- What do a $1.8 million super car, a group B rally monster, and this tiny hundred horsepower
hatchback have in common? They're all twin charged baby. They have both a supercharger
and a turbocharger. A true KFC double down sandwich of power. This decades old design
could be making a comeback. So today we're going to figure out why you would want to double down on forced induction and why so few cars have
ever been twin charged in the first place. Turns out mo' charging might
just mean mo' problems. Biggie smalls, 2021. He's still alive. I don't know what they want from me. It's like the mo' charging we come up and the mo' problems we see. (bouncy music) Thanks to K&N for
sponsoring today's video. It's officially garage season. Which means it's time to start spending countless hours working on your cars and spending a ton of money, constructing your own upgrades
like this custom air filter. I call it the fast air
recirculation transmitter. Smoke means it's working. - Why not just use a K&N filter, it's way easier than that. - I'm sorry, but it can't be easier than this. Air gets sucked into these
dual unnecessary duct. Gets passed to this nice multiple
precise oxygen sensor down into the elastic waste washer and back into the box for a farrow integrated injector. - Yeah or you can just go to a K&N filter. They are easier than that. Honestly, they work way better. And K&N was started in
a garage with two dudes in Riverside, California, 50 years ago. So, you know their products are engineered for people who love garage season. They offer air filters, cabin air filters, oil filters, air intakes,
electronics, and much more. - Sure, but do they make
custom ones for your vehicle? You know, mine's custom
because I use plywood and I use my grandma's fan for it. - Yeah K&N actually designs these to custom fit specific makes and models and their upgrades are
designed to be easy to install, to make your car run faster, run further and run cleaner. And we use K&N filters on
a bunch of our donut cars and even on our personal cars. It's what I was running on
my S14 back when it ran. So head over to knfilters.com/donut for some special discounts today. - All right. I'll admit I'm impressed, but this K&N have an oil hub
filter utilization contraption? - Yeah, as I said, just seconds ago, they make oil filters. Here, this one's for you. - You really have thought of everything. 1985 saw the NBA debut of Michael Jordan, the original Nintendo hit US shores and the first production engine to use both a turbocharger
and supercharger was put in a car, which is 1.8 liters of displacement. That engine made 500 horsepower and was in the Lancia Delta S4. It won five out of the 12 WRC rallies that entered in that year. And the 35 years since then there have been just eight
twin charge production engines, but three of those have
debuted since 2018. But why would you need both
a turbo and a supercharger? Why not just have a twin
turbo or a twin supercharger? Does that even exist? Well, to understand why there
are so few twin charge engines and why we may be seeing
more on the horizon, we first need to understand
what forced induction does and why you would use
it in the first place. Every internal engine
needs a healthy diet of air and there are two ways to get it. Some engines are naturally aspirated, these other almighty,
but gentle whale sharks, drifting along lazily scooping up air, but others, they use forced induction. These are like great whites
charging around the seeds, gobbling up as much air as they can to feed their ceaseless hunger. That extra air is forced
like this shark analogy. We could have chosen anything else, but we chose the animals in the water. Doesn't matter. Okay, now it's forced into the engine by an external compressor, which raises the density
of the intake charge. Intake charge is the mixture of air and fuel entering the cylinders. The amount of oxygen in the charge determines how much fuel an engine can combust. The air entering a
naturally aspirated engine has the same density as
the atmosphere around it with natural aspiration the
only way to get more air into cylinders is to
increase their volume, known as displacement. But with forced induction, a compressor raises
the intake air density, creating supercharged air
with more oxygen by volume. The amount the air density
increases is the boost pressure combine boost with more fuel, and that means bam, embryo,
like glacey more power. In other words, by increasing the density of the air, you can burn more fuel without
needing a larger engine. Exactly what you want, if you're designing a car with the limit on engine displacement, like they have in the WRC, or if you want the fuel economy and emissions of a small engine, but with more power. Now, the two most common compressors are turbochargers and superchargers. Each have benefits and drawbacks and twin charging uses the
advantages of one of those to make up for the drawbacks of the other. So to understand how
they can work together, we need to look at the biggest
difference between them, how they're powered. A turbocharger uses the engines
exhaust as a power source, exhaust gas spins a turbine, which is attached to an impeller. Impeller draws more air
into the engine's intake to create boost. And the bigger the turbo is, the more boost it can make, but turbos, especially big turbos have a couple of drawbacks. One of them is heat like me
when I'm on the dance floor, cue me dancing on the dance floor. You see how hot I get. Increasing intake pressure
also increases temperature and hot air has less oxygen
by volume than cold air. Since the whole point of a turbo is to increase the amount of
oxygen in the intake charge. Many turbo systems will
include an intercooler, which works like a radiator. The charged air is routed
through a metal panel with lots of fins. All that surface area transfers heat from the pressurized
air to the atmosphere. That's great for lowering
intake temperature, but it increases the complexity and weight of the turbo system. It also adds internal
volume to the intake. Filling that extra space with
pressurized air takes time. That creates a power delay
from when you mash accelerator as boost pressure built into the system, something referred to as turbo lag. Oh you got turbo lag dude. Dude I never had a turbo lag. I don't know what you're talking about. Now lots of times turbo lag is confused with something called boosts threshold. That's the minimum speed at which there's
sufficient exhaust pressure to spin the turbo fast
enough to create boost. With a small turbo, the boost threshold can
be as low as 1500 RPM, but bigger turbos might
require engine speeds of 4000 RPM or more. The turbine itself will be
spinning 10 to 30 times faster than the engine. And some turbos can reach
speeds over 280,000 RPM. That's like this fast. Generally bigger turbos make more boosts, but with a higher boost threshold. It takes power to push
exhaust past the turbine and below the boost threshold, the turbo actually reduces the amount of power being sent to the wheels. So how do you deal with
something like that? What do you do? Oh one way is to add another
force induction device that isn't powered by exhaust pressure. And in that case, that's a supercharger. You can power a supercharger
with electricity, but that's pretty uncommon because it comes with
its own set of problems. We made an entire episode about it, check it out here if you want to know more. Instead of electricity or exhaust gases, a typical supercharger gets power from the rotation of the crank. And there are three common types. You've got a centrifugal,
you've got a roots, you've got a twin-screw. Centrifugal superchargers
operate a bit like a turbo, but replace a turbine with a
pulley driven by the crank. Like a turbo, these
have a boost threshold, typically needing an impeller
speed of 30,000 to 60,000 RPM. To achieve that, centrifugal superchargers
use a set of gears to multiply the crank's rotation. That means as crank speed increases, there's an exponential
increase in impeller speed, but below the boost threshold, they simply aren't spinning
fast enough to do anything. And that means a centrifugal
supercharger won't make up for a turbo's lack of low RPM punch. Pop, pop, pop. So for twin charging, you need a roots or
twin-screw supercharger because both are positive
displacement superchargers. That means they flow
the same amount of air for every rotation of the crank from idle all the way to red line. And that means no boost threshold. Because these superchargers
are pumping the same amount of air regardless of engine speed, they can be measured
by their displacement, just like an engine. So two liter roots or
twin-screw supercharger moves two liters of air for
every rotation of the crank. A roots supercharger uses two rotors with three or more lobes that mesh together as they
rotate in opposite directions. The space between the
lobes is filled with air on the inlet side of the supercharger, and that air gets forced
out on the discharge side, into the intake manifold. The air isn't compressed inside
of the supercharger itself. It's simply blown by the
compressor into intake. So these are sometimes called blowers. Roots blowers are simple and reliable, but they have some drawbacks as well. They tend to be heavy, produce a lot of heat and
take up a lot of space. Because they're driven by the crank, they're also parasitic
like that worm in my belly, drawing power from the
engine to spin the rotors. Those rotors also don't seal perfectly. So air leaks between them and that inefficiency
reduces boost pressure. Twin screw superchargers
use two screw shape rotors with a male and female side
that mesh more completely than the rotors in the roots blower, meaning fewer air leaks. Those screw rotors also
compress the air inside of the supercharger itself. Meaning they're more
efficient than a roots. They're also smaller and lighter, but because of their tighter tolerances, they require more
precision to manufacture. And they're usually more expensive. Since they always provide
the same volume of extra air with every rotation of the crank, the extra power from a positive
displacement supercharger is available at idle. But the big problem is they
can never make any more boost than that. And they can't reach the same peak output that a turbo can. A turbo will be more capable at high reps, but at the cost of low-end
power below the boost threshold. So at this point, you guys figured out why you might want to use both of these. You get the best of both worlds. Supercharger can add boosts from idle up to the turbos boost threshold, and then the turbo can take
over to make even more power all the way up until redline. The supercharger can also
fill in for the turbo while it's spooling up
to reduce turbo lag. So twin charging is the
best of both worlds. But like everything that seems to be great as you're approaching it
with that analytical mind, there are some problems. First problem is I need to go real quick to change my underpants
cause I let something out and I left fart out
and something came out. What are some of the actual problems? Well, you've probably already guessed what some of those might be because we talk about them in
nearly every episode of B2B, when we're discussing some
new piece of technology. Mass, complexity and the cost. A turbo requires a bunch of
extra stuff under the hood. You need a complicated exhaust manifold. You need extra intake
plumbing for the intercooler, which needs to be placed somewhere that isn't getting cooked by the engine and the turbo itself. That all takes up space
and it adds weight. Adding a supercharger does the same thing. You need an extra pulley and
a belt coming off the crank. The supercharger is usually mounted right on top of the engine,
increasing its height. And if you want to cool that air, you're probably going to
have to mount the intercooler in the worst place possible, directly between the motor
and the supercharger. That means running lines
for liquid cooling. So using both types of force induction means those systems have to work together. Twin charge incidents have two partially
overlapping intake pass, complete with sensors to
detect air flow in both and an ECU program to
switch between the systems that requires a clutch to
disengage the supercharger pulley at high revs and solenoids
and valves to seal the part of the intake where the turbo takes over. That's one reason why so few D-holes twin
charge their engine. Well, if you're D-hole, you're part of the donut underground our members only
subscription-based service, you get a bunch of extra content. You get shirts, you get stickers. Click that join button right below. You can even get in the
discord chat with me. I'm a fellow D-hole. What's up my D-holes,
D-hole, D-hole, D-hole. And the other big reason is the cost. Volkswagen made one of
the few mass produced twin charged engines
with their 1.4 liter TSI. They put it in the Golf, Jetta and many other small cars as a replacement for a two liter naturally
aspirated engine. The result was more power,
more torque, less weight, better acceleration, better fuel economy and reduced emissions. Earning Volkswagen numerous
engine design awards between 2006 and 2011. But then the accountants
figured out that getting rid of the supercharger would save
them over 10 million bones. Replacing it with an
engine that was turbo only wasn't that much worse. So you got the axe. There have been just
eight production engines that have been twin charged
in the history of engines. It's not very many because there's a lot
of engines out there. I guess if it was a good idea, everyone would be doing it. But three of those eight have appeared in the last three years. Audi, Land Rover and Mercedes
have all recently jumped on the twin charging bandwagon. What makes this new generation
of twin chargers interesting is that the supercharger is electric. This is a musical episode. The problem with electric superchargers has always been providing
enough electricity to make them spin fast. The Audi, which is a twin charged diesel needs a special electrical system, just for the supercharger. But the Land Rover and the Mercedes have an internal combustion engine and a hybrid system with big batteries to power electric motors, and more than enough for
electric supercharging too. Combined those systems are
good for around 400 horsepower. So I guess twin charging
ain't dead just yet until electric completely
kills the engine part of that twin charged engine. (melancholy music) - Hey friend, I know where you're at. You forgot to get a gift for
the donut fan in your life, and it's too late or
anything to be shipped. Well, you're in luck because
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things still get to people. And each of them are designed
after an 80s credit card, which is a genius idea that I came up with in literally three seconds. So head on over to donutmedia.com and pick up your perfect
stocking stuffer today. - Thank you guys so much for
watching this episode of B2B. What do you think you
guys got any homegrown, homemade twin charging systems out there? Leave a comment down below. Let me go see, I'll go. I'll go Google it. I'll go search for it. If you could please hit that
Like and subscribe button that lets us know that we're doing good. I don't know if the
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