Today's world of heavy duty diesel trucks is
almost entirely dominated by large inline six, four-stroke engines. But, that wasn't always
the case. As a matter of fact, there was a time, not too long ago, where it was two-stroke diesels
that actually dominated the marketplace. So, today we're going to rewind the clock and take a look at
Detroit Diesel's two-stroke engines and see just what makes them so good. Let's get into. And to
understand where the two-stroke diesel came from, we first need to rewind the clock and take a
better look at where Detroit Diesel came from. Back in the late 1920s and early 1930s, General
Motors was in a good spot to buy new companies, as the stock market crash of 1929 massively
devalued many companies in the automotive space. Now GM was looking into a handful of different
companies, but ultimately they wanted to buy diesel engine manufacturers at that time, that's
specifically what they were going after. They even had the opportunity to purchase Cummins
at this time, but ultimately passed on them to purchase a company known as Winton, as well
as Electro-Motive Company. It's crazy to think how much different things would have been if
GM had bought Cummins all the way back in 1929, but as they say, hindsight is 20/20. Between GM,
Winton, and Electro-Motive, and a smart inventor named Charles Kettering, they took existing Winton
two-stroke diesel engines used for yachts and improved upon them massively, mostly working
on perfecting the unit injector. And by 1938, Winton became the Cleveland engine division with
the goal of just continuing to produce marine and stationary power applications. And one year after
forming that new engine division, they decided to take all the R&D that they had already done
on these ginormous two-stroke diesel engines, and shrink it down to a smaller platform. One that
wasn't meant for marine, locomotive, or stationary use. And to do this, they needed to put it under
a new company, so they formed a new division known as Detroit Diesel. And that takes us to
Detroit Diesel's first ever engine, the Series 71. And although the Series 71 was based on the
research and development of the Winton two-stroke diesel engines, the Series 71 wasn't just a
shrunken down version of those engines. Rather, it was an entirely new engine platform, something
that we had never seen before. And with this all new Series 71 engine platform, it initially came
in three different sizes. You could either get a three cylinder, a four-cylinder, or a six
cylinder, known as the 3-71, 4-71, and 6-71. And by 1938, Detroit Diesel had massively ramped
up production of this new engine series and sent about 700 units, 700 engines, over to GM's Truck
and Coach Division. And then one year later, in 1939, they went ahead and sent Series 71
engines to vary suppliers to test out and try for themselves. Fast forwarding a little bit, the
Series 71 was used all across World War II and by 1944, a whopping 62,000 of these engines were
produced. After the war, though, things really started to shift in America. Where transporting
goods across the country was once almost entirely done by rails and rail cars, things started
to shift over to over-the-road trucks as they preferred way of transporting goods around the
country. And this happens to coincide with the Federal Aid Highway Act of 1956, which massively
improved intercity travel as well as interstate travel. By then, Detroit had also introduced
two other engine Series. The Series 110 and the Series 53. Both of which were also two-stroke
diesel engines. Alright, that's enough about where the two-stroke diesel engine came from. It's time
we take a look at how this thing actually works, because it's pretty interesting. Now, rather
obviously, a two-stroke diesel functions quite a bit differently than a four-stroke diesel, as
the name implies. With a four-stroke diesel engine or just a four-stroke engine in general, there's
going to be an intake stroke, compression stroke, ignition stroke, and an exhaust stroke. But,
with a two-stroke diesel, intake, compression, ignition, and exhaust all happen in two strokes
and one rotation of the crankshaft, rather than four strokes and two rotations of the crankshaft.
In this diagram here, you can see how this works, with the intake port of the cylinder located
at the bottom of the cylinder on the wall, rather than an intake valve at the top of the
engine. But, this presents a big problem already. With the intake stage happening at the bottom
of the stroke, there is no vacuum to pull air into the cylinder like a four-stroke engine does,
which means two-stroke diesels require some sort of forced induction just to operate normally.
And while there is no intake valve on the head, there is still an exhaust valve on the head, as
well as the fuel injector. And the way this works, by effectively just cutting the strokes in half,
they do the the intake and the exhaust stage at the same time. As the piston reaches bottom dead
center of the combustion cycle, the exhaust valve opens around the same time that the intake port is
revealed, with air being pushed into the cylinder by forced induction also helping to push out the
exhaust. All right, so it's at this point in the video, you know where Detroit Diesel came from,
you know where the two-stroke diesel came from, and you know how it works. The question is why
even bother with this? What is the point of a two-stroke diesel as compared to a four-stroke
diesel? For one, the two-stroke diesel design is not only simpler with fewer moving parts,
but it is also quite a bit lighter, smaller, and easier to manufacture. Granted, the weight of
the engine isn't particularly important for over the road truck applications, but it is still a
benefit worth noting. As a side note, lightweight is a very very loose term here, because the
(intially) smallest 71 Series engine, the 3-71, that little three-cylinder engine came in at over
1500 pounds. I think it's safe to say this is not something you're going to be swapping into your
Miata. And with less moving parts to fail, there also comes the benefit of reduced maintenance,
at least in theory, which is a massive plus, because when your truck breaks, the money
stops coming in. And because the weight is low, the physical size is small, and there are twice as
many combustion events happening per engine cycle, the power to weight or power to physical size
ratio of a two-stroke diesel, is far past anything a four-stroke diesel could offer at the time. And
although you could argue this is less of a benefit than it used to be, having the ability to run on
different types of fuels, including heavy fuels and low quality fuels is a pretty big advantage,
particularly in certain applications where fuel availability or quality is a concern. And with
these advantages, it's pretty clear to see how the 71 Series, how the Detroit Diesel two-stroke
engine, in general, became so popular. It was just simply good. And it became even more popular after
Detroit Diesel introduced a new variant of the 71 Series, which is the V variant. With this new
V layout, Detroit Diesel was not only able to offer engines with more power than ever before,
but also a variety of different displacements, giving you more choices than ever. The options
for the v71 include the 6v71, 8v71, 12v71, 16v71, and much later on, the 24v71. So, if the
two-stroke diesel is so good. It's lightweight, it's compact, makes decent power, has loads of
different displacement options, where is it now? Why aren't we seeing it on the road anymore? The
answer to that, can be summed up in a single word: emissions. Two-stroke diesel engines, including
those from Detroit Diesel, were faced with some serious challenges in meeting stricter emissions
regulations. Keep in mind, the EPA wasn't even formed until 1970. So the idea of reducing or
even limiting emissions of any given engine, wasn't really a thought or concern. And with a
two-stroke diesel engine, the scavenging process can result in much higher emissions of pollutants,
such as particulate matter. There's also the issue with fuel efficiency at low loads with two-stroke
engines being worse than comparable four-stroke engines, which simply means two-stroke engines
consume more fuel and output more emissions at idle or low load conditions. Two-stroke diesel
engines also typically have quite a bit more oil consumption than four-stroke diesel engines,
which again, is not great for emissions. And as emission standards became more stringent after
the creation of the EPA under President Nixon, meeting these requirements became increasingly
difficult for Detroit's two-stroke engines, until they eventually just couldn't meet the on-road
emissions restrictions and had to be phased out entirely. So, that brings up a good question here.
If the two-stroke diesel engine has a lot of pros: it's small, compact, makes a good amount of power,
and the only con is really the emissions output, couldn't this be modified with modern technology
in order to bring it up to today's emission standards? And the answer is not really, no.
Detroit did make advancements in the emissions output of their two-stroke engines by adding
electronic controls, but eventually it just wasn't possible to keep up with the demands of the
EPA. The underlying issue is that with two-stroke diesel engines, the combustion configuration
allows unburned fuel to pass out of the exhaust port before the port is closed, resulting in
excessive emissions output. And as long as that underlying design exists in the two-stroke engine,
it's just simply not going to meet the EPA's demands, it's just not possible. And it's much
of the same reason that two-stroke gas engines are kind of being phased out, again, thanks to
the EPA with their emissions restrictions. So two-stroke dirt bikes, two-stroke power tools like
a leaf blower, stuff like that, it is slowly being phased out, again, because two strokes are just
really bad on emissions output. That being said, a two-stroke diesel engine is still feasible to
use in off-road applications where you can sort of get around emissions testing in some situations,
particularly for something like a tractor powered by a Detroit diesel engine. But, for on-road
applications, there's really no getting around the EPA's requirements, unless you want to do
it illegally. And I don't say this very lightly, but I think it's safe to say that the Detroit
Diesel two-stroke, the 71 Series, as well as their other series of engines, are some of the
most important engines in America's history. With their massive popularity and the shift
from rail cars over to over-the-road trucking for transporting goods across the country,
these engines quite literally help to build America into what it is today. And partially what
makes the two-stroke diesel engine so interesting, is the fact that no other companies from that
time frame, Cummins, Caterpillar, they weren't even competing with the two-stroke diesel engine
because they were just making four-stroke engines. They had no interest in doing this two-stroke
over the road trucking engine. At one point, Detroit Diesel quite literally controlled around
30 percent of the market share for over the road truck engines and built an absolutely
massive amount of these two-stroke engines, with loads of them still in use today, although
the remaining applications are generally not over the road trucks. Interestingly enough, though,
somebody who did copy Detroit Diesel and made a two-stroke diesel engine is the Soviets. Now, you
have to remember Detroit Diesel worked with the military to supply their two-stroke diesel engines
for a variety of different military applications, the Soviets caught on to this, copied it, and
did the exact same thing, copying the 4-71 and the 6-71. Now, as a side note, an industry which
is still using two-stroke diesel engines, although not engines built by Detroit Diesel, is the Marine
industry. And a really interesting feature for these massive marine engines is that there is no
gearbox, which means if they want to turn the prop in reverse, they just shut the engine off and
turn it back on but with the engine spinning in the opposite direction. That is definitely not
something you can do with a four-stroke engine, at least not easily, and it's a very cool
feature for a two-stroke diesel engine. So, although Detroit Diesel's two-stroke engines
lasted for a significant amount of time and quite literally helped to build America into
what it is today, powering countless applications from military to over-the-road trucks, the
introduction of emissions restrictions from the EPA was the beginning of the end for these
engines. Two-stroke diesels just simply couldn't meet the EPA's demands, and that's not necessarily
a bad thing, because Detroit Diesel was able to move on to very very good four-stroke engines
and had a lot of success with those, in fact, you could argue that they had more success with
their four-stroke engines than their two-stroke engines, but regardless, it's safe to say we're
probably not going to see two-stroke diesels ever come back to over the road trucks. Let me
know your thoughts down in the comments below, if I missed anything, anything you want to add,
drop it down there. While you're down there, smash Thumbs Up Button if you enjoyed
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videos, we even have a history lesson on Detroit Diesel if you want to check that out, learn more
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