Is 911 engine a true boxer?

[smarjoram]

I've just been reading a fascinating, if somewhat brain aching discussion here...

http://www.atlasf1.com/bb/showthread.php?s=&threadid=12457

It talks about a lot of flat engines being 180 degree Vee's and not true boxers. Here's what one person says...

With a 180 degree V-engine, two opposing pistons are connected to the same crank. When one piston moves to the right, the opposing one will do so as well. A boxer on the other hand has a seperate crank for each piston. In this case when one piston move right, the other one move left and vice versa.

I'm pretty sure the 911 is a true boxer but it's an interesting talking point. Apparently people turned to the 180 degree V to get over vibration issues.

It's a great site. There's also a great collection of weird engine designs...

http://www.atlasf1.com/bb/showthread.php?s=&threadid=1793

[Jim Sims]

It's either a boxer engine or a "Lego" engine; each of the rods of a 911 engine has it's own crank pin. See:Exploded Engine Pic...

Jim

[racemor]

Wow, those guys are soooo far over my head! Interesting though. I like the discussion about cranks, you hear a lot of references to flat crank engines these days and that shed some light on the subject.

Atlas F1 looks like a good site too. A lot more info than we ever get on this side of the pond.

Tom

[smarjoram]

I know, it's incredible isn't it? Until today I just thought cranks were a way of getting the pistons to go up and down. Now I've had my eyes opened to big bangs, twingles, double knockers and more. There are some seriously brainy people on that board.

Either that or they're all mad and it's just a place for them to type stuff so as to keep them off the streets.

[Planter91C2]

this reminds me, the other day i was wondering why rotory engines, like in the old rx-7's aren't more popular. theoretically it seems like a great design.

[masraum]

I think it's a combination of things. I think reliability is one of them. It took a lot of design work to get the seals to work and last, and I think they were still just barely adequate. Also, I don't think they are known for lots of torque which is generally required, especially in the US where we do everything big.

I could just totally be talking out of my butt too.

[smarjoram]

Don't forget Mazda won Le Mans with a rotary engine.

I seem to remember that in general they aren't particularly efficient.

[DavidPorter]

Lousy fuel economy, hard to get the exhaust clean, high seal wear is what I've always heard. All addressed to some degree over the years. The last RX7s were supposedly great cars.

[KTL]

The above fellas mentioned the same stuff I recall. Rotor seal longevity has been an issue (something like 60K mi. on the twin turbos), fuel economy in not all that good, not exactly a stump-puller of an engine.

I will say that the design is really cool. I heard one fella say (owned an RX-3) that they are somewhat limitless as far as revs. It'll keep revving higher, but you run out of power so what's the point in letting it continue to rev higher. I guess they're hard to over-rev? I dunno. Also, although the motor is not all that fuel efficient, it is kinda power efficient. Meaning you get a good amount of horsepower out of a small displacement motor. I think the last RX-7 motor got 255 hp out of a estimated 1.9L displacement. Although that is a sequential twin turbo rotary motor. Still, I think the design is really impressive. Too bad it's never been perfected and widely used.

[NYSCAR]

Yah the rotaries died because they're not very efficient. Their combustion chambers at the peak of compression are long and narrow, not very well suited for good combustion (thus most mazda rotaries from mid 70's on have twin plugs). Bad combusion=poor fuel economy and high emissions. As far as reliability goes, they're a different animal than the piston engine. They mazda rotaries will run forever and handle extended high rpm running better than piston engines, BUT are 100x more sensitive to overheating (relatively thin rotor housings warp and break the coolant passage o ring seals) and pinging/detonation (that's what kills the seals, especially the apex seals). Great for racing, durable at high rpms, lots of power, low weight...but in the racing world there are often restrictions placed on the rotaries to make things 'even'. BTW you definitely can overrev and damage a rotary, but they tolerate it much better (side housing scoring and seal damage vs thrown rods puncturing crankcase.) You can grenade them (rotor shattering etc) but it's very hard to do. The 1st gen RX-7's were the best for reliability, the last generation RX-7's were great on paper, but the production engineering sucked on those cars - insufficient cooling systems and premature catalytic converter failure led to many blown engines.

Brad

[KTL]

Ah ha!!

Good info. there Brad. Thanks!!

[masraum]

That post on AtlasF1 is interesting. I could stop working due to good bbs's like this and that. That's also the same forum that had Vic Elford posting a while back.

very cool.

[Jack Olsen]

The 911 is not a true boxer engine in the strict sense of the term. It is a boxer engine in the common-usage sense of the term.

Here's a post from a while back:

On the boxer-versus-180-degree-V point, I'll concede that it is splitting hairs. And I'll also admit to knowing next to nothing about engine design. Most descriptive terms for engines are just that, descriptive, and have accordingly subjective definitions.

I say the Boxster (or the 911) doesn't have a true boxer engine based on other posts I've read on this board, most recently in the following thread:

What Are The Real Advantages Of Boxer (FLAT) Engines?

Specifically, I'll quote Roger Kirkham, who wrote:

GeorgeK seems to back it up with this posting from another thread:

In this thread.

I, for one, still refer to it as a boxer engine. I guess you could say it's a boxer in the 'commonly understood' meaning of the term. But I wouldn't try to convince an engineer of my point.

[arcsine]

It is a little off topic but I found the AtlasF1 fascinating. Thanks to smarjoram for bringing it up.

One thread that was very interesting was BMW running their F1 engine to 19,000 rpm. The folks did some calculations and figured that was over 150 ignitions/cylinder/second with a linear piston speed of over 5000 ft/sec and an ignition advance of between 50-60 degrees.

Yee haw.

http://www.atlasf1.com/bb/showthread.php?threadid=48011

[Superman]

I'm going to continue to refer to these engines as Boxers, but I appreciate the clarification. Interestingly, it seems my license plate is appropriate. In Washington, if you go asking questions at the places that sell plates, you can find a standard plate that has a little something special. In my case I was looking for the number 911. My plate reads "911 LGV." At the time, I was thinking "large Vee." Okay......

[island911]

Originally posted by Planter91C2
. . . .wondering why rotory engines, like in the old rx-7's aren't more popular. theoretically it seems like a great design.

I had two prof's in school who had done research on using rotary for airplanes. (they're so damn light)
One guy did this for Boeing, the other somewhere in Europe. (think 1940-50 ish)
They both came to the same conclusion. While the reliability issues can likely be worked out, the inherent way a Wankle engine captures the power "stroke" cannot. Essentially, any IC engine need to capture an explosion.
Explosions want to expand spherically.
The geometry of the piston engine approximates a sphere. (under/over sqr, are tweeks)
The geometry of the Wankle approximates a wedge.

What you gain in HP/engine mass, you quickly loose in with all the extra fuel needed.

[JEB]

I drive a first generation RX7 for a summer back when I was in highschool - must have been about 1980. It was a fun car. It would rev forever, and had good low end torque. The suspension was well balanced and it handled very well.

I had alot of fun in that car.

Boy as I read that I realize that was a long time ago. Sometimes I think I may be getting old

Jeb
'79 930
Old man

[724doorE]

So there is no engine that is a "true" boxer????

[RickC]

Does this mean that a 911 powerplant is properly called only a "Flat 6" and that a real boxer engine is just a theoretical exercise - like Plato's mathmatical perfection? Something that never did exist physically - like Justice, etc.?

And, if so - if the term "boxer" is so narrow, isn't it kind of useless? Doesn't it make more sense to use it to describe any flat engine in the same way that "kleenex" and "Windsurfer" and "Jet Ski" paint a pretty clear picture in spite of the actual trade/brand names?

[Harold_89_911]

If I remember correctly, the old BMW motorcycles were true boxer engines. Was that also just a marketing claim? Maybe sombody will correct me on this.