[Vwdiesel] Turbo vs. Non-turbo [was My TURBO test (more scientific)]

[James Hansen]

> Please correct me if I am wrong about any of the below. I have also
> noticed another very significant difference above and beyond the
> horsepower/torque increase when turbocharging a diesel, as I own 4
> diesel vehicles, a turbo and non-turbo 6.2l suburban, and a turbo and
> non-turbo 2.4l (VW engine) volvo. A turbocharged diesel responds much
> more like a gasoline car, because the turbocharger spins up quicker than
> the engine, and causes the motor to rev much more freely, and is able to
> utilize more throttle without just converting the extra fuel to soot. On
> a mechanically injected non-turbo diesel at lower rpms there is a point
> (between half-full) throttle where more throttle just makes it smoke
> more, but won't put out more power, because there is no more air. A
> Turbo Diesel seems to produce maximum boost only at full throttle at
> these rpms, and will therefore respond to the entire range of throttle
> input, just like a gasoline engine with a throttle body.

Not really.  It is dependant on a number of factors.  TIming, fuel settings,
boost enrichment, camshaft design which dictates at what rpm your torque and
hp will peak, etc. Mine makes full boost any time you press on the pedal.
It's all in the setup.

 A non-turbo
> diesel revs and responds so slowly, that I think under a light enough
> load, a gasoline engine with less horsepower would outperform it


Depends on the definition of perform. Quarter mile times or how far you go
on a gallon of fuel. The diesel will win the latter hands down.


, while
> a turbo diesel responds much more like a normally aspirated gasoline
> engine.

But that is not the reason why the turbo is there...
It all boils down to VE, or volumetric efficiency.  The higher the VE, the
more you can get your engine to do in terms of work and efficiency. If a
greater percentage of the cylinder swept volume is filled in a given intake
stroke you have potential to burn more fuel, to make more power, or to burn
the same fuel more efficiently and completely.



 A normally aspirated Volvo 2.4l Diesel puts out 80 horsepower,
> while a Jetta TDI puts out 90, only 10 horsepower more, in cars that
> both weigh about the same. The TDI feels like it has twice as much
> power, while if they were both pulling heavy trailers and had to rev
> very slowly, I would assume that the TDI would only be about 15% faster.

Other factors at work here.  Cam design, timing, injection timing, advance
etc.  Peak torque in a tdi design cam at 1800 rpm.  Not so with your volvo.
You have to turn faster to get peak, around 2800 or so IIRC.   The butt dyno
is pretty poor rating system actually. If you do the trailer pulling
scenario, if you could get each runnig at the peak torque rpm range, you
would be in the sweet spot for efficiency and power.


> I wonder if that could account for some of the very low horsepower
> readings on non-turbo diesels?

Low VE.  Low power.  Horsepower is a factor of RPM, and at higher rpm, the
NA engines don't have a very high VE, so lose out on the power.


Perhaps most dynometers cannot measure
> the full torque of the diesel, because they do not put sufficent load on
> the engine, and are being biased by the huge rotating mass and slow
> combustion of the diesel engine.

 You can dyno anything. You get a result in foot pounds of torque. you can't
describe the volks diesel as huge rotating mass either. My 425 cummins,
yeah, sure, but not the little volks.
Remember horsepower is a function of RPM, so anything that revs slower, may
have lots of torque, but has lower horsepower due to the lower RPM's.
Horsepower is a dynamic thing, torque is more like a snapshot in time at a
given rpm, a function of cylinder pressure actually. Think of an itsy bitsy
F1 race engine delivering 1500hp at some unearthly rpm figure like 20000rpm.
It has such a high HP figure BECAUSE of the rpm.  Think in terms of there
being a series of torque producing events per revolution, and if you can
cram more of those into a minute, and measure them you get horsepower.
Measure ONE event, you are measuring torque. Design a cam profile and intake
system that can deliver constant flow through 15000rpm, you get a lot of
horsepower...

Anyway, other than cost I don't see any
> good reason to not get a turbocharged diesel. It doesn't seem to affect
> engine longevity with properly increased lubrication and cooling, the
> turbos last virtually forever because of low exhaust temperature,

No.  Exhaust temp is what you set it at with fueling and timing. It can be
really hot (1300F) or cold (600F) You have less chance of an exhaust
overtemp condition in an NA actually. Ther rest is very true.

 and
> they seem to get better fuel economy, especially under heavy load.

No.  They use more fuel.  Nothing is free- it takes fuel to make power,
higher VE allows more fuel to be injected, making more power.  Turbos only
make for a more efficient engine to allow getting more power from the same
package. Fuel economy is best in small NA engines, and now tdi's due to
electronics and direct injection. The TDi is a different cat... How to put
this clearly... The TDI engine has the ability to make more power, due to
factors effecting overall dynamic efficiency.  Therefore, it needs less fuel
to handle an identical load when compared to other engines. It has less to
do with the turbo and more to do with other tricks... swirl technology,
injection management, camshaft parameters etc...  But if you compare the
same engine, turbo, and non turbo, say, a 1.6 d vs td, the first statement
applies.  The turb engine will use more fuel.

Your
> chances of getting rear-ended by a fully loaded semi truck climbing a
> long grade are also greatly reduced ;)

That's the truth.  I used to drive an 82 Jetta d years ago.  50mpg, no
matter what I did.  It was great, until I got a TD Jetta. Never again man.
I get in an NA now, I feel like a target on the highway. I'd sooner drive a
40hp beetle... or a 1600 single port westy. Nobody expects those to move out
of the way...

Gee, I just proofread this, I come off as being so teachy.  Not meant to be,
sorry, but you said "please correct me if I am wrong".  Okay now write out
100 times, " I will not compare my diesel engine to a gas engine".....
:-))
-James
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