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Trucks Of The Month
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BY Will
Wills
My
first real taste of diesel came when I was in the Marines. I drove
HMMWVs and CUCVs with naturally aspirated 6.2s, and 5-tons with huge
naturally-aspirated 14-liter Cummins engines--a whooping 240hp. I was
not impressed. Besides that, when I was a teenager General Motors was
playing with the gasoline conversion Oldsmobile engines and they were
developing a reputation for being weak, smoky and unreliable. How
foolish it all was.
In
the late eighties Dodge made the momentous step of buying Cummin's
turbo-diesels for its Power Wagon pick-up and people's eyes started to
open. They were a few years behind GM and Ford in offering a diesel in a
full-size pick-up, but man, what a diesel. Suddenly Ford and Chevy were
scrambling to keep up. Both were suddenly offering a dealer installed
turbocharger from Gale Banks Engineering, and then, eventually,
engineering their own turbo-diesels. The torque wars were on.
My
wife received her Masters in Electrical Engineering (controls) and got a
job with Cummins Engine Company (now Cummins, Inc.) in 1997. And it
wasn't until then that I really began to learn something about diesels.
We moved to the Columbus, Indiana area where you are hard pressed to
find a heavy-duty pickup with a gas motor. I live on a road where on a
summer weekend, dozens of diesel pickup haul large fifth-wheel horse
trailers down to Brown County State Park. Fifth wheel travel trailers
and diesel-pusher motor homes fill the highway, embarrassing anything
still running gasoline. When you are towing a Ranger on a trailer behind
a fuel injected 5.7 gas motor (like I was) and a PowerStroke with three
conversion vans on it goes ripping past you up a hill, you have to
wonder: what is going on here? What am I missing? So, when I decided I
need a tow vehicle, I decided to join in and find out.
First,
diesel and gasoline motors are two entirely different beasts. It isn't
enough to think of them as spark ignition, compression ignition. You
have to think of them as stoichemetric and non-stoichemteric. In other
words, a gas motor has to run a precise mixture of gas and air or it
will run lean and burn up. A diesel isn't bound by that limitation. The
other limitation with gasoline is that the fuel is much more unstable.
Too much pressure and it will explode causing detonation (knocking on
hills, for example). Add a turbocharger to an engine that won't knock
and isn't restricted by stoicheometry and you have the potential for
huge torque. But there are more advantages.
Diesel
engines extract more energy from their fuel than gasoline motors. Part
of this is due to the higher compression (about twice as high in most
instances) which forces the oxygen and carbon molecules closer together
for a more complete burn. Part is also that the fuel is about a pound
heavier than gasoline per gallon and simply contains more energy per
unit volume. And part of it is that there is lots of oxygen to make sure
the fuel is used up as the balance isn't delicate since there is no risk
of going lean and burning the motor up. In short, a diesel has a
much hotter combustion, and expends a higher percentage of its heat in
turning the crankshaft.
The
real magic is in the turbocharger. As I said above, I had the impression
that diesels were dogs because all of the ones I had driven were
naturally aspirated. Turbocharging is made for diesel engines. It is a
match made in heaven; well, just about. A diesel uses it's turbocharger
to provide air to burn the fuel up, and for cooling the combustion
chamber. A modern diesel pickup engine pushes about 32psi of boost at
maximum torque, needing about half of that pressure for power. The rest
of the air is to help make sure the truck passes emissions. Aftermarket
chip companies simply have to turn up the fuel to make more power. A
Cummins 24-valve 5.9 will safely survive 950ft# of torque, and can make
it on it's own fuel system. It just won't pass emissions, and the
drivetrain would die a grim death. So, while gas engines are approaching
one ft# of torque per cubic inch (if they don't start detonating--load
one up on a hill and see how long you can keep the pedal to the mat),
diesels are running 1.5 ft# per cubic inch and are only limited by
emissions concerns. A field day for the aftermarket as they can deliver
around 2.5ft# per cubic inch.
But
you have to put a load on it to really feel the difference. My truck has
about the same horsepower as a fuel-injected 460, and maybe 30ft# of
torque more. Empty, the 460 might beat me as it has a wider rpm band.
Loaded, no way. The turbo-diesel does not feel like the throttle is
going out from under you as the engine loads down. The governer dumps in
more fuel, making more heat, the turbo spools up and the thing feels
huge the whole way up. And it ain't even working. You really have to try
it to see. Awesome. Once you do, you won't go back to gas. And my truck
is WAAAY behind the new diesels.
So
what is the problem here? Why aren't we driving Ranger's with diesel
engines? We could be getting almost twice the fuel economy, making tons
of useful torque everywhere and making cool whistling noises from our
turbos. It would only take a 2.5 liter turbo-diesel to embarrass a SOHC
in the pulling department. Not only that, but there is no way you are
going to stall the engine while rock crawling, and it would have awesome
control offroad. How about a 150hp exhaust brake for decending steep
grades? Am I dreaming?
Part
of the reason we are still saturated with gasoline is the
disillusionment we all received with GM's gasoline coversion failures.
It left a long-lived bad taste in our mouths. Not only that, but since
the market was destroyed by the lack of power and unreliability, no
money was put into developement. The International 6.9 and 7.3 and the
Detroit 6.2 that was sold naturally aspirated for years were not exactly
the top choice for power hungry haulers, and the manufacturers didn't
think people would shuck out the extra $2,000 per truck to get a
turbocharger. People with big loads to pull were more likely to check
the big-block box. Then the emissions problems came on strong. The
ever-tightening EPA regulations even chased the EGR equipped 6.2/6.5 out
of the under 8,500# pickup truck market. All of the diesels sold today
are in over 8,500# trucks as the regulations are looser in heavier
trucks.
But,
take heart: things are in the works. Technology is catching up. The
turbocharged heavy-duty pickups have won people over to the reliabilty
and power of diesel. Rumors are flying that we will soon get some
light-duty pickup engines and hopefully, eventually, Ranger sized ones
as well. I can tell you one thing: I'm ready. I am definately ready.
~TRS
Have
a rant? E-mail me at wwills@iquest.net,
or contact me via PM, and I might just let you put it here!
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