hp vs smoothness, I have never driven a car that is more smooth. If you want pure smooth, drive a sohc 100hp car like my 95 golf, and you get really smooth, even more so then my rx8, but just no power. Once I get my car going past 4k rpms, I do feel the hp kick in, so in my point ot view it's not a pure straight up dead even power curve, but it is certainly quite a smooth running engine. It's also deceiving, because the car doesn't feel as fast as it is. With the smoothness of the renesis, comes lack of power compared to cars like the g35, 350z, and of course turbo charged cars. The mazdaspeed rx8, if it comes out in US will certainly lose the feeling, and will give you a hard kick, unlike it does now. Personally though, for daily driving, the rx8 as it is is a fun car to drive, and great for all around performance and daily driving. I'm still getting used to it myself, but I wouldn't mind a s/c in this car, so you can still get the same feel at lower rpms until you want car to take off and pull you back in your seat.

 

LOL!!!:D :D :D

I know the feeling

 

Here's a vid of my wife taking off, shifting at 7500RPM...

Get an idea of how it sounds from the outside.

I love it.

The car is bone-stock, btw.


http://home.comcast.net/~noel16valver/MOV00277.MPG

 

HMM... Is it just me or it seems like this "RenesisPower" character is just toying with the very basic Idea of a R-Engine? Of course it's smooth! It's a rotary for god-sake. Maybe you don't even own one at all "R.P"

 

BasenjiGuy, since you do so much reading you must know that the vibration perceived by the car's occupant may start with the engine characteristics but has much to do with the way the motor is mounted and the structural stiffness of the body.
There is eccentricity in the rotor movement, and while the pairing of the rotors may cancel the lateral forces, I think a slight sideways rotational wiggle (about the vertical axis) gets through. You can feel this in the shifter at some engine speeds and loads.
The very light motor and very stiff body structure may have as much to do with the perceived smoothness of the car as the inherent balance/imbalance characteristics of the Wankel.

 

I routinely forget that I'm running in 4th gear at 65-75 MPH if that gives you any indication. Every other manual vehicle I've ever had was BEGGING to be shifted well before that point. It has a rev linearity like a street bike and as someone put it, it's smooth as a baby's a$$. I drove the G35 sedan, the 350Z, the S2000, and my wife has an Accord V6 (240 hp). The G35 sedan and the Accord are smoother, but they should be....they're family sedans. The S2000 was too buzzy and it felt like I had to run it to redline to get any power out of it. Despite it being faster according to the car mags, it doesn't feel faster to me. The 350 did feel faster because of the torque, but the suspension made me bleed from my kidneys after a short drive. You'll feel every bump in the Z, but it has impressive acceleration. I got a little off subject, but that's my $.02.

 

Osisris,

As said before I have owned an RX-8 since last August. I guess the issue of smoothness is relative to what you are used to. Most of my previous cars have been big German V8s so compared to the 8 they are much smoother at any RPM.

This is my first rotary and in particular 1st gear over 6K RPM does not seem smooth to me, it is rather loud albeit vibration free.

 

I think we need to define smoothness. Because noise does not equal smoothness.

Naturally the car is louder, you're doing WOT and reving it up to 9k rpm!

It's still smooth even at redline.

 

EXACTLY! Thank you! 'Nuff said...