- Straight-six, V6, inline-six?
Slant-Six?
Six-cylinder engines!
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Alright. Today we're talking about
inline-6 cylinder engines and the V6 engine.
Is one superior to the other?
The answer's the same as if you ask me
what kind of underwear I prefer, boxers or briefs.
And I'll just tell ya,
Depends.
(cackling)
First off, there's the inline-six engine.
Dutch manufacturer, Spiker, built the first one
for their all-wheel drive Spyker 60 horsepower
race car in 1903.
Sometimes we call em straight-sixes.
Or when referencing old Chryslers,
they're known as Slant-Sixes
cause they're installed at a 30 degree angle.
Today, the Nissan RB, (engine revving)
Toyota 2JZ (engine revving)
and BMW S54 engines (engine revving)
are the best known inline-sixes around.
But why are they
such a big deal? - Yeah!
- Hang on and I'll get to it.
For one, having all the cylinders in a row
makes an inline-six inherently balanced.
In a piston engine, there's a lot of moving parts.
We know this.
The pistons move up and down
and they have inertia.
And every time they change direction
they exert what are called primary forces.
That translates into engine vibration.
Primary means that these forces happen
only once per revolution
of the crankshaft.
Secondary forces are also related to
the pistons' up and down movement.
But they're just a little bit different
because of where they're exerted.
If the piston starts at top dead center,
then the first 90 degrees of crankshaft rotation
the piston travels a little bit further
than half way through its whole stroke.
That's because of the way the connecting rod
attaches the piston to the crank.
From 90 to 270 degrees of crank rotation,
the piston doesn't travel quite as far.
Then, from 270 to 360 degrees,
it goes a bit further again.
Since each portion of the movement
happens in the same amount of time,
that means the piston is traveling a little faster
in the top half of its stroke
than in the bottom half.
These different speeds
are the secondary forces
that cause an imbalance of the engine
which means more vibration.
Well an inline-six operates
like two inline three-cylinder engines
placed end to end.
The pistons move
as mirror image parts.
With one and six, two and five, and three and four
always moving in tandem.
When one pair is at top dead center,
a second pair is moving downward,
and the third pair is moving upward.
That cancels out the primary forces.
Then, each of the crank throws
is separated by 120 degrees
which cancels out the secondary forces.
The result is that the engine naturally runs smoothly.
Oh, and uh, it sounds pretty good too.
(car engine revving)
Another advantage to a straight-six
is that putting all the cylinders in a line
is a really simple layout.
It only needs one basic engine block,
one cylinder head,
one valve cover,
and one set of valvetrain components.
Since it's naturally balanced,
there's no need to add balance shafts
or anything extra to smooth it out.
That makes it both a little cheaper to produce
and much easier to work on.
Straight-Sixes are long and tall engines
which can be both good and bad.
A car's gonna need a pretty long nose
to accommodate the engine.
Not a bad thing if you're building
a pretty good-looking sports car.
Or if you're singing the Humpty Dance.
♪ The The Humpty Dance is your chance to do the hump ♪
This shape also leaves a lot of extra space
along the sides of the engine bay
for performance enhancers
like turbos and exhaust headers.
On the other hand, the long vertical shape
of an inline-six
means it's got a slightly higher center of gravity
than a V-shaped engine
and a bigger, longer crankshaft and camshafts are gonna
try to flex more than shorter ones would.
But there've been so many advancements
in modern engine technology
that that stuff really doesn't matter too much anymore.
That length also means
that it's also almost impossible to use a straight-six
in a front-wheel drive car.
(high rev engine motor)
When a straight-six engine's turned sideways
there's almost no room left to connect
the transmission in the front axle.
That's why most front-wheel drive cars
have more compact inline-fours or V6s.
On top of that, most manufacturers
are in the business of maximizing their profit
so they do cost saving things like
sharing engines across multiple platforms.
The engineering effort required to adapt a straight-six
into an existing chassis
or develop something completely new
just for one especially cool engine?
It doesn't fit on that old bottom line.
The fact that the inline-six
is so silky smooth
and is a less common engine,
it makes it even more appealing.
(engine revs) (tires screech)
Alright next up let's talk about
the more common V6 engine.
A V-layout is more complex than an inline engine.
And a V6 didn't really appear in mass production
till the Lancia Aurelia in 1950.
A V6 is basically
two inline three-cylinder engines
sharing a crankshaft,
and placed at an angle from each other.
Usually 60 or 90 degrees.
In this configuration
the primary and secondary forces
that cause engine vibrations
don't all cancel each other out.
So V-shaped engines
tend to run a little rougher.
To make a V6 run smoothly
counterweights are needed
to balance the unwanted inertia
and reduce vibration.
Weight is added to the crankshaft
to counteract primary forces,
and balance shafts are sometimes needed
to counteract secondary forces.
Plus, the larger the engine displacement gets,
the more counterweight it'll need.
This adds more complexity to the
development and production
of V6 engines.
Because the two banks of cylinders
aren't laid end to end,
a V-shaped engine
can be way shorter than an inline.
Heck, a V6 can be shorter than an inline-four.
That makes it easy to package
in almost any car.
And it works well for the transverse
front-wheel drive platforms
that are so popular in modern cars.
It also means it won't cost manufacturers much extra money
to offer a punchier V6 option
in addition to the typically lower power
but similar length four bangers.
Here in America where people herald the phrase,
"There's no replacement for displacement",
V-shaped engines (engine revs)
really took off in popularity because
you could squeeze in the extra cylinders
making extra displacement
while taking up much less longitudinal space.
However, the wider V shape of the engine
leaves less room along the sides
for turbos and things like that.
But that doesn't stop manufacturers from doing it, though.
The Nissan GTR and the new Acura NSX
are notable examples of sweet turbocharged V6s.
But they're more tightly packed deep down in the engine bay.
And that makes working on them
even more of a headache.
Oh, and another thing that makes maintenance
a bigger headache on a V-shaped engine
is that there's gotta be a set of stuff
for two banks of cylinders, instead of just one.
That's two sets of camshafts,
two cam sprockets,
two valve covers,
two cylinder heads,
and two exhaust headers.
It also needs a much longer
timing belt or timing chain.
So that's more stuff to manufacture
and more stuff to deal with
in terms of maintenance.
Still, the V's shorter length
makes it so much easier
to transplant into multiple car platforms
while maximizing interior space,
that it's by far the most popular
six-cylinder option today.
That doesn't mean the inline-six is dead, though.
In fact, Mercedes is actually
replacing its V6 engines
with a new turbo-charged
three-liter straight-six.
With efficient inline-four cylinders starting to become
the base engine of choice,
well, moving to a closely related,
inline-six makes sense from a production standpoint.
So, just like my favorite movie, The Longest Yard,
each engine has pros and cons.
Ultimately it comes down to preference
and what you're planning to do with the dang thing!
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