(car engine roars)
- Through out the CA Corvette's release.
All the hype has circled
around one major buzzword
and that buzzword is MID-ENGINE
and that's sorta old news
but more recently there's also been talks
and leaked footage regarding the upcoming
C8 Z06 using another
very European technology
and that is a flat-plane CRANK ENGINE
and that is super cool that
that is going into an
American mid-engine car.
So today I wanna take a look at the C8
and first explain why
mid-engine is, well it's better,
it just is but there's more science to it
and we're gonna get into it
and then we're gonna
dive into the difference
between a normal cross plane crankshaft
and a flat-plane crank and why
the Corvettes move from one
to the other is actually
a pretty big deal.
It took them over 60
years to pull the trigger
on this technology.
Let's find out why.
(upbeat music)
Now before we get to the nitty
gritty of the C8 Corvette
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Go win you a Corvette.
Talks of a mid-engine
Corvette have been around
since the 1960s but finally
GM has delivered with the C8.
And if we look at the majority
of cars on the road today,
the engine is in the front,
only high end sports cars
from the likes of Ferrari,
Lamborghini and Pontiac
use the mid-engine design.
Waddup my Fiero fans, heck yeah.
So if they use it, there
must be a good reason, right?
Let's break it now.
(upbeat music)
Weight distribution, and
this is where mid-engine
comes into play in a very big way.
Whenever you start
changing the distribution
of weight in a car,
you start to change its center of gravity
and it's polar moment of inertia.
Now, center of gravity
is a pretty basic concept
and I'm sure the majority
of you guys watching
know what it is, but
for those who might not,
it's just an imaginary point in an object
where the distribution of weight
is equal in all directions.
Now, the concept of
polar moment of inertia
is just an extension of
Newton's law of inertia
and it's how difficult
it is to get an object
to rotate around an axis
and here's a practical example
help better understand.
If I take a baseball and
I throw it in the air
and I try to get it to rotate,
it's pretty easy to do that, right?
You can toss it up in
the air and it'll spin.
You can see that it's spinning, right?
It has a low polar moment of inertia.
Now, if I were to take a baseball bat
and it had the same amount of mass,
same point of center of gravity
and I throw it in the air
and try to get it to
rotate, it is much harder.
And that's because it has a
high polar moment of inertia.
The mass is in the ends of the bat
and the farther way from the
axis of rotation the masses,
the harder it is to make it rotate.
So with a mid-engine car,
it has a low polar moment of inertia.
The mass is more centrally located
and therefore it's easier to turn the car.
And in sports cars, that is a good thing.
So by moving the 500 pound engine,
seven and a half feet backwards,
as well as moving the
300 pound transmission
three foot backwards,
it changes the Vets
polar moment of inertia.
Now a bonus in moving the
engine and the transmission back
is that you could place the driver
in a more centrally located area closer
to the center of mass.
Now you know that a low
polar moment of inertia
means the car actually turns in quicker.
Well from a driver experience,
it actually feels like
it's turning in quicker,
which is pretty cool.
(car engine roars)
So what does all those
weight distribution equate to
in the C8, well you get a 40-60 balance,
that means 40% of the car's
total weight is in the front
and 60% is in the back.
When you move the vet's
heaviest component,
the engine further back behind the driver,
you put more weight on the rear wheels
and that added weight
effectively increases
the amount of power you
can put to the ground
and therefore you can
get up to speed quicker.
Not only that,
as you accelerate the weight
of the car shifts backwards,
giving you more traction
and further helping the
car move forward quicker.
Now if we compare the C7 vet to the C8,
the C8 gets from zero to 60 in 2.9 seconds
the C7 with the same Z51 package,
it gets there almost a full
second slower in 3.8 seconds.
Now there is some gearing
changes which cause that number
to be different
but about 50% of that
increase in zero to 60 time
is achieved by getting
more grip to the wheels.
They even designed the
car to run a wider tire
at 305 wide rear tire
compared to the C7 285,
that's 20 more millimeters.
So by managing where the
weight of the vehicle is,
we can improve upon the car's performance.
We can load up the rear
tire and get better traction
and all sorts of driving situations.
We can go into corners faster,
we can pull more G's
without breaking traction.
We can become a mid-engine
American made super car.
But what about if you wanna slow down,
is there any mid-engine
benefit to stopping?
You bet your hot sticky bonds there is.
Braking, in pretty much all cars,
the front brakes do the
majority of the braking
because as you break the weight
of the car shifts forward
in the front, like just like the opposite.
When we talk about acceleration,
when you accelerate,
you move backward, when
you brake, you move forward
and in a front engine car,
this is exacerbated by the fact
that there's already a lot of
weight already in the front.
So how does a mid-engine
layout affect braking?
Well, when you have a more
evenly distributed car in regards
to its weight, each of the four brakes
can then apply braking force
at each of the four wheels
and that creates more
stability during braking.
Also because weight transfers forward,
when you break an a mid-engine layout,
you have less mass upfront
and more weight on the rear wheels.
And in fact during deceleration,
also known as breaking
the C7 carried 66% of the
cars mass on the front
versus 57% on the C8.
And because of that,
the front brakes don't
have to work as hard now
and they actually drop the
size of the front rotors
and made the rears larger,
which is unheard of.
They went from a 13.6
inch front rotor in the C7
to 13.3 inch rotor in the C8
and the rears went from
13.3 to 13.8 inches.
They made the front smaller
and the rear is bigger.
And look at the rotor
sizes in front engine cars,
the front are always going to be bigger
because they have to work hard.
But with the mid-engine car like the C8,
the rears can finally carry
their weight around here.
(chuckles)
So you can see there's
obviously some benefits
to having a mid-engine car
and it might sound like,
oh it's pretty easy.
We'll just move the engine
from the front to the back.
Well actually it's not that easy.
It's actually a lot of work.
I actually got to speak to
one of the chief engineers
on the C8 and there are a
lot of engineering challenges
they had to overcome.
When moving the engine
from the front to the back.
So they didn't have a mid-engine
chassis in their GM fleet
and they weren't going to
go dig up old Fiero joins
dust those bad boys off
and kinda use what they
learned back in the Fiero days.
No, they had to start from scratch.
So they built their
first prototype by hand
and they didn't have a body for it.
So they disguised it
in a holding nute body,
which is pretty cool.
It costs them about $10 million to make,
they use that car as a
test bed for about a year.
So they took everything they learned
from the first prototype
and they built another 15 by hand.
They crash tested five of them.
They got a bunch of
information from those 15
they then a year later built
another hundred again by hand.
Two years after that,
straight off the bowling
green Kentucky plant.
We got our first production
mid-engine Corvette,
the C8 heck yeah brother.
So the C8 team had a bunch of challenges
they had to face along the way.
I mean they had everything thrown at them.
And one of the main things
is they had to still make
and build a practical car.
I mean the majority of people
who are buying Corvettes,
they need luggage space.
They need a spot for their golf bags
and at the end of the day
they made a mid-engine car.
That's from a practicality
standpoint, pretty useful.
So we talked about engine placement
and how they did it better,
but we haven't talked about the engine
and how they're making it
better, CRANKSHAFT! (giggles)
(car engine roars)
Now the engine that comes in the C8
is a 6.2L PUSHROD V8 LT2.
We talked about the
difference between pushrods
and overhead valve engines a few weeks ago
back when we released
episode of the Viper,
but one thing we didn't focus on
is the kind of crankshafts engine use
and when the C8.R Chevy's
race car version of the C8
came out to Daytona this year
to race people's ears perked up
to the exhaust notes coming out the back.
Have you ever wondered why
European high revving V8's
have an engine sound that differs
so greatly from the low rumble of V8's
and American made cars?
I mean they both have eight cylinders.
They both are in a V formation.
They both are four stroke engines.
But an American, it sounds like this.
(car engine roars)
In a European engine, it sounds like this.
(car engine roars)
So what gives.
Well you might jump to
say, well Jerry baby,
they have different exhaust systems
so of course they're gonna sound different
and I'm gonna say, yeah,
I'm sure they got different exhausts.
But what if we take the exhaust
out of the equation huh?
The reason they sound so different is
because of the kind of
crankshaft they use.
The job of the crankshaft is
to take the linear motion of the piston,
that's their up and down moving like this
and turn that into a rotational motion.
So the crankshaft sits in the
bottom of the V in the block
stays right here, right?
And it's connected to the
pistons via the connecting rods.
And along the length of the crankshaft,
are crank journals also called crankpins
and those are the exact spots
to where those connecting
rods attached to.
And the orientation of
those crank journals
determines the type of crankshaft
as well as the firing
order on that engine.
And this is where we can start
to differentiate the flat-plane crankshaft
and the crossplane crankshaft.
Now flat-plane crankshaft
has cranked journals
180 degrees out of phase
from each other,
meaning that every 180
degrees of rotation,
a cylinder fires.
Now if you were to cross
section that crank by drawing
a line through it,
you only need a single plane
to split the crank journals
at their center line.
You need a single flat-plane.
With crossplane cranks,
the journals are 90 degrees
out of phase from each other
and if we apply the same cross
section method from before,
you need two planes
to cut through the center
line of those journals.
And if you look down
the barrel of the crank,
those planes form a cross
hence the name crossplane.
Go tell your mom you just learned
some fricking mechanical nerd stuff.
She's gonna be like, Dylan,
go eat your corn pops.
Now with American made V8 engines,
the most common of the two
crank shaft is the crossplane.
Hemi uses a crossplane
crankshaft, Camaro's used them.
Almost every Mustang uses them.
I know the GT 350 does it,
even the base model Corvette
uses it with their LT2 engine.
Pretty much any American made V8
comes with a crossplane crankshaft.
One of the main reasons
crossplane engines are more common
is due to the fact that they
have a smoother operation.
And to explain this,
let's take a V8 engine
and let's number the cylinders like this,
cylinders, one to eight,
one, two, three, four,
five, six, seven, eight
and if we look at the firing order
in the 6.2L V8 in the C8
Corvette, for example,
it's cylinders fire in
the following order.
It goes from one to eight to
seven to two to six to five
to four to three.
We can see that we go from
one side of the engine
to the other side.
There's a balance between
the two banks of cylinders.
This added in the fact that
there are counterbalances
on the crankshaft to account
for the weight of the pistons
and rods as well as the
forces in between the strokes.
We have a very smooth operating engine.
If we look at the order of the
firing inside a single bank,
they have uneven space firing.
That's what creates
that distinct chunky rumble
sound of a good old American V8
because the firing of
the cylinders is uneven.
The exhaust gas is
leaving, it's also uneven
and it's an exhaust pulses
that make that noise, that
(car engine roars)
Perfect, perfect sound in
American V8, nailed it.
So that is the crossplane.
What's all the hubbub about
the flat-plane cranks?
And flat-plane cranks had
actually been around longer.
From a design standpoint.
They're actually simpler.
Like I mentioned earlier,
flat-plane cranks fire every
180 degrees of rotation,
no matter the firing order.
Flat-plane engines will always
alternate back and forth
between the two cylinder banks.
It's the equivalent of having
two inline fours firing off
and this in turn produces more
efficient exhaust scavenging.
See during the exhaust stroke,
you create a pulse of high-speed
gas leaving the cylinder
flowing down the headers
and this fast moving pulse
creates a pressure difference
and it turn, pulls a vacuum,
pulling more exhaust gas out
and more fresh air in.
And as RPMs increase the air flows faster
and the effects of
scavenging become stronger.
And the more efficient you are with that,
the more power you're make.
It's also what gives the flat-plane crank.
It's unique sound.
That rush of gas leaving the cylinder
has a very on beat order.
This is actually the
best way to visualize it.
Watch and listen.
(car engine roars)
Pretty cool, pretty
American, blah blah, blah.
(car engine roars)
Also pretty cool which one do you like?
Let me know in the comments.
So that's why flat-plane
V8 sound different.
Why are they considered better
than it's crossplane walbro?
Well, one, you have
lower rotating mass due
to less counterweights
needed on the crankshaft.
Now the downside is you
get more vibration issues
because you no longer
have any counterbalances
on the crankshaft.
And as the engine size gets
larger, so does the roughness
and vibration of the engine.
The bigger the engine is,
the more that vibration propagates.
But in end of day, who cares man,
you got freaking race car engine,
race car drivers don't
care about some vibrations.
They wanna go faster,
they want more efficient,
more powerful engines.
And that is what a flat-plane crank does.
Now there hasn't been an
official release from GM
about the Z06,
but there's some footage out there of it
of one driving around the canyons
and it sounds nothing like the base C8.
I got a little insider information
from one of the chief
engineers at the C8 program.
He told me, be quiet.
That remember when they
raced that C8.R in Daytona?
Well homologation rule state
that for them to race that car,
they had to build 300 production models.
So if you read between the lines,
we're getting Z06 with a
flat-plane crank engine baby,
woo dude, Ferrari, we're coming
for your Italian stallion.
(car engine roars)
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Bye for now.
