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  #1  
Old 06-03-2001, 06:54 AM
David C Klasse's Avatar
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I was in a friend's Boxster, and relearned that it was a flat 6.

I have a very general idea about the pros and cons of each are, but would anyone mind elaborating?
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  #2  
Old 06-03-2001, 08:56 AM
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A Boxster is a rockin' car! A flat 6 engine is also called a boxer engine because of the way the pistons resemble the way a boxer jabs.

A F6 is supposed to wear less than an I6 or V6 because of its configuration. It also has a naturally lower center of gravity. I don't know of any other pros or cons.

Kuan
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  #3  
Old 06-03-2001, 08:56 AM
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it is my opinion that

the flat (or "boxer") engine arrangement probably leads itself to be the "smoothest" running arrangement.
Jim
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  #4  
Old 06-03-2001, 09:11 AM
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"Boxer"

As I understand it, the term Boxer came from the pistons' appearing to be 'boxing' each other...what do you think Kuan?

Of these arrangements, a straight six is the smoothest. However, it's the least easy to package (which is why they're often canted over to one side) and potentially has the highest center of gravity.

A flat six works better than the other configurations for Porsche for a couple of reasons:
1.) Low Center of Gravity
2.) Air cooled

A V-6 is a great configuration for packaging, but is only smooth when including some sort of active balancer to get rid of huge 2nd order vibrations (whatever the heck they are-engineers please chime in here); virtually all modern V-6s incorporate a crank-driven balance shaft of some sort

As to Kuan's contention that a flat 6 would wear less than the others, I'd not heard that nor do I really understand why that would be the case. Anyone care to elaborate?

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  #5  
Old 06-03-2001, 10:01 AM
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The longevity of the engine really depends on the who made the car. I used to have a VW parts hauler which had the engine rebuilt at least 2.724 times! The supposed ideal angle is (2*360)/number of cylinders. So for a V6 it would be 120 degrees. I don't know why the boxer would be so smooth but it is. Maybe it's one of those bumblebee things where we know that it should not be able to fly but does!

I too have heard the pistons boxing each other explanation for why it's called the boxer. I've always had a hard time visualizing this. Somehow my VW experiences have tarnished this image! The other advantage to the flat 6 is that you could drop it out of the body with nothing but a floorjack and two jackstands. This is a 20 minute job if you've practiced it a few times

Another advantage (on a VW, never tried it on a Porsche) is you could if forced to, install one just one new barrel and piston if you needed to. I guess it's possible in principle on a Porsche aircooled engine, but chances are slim that one would have an extra cylinder barrel and piston in the car!

Kuan
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  #6  
Old 06-03-2001, 12:03 PM
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Ok, "boxer" comes from the H4 (horizontally opposed 4 cylinder) design. With two pistons on either side, it looks like the left right punches from a boxer from each end. A boxer is supposed to be the smoothest running due to the natural balance of 180 degree matched motion. This requires the least additional balance load on the crank shaft as well.
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  #7  
Old 06-03-2001, 06:39 PM
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there are 3 engine configurations that are inherently perfectly balanced:
* inline-6
* flat-6
* 60-degree V12

the typical American 90-degree V8 can be brought into perfect balance via the use of counterbalance weights.

A Ferrari V8 however is different. Although it is also a 90-degree V8, it has a flat crankshaft (i.e. the throws are all on one plane). Although not perfectly balanced, it has an even firing order (i.e. the engine pulses are regularly spaced), which gives it better high-rpm breathing and that distinctive shriek that cannot be mistaken for the typical American V8.

V6 engines are not perfectly balanced. I believe the 60-degree V6 is easier to balance than the 90-degree one. (benz went for the 90-degree config to leverage the same assembly line components of its V8 engines).

I view the term "boxer" differently: if you were to mimic with your forearms, the way the connecting rods of the opposing cylinders move, you look like a boxer using you arms as a shield.

A flat-6 has the lowest center of gravity and perfect balance. But its exhaust plumbing is very convoluted considering the small spaces available. And since it sits down low, it is more difficult to service.

An inline-6 has perfect balance but is the longest, which makes it more difficult to package. A long crankshaft is also inherently less stiff than a shorter one (like those on H6 and V6 configs), other things being equal. But intake and exhaust plumbing are simplified because they are on opposite sides of the engine. This makes turbocharging simpler than with a V6 or H6. You can also place heat-sensitive components on the cold (intake) side of the engine.

A V-6 does not have perfect balance but is very compact, and can be mounted transversely or longitudinally (the extreme example is the VW VR6). If mounted transversely, exhaust plumbing is a challenge. The space in between the banks simplifies the intake plumbing, and makes it a natural for superchargers, especially for a 90-degree V6, which has a bigger space in that Vee.

They also make different sounds, because of the differences in exhaust pulse patterns.

An inline-6 has a simpler valvetrain, because there is only one head.

Finally, an inline-6 looks the sexiest from the engine bay, what with that long *thing* in there, and with those exhaust headers in plain view ... it's a guy thing ... ;-)
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  #8  
Old 06-04-2001, 12:55 AM
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re V vs inline etc

Also in reply to the above examples the v6 layout I am told has more torque than an inline 6 but the inline 6 is inherintly more smooth running and is generally more balanced as was mentioned before.
The v6 therefore all things being equal should be a better motor for pulling and hard work (Tradesmens reqirements) thats why there is a lot of jap pick ups around.
we see this a lot down in Australia.
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  #9  
Old 06-04-2001, 01:13 AM
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Yes, I think that an inline 6 sounds more refined. I drove the CLK 320 today and it sounds more gruntled, like meatier, or more of a low tone. The C280 and the CLK320 seem to be about the same speed, acceleration-wise. But the inline definitly seems smoother and more refined.
My mom's Porsche has a flat six. I never really thought about it though. How are they able to get more power out of a 3.6 liter flat? That engine is just loud!
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Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
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03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
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  #10  
Old 06-04-2001, 01:37 AM
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All to do with airflow

Im not a mechanic but im just interested (Im a Chef by trade)the difference is the rate of airflow dynamics and sequence of revolutions I think. with the v and flat motors the makers are able to get much more airflow and direct ramming(Turbo & Supercharging)without splitting the airflow which creates horsepower, but you sacrifice smoothness(Inline) the motor is actually a large air pump the more air that is fed through the motor the more power is created.
Thats why the japs run small motors in WRX"s and EVO"s but produce high HP And KW The Subaru is only 2litre but has phenominal power for small car (It has boxster layout like the Porsche also) but is turbo charged .
The newer benzes are comming out with V6 motors with supercharging and they are reasonably economical and have great torque so im told.
Maybe there is some tech out there able to verify these pionts im not totaly certain if this is correct (Im only a Chef not a mechanic as i said, just interested)
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  #11  
Old 06-04-2001, 02:39 AM
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among other things, the V6 differs from the inline-6 in terms of the timing of the exhaust pulses. The inline-6 has evenly-spaced cylinder firing: a cylinder fires every 120 degrees of crank rotation (it's a 4-stroke, so you need 2 revs for a complete cycle). This gives it a very uniform torque profile at the crank, measured against crank revolution.

in a V6 however, the cylinders do not fire evenly with respect to crank rotation. Pairs of cylinders will fire closely together, which gives it that rougher exhaust note. Since a pair of cylinders will overlap more on their power stroke, the maximum torque reading on the torque profile could be higher than that of an inline-6.

However, the flywheel dampens out these torque fluctuations, so we do not notice them at normal rpms. On cars without traction control however, you might notice the difference between the 2 engine configs when you do a tire-spinning start: because the V config has a more ragged torque profile (and higher torque peaks), i believe it will produce a more irregular tire spin than the inline-6. It will be noticable because at low rpms, the flywheel cannot smoothen out the torque fluctuations enough.

I've seen a slo-mo video of a Porsche 968 (with the biggest inline-4, it produces a ragged torque profile) on a tire-screeching standing start, and you could see the rear tires spinning and stopping repeatedly, each spin corresponding to one of those big cylinders firing.

an American V8 produces a "burbling" sound at idle because it has 4 pairs of exhaust pulses, each cylinder firing closely with its pair. The Ferrari V8 produces a different sound, because of its even firing order.

the best example of the effect of a V config on engine sound is a Harley-Davidson. Not my cup of tea though. For me, the best sound is a small-bore Ferrari V12 at full scream ...

also, the exhaust plumbing also affects engine output. You want to optimize "scavenging", and you would want to consider the firing order in designing the way the pipes merge.

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  #12  
Old 06-04-2001, 12:56 PM
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Something else to note about a "flat" configuration as opposed to the other types:

The engine "case" as opposed to a "block" supports the opposing dynamics of the pistons, contrary to an engine block, which requires huge "mains" to keep the whole setup from pushing itself out the bottom.

By the way, Subaru also uses the flat configuration on their 4-cylinder vehicles...

I found this to be an interesting topic, given that all of my vehicles each have a different engine configuration...
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  #13  
Old 06-04-2001, 01:14 PM
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These flat fours are favorites of Home-Built
aircraft.
They are light and the VW is air cooled.
Good prop torque at low rpm. No need for gear
reduction.
I had a converted 1600 cc one with magneto and steel crank and used it to power a VolkPlane VP-1.

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  #14  
Old 06-04-2001, 02:29 PM
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Others

What about the BMW (motorcycle) boxer, and the old Corvair flat air cooled six?

One thing about the V6 is the crank has to have split journals. I remember the first one didn't split them and had a "loap", the cylinder firing was paired and uneven, that didn't last long.
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  #15  
Old 06-04-2001, 04:18 PM
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i know someone who owns a BMW bike with a boxer engine. Because the axis of the crankshaft is along the length of the bike, when he revs the engine at a stoplight, he feels a twisting motion along that axis. Quite wierd, according to him.

when the Viper first came out, it had separate sidepipes. They were said to sound like a UPS truck. A very fast one. When they rerouted the exhaust to the back, it sounded more sporting.

VW/Audi have some interesting engines:

- the straight-8 engines of the old racing Audis. Must have had really massive main bearings.

- the VW flat-4

- the Audi inline-5

- the VW VR6 engine

- the VW VR5 engine - this is the VR6 less one cylinder. As if the VR6 wasn't odd enough!

- and to defy all convention, they have those W-engines. Just add a few more, and it will be a radial engine (like those in old warplanes).

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