TECHNICAL ARTICLES
Volumetric Effeciency (VE) - This is a term that measure how effeciently your motor injest air through the intake
and expells the exhaust gases out the exhaust side. I put this first for a reason. This is a very important term
to understand, because most engine modifications effectively change the VE of your motor, and hince why you
decreases or increases in torque and power at various rpms. Mathimatically, VE is the percentage of air that the
motor injests and expells vs the total volume of air the motor could potentially injest and expell. First the easy
part. How much can your motor injest. Lets use the 2.0L FS motor as an example. Its total displacement is 2.0L's,
and it has four cylinders, so each cylinder displaces approximately 0.5L's. Now if the motor were 100% effecient
at all rpms it would injest 0.5L's of fresh air each cycle then expell it. Unfortunately, a 100% effecient motor
is impossible. How effecient your motor actually is unknown, but as a general rule of thumb most dual overhead
cam engines have maximum VE's around 85-90%. This actual numbers are not important though. What is important is
the VE curve, or a chart of VE vs RPM. You VE curve will have the same trend as your torque curve, as measured
on an engine dyno or a wheel dyno. So your peak VE will occur at peak torque. Without changing the displacement
of the motor you cannot injest any more air, but you can change the VE of the existing motor. This takes on
infinate degrees of modifications, from something as simply as changing the air filter or as complex as reworking
the cylinder head with larger valves and ported runners. So we want to change the VE of the motor? Almost all
performance modicafications will increase high rpm VE while sacrificing some low rpm VE. Recalling earlier
statements, this means that the high rpm torque will increase and low rpm torque will decrease, and where torque
increase, so does power. Learn this and understand it, as you will hear this again and again.
Dyno - This is a term that generally refers to automotive dynamometer, but could also refer to an engine
dynamometer. A dynamometer is a piece of equipment that is used to measure the power and torque output at the
wheel of a car or crankshaft of the motor for an engine dynamometer. Most automotive tuners use an automotive
dynamometer, which I will refer to from here on out. Dynos come in a variety of shapes and sizes, but the most
popular dyno, is the Dynojet dynamometer. The Dynojet utilizes large drums of known inertia, mass, and
circumference. Your car is straped down so that your drive wheels rotate the drums. Based on how fast and how
quickly the drums are spun, a computer can calculate the power and torque that your car is creating. The dyno is
one of the best tuning tools out there, and is the only way to quantify the actual gains of a particular
performance modification. Keep in mind that a dyno measures power and torque at the wheels. This is what is
truely important to you anyway, as this is the power and torque that drives your car, but note that between the
crankshaft and wheels are the transmission and drive train. Each of these components introduces losses in output
due to friction and inertia, so there is typically a 15% loss (for a manual transmission) in torque and power
between the crank and the wheels. Automatic transmissions or AWD drive trains incurr greater losses. The costs
of running your car on a dyno are not cheap though. A typically session of 2-4 runs, way cost you $75-$100, or
shops will rent the dyno for $100-$200 per hour.
Tuning - Tuning is a process of altering fuel delievery and ignition timing to optimize performance for a
given car, whether it be to achieve maximum horsepower or maximum fuel economy. Tuning is a very generic term
that is often used without any understanding as to what it truely means. This confusion can probably stem from
the fact that there are many ways to tune a car, and the methods for tuning will depend on the car itself. For
instance, a carburated small block Chevy can be tuned with a handfull of springs and a phillips screwdriver for
altering carburator calibration and distributor timing calibration, where as a modern fuel injected car would
require that the ECU be reprogramed, unless additional electronics are used.
The degree of tuning necessary for a given car depends on the degree of alteration to the car. A stock car or
a car with your basic bolt-on modifications will not need to be tuned to run properly, but as the degree of
modifications increases, tuning begins to become a necessity. Just about all stock production cars are tuned for
reliability, reduced emmissions and fuel economy, leaving room for small improvement on even a stock car for
increasing power. Primarily tuning comes into play when the motor has been radically altered. Modifications that
will generally necessitate a tuning are cam changes, cylinder head modifications, bottom-end changes, and force
induction. With a highly modified motor, significant gains can be seen from properly tuning the motor.
In this day and age of fuel injection, there are alot of options that will allow an enthusiast to tune his car:
1) ECU Reprogram - You can have the ECU reprogrammed. This is a process of altering the fuel and ignition timing
maps that are stored in the "brain" of the car. Unfortunately will most likely require shipping your ECU off to
someone else. In order for the to properly tune it to your set up and modification, you need to provide them with
as much information as possible. The best data to provide is air-to-fuel ratio data throughout the entire rpm range.
This may be an iterative process too, in which you have to send the ECU off a second time for some fine tuning.
2) Piggy-back Electronics - These electronic devices take on many shapes, sizes and colors, but the basic principle
is the same. These devices intercept one or more sensors on your car and alter the signal to give false readings
to the ECU of the car. The ECU will in turn alter the fuel delievery and ignition timing based on the altered signal.
This is a very effective method for moderate levels of tuning and this gives the user control of the tuning as well.
This is a very attractive option for people on a tight budget and are not running a radical motor.
3) Stand-alone ECU's - These electronics devices also take on my shapes, sizes and colors, giving the customer alot
of options to choose from. Basically a stand alone ECU replaces the job of your stock ECU in controlling the motor.
This is the ultimate solution as it gives the user full control over the motor, so it can be tuned for any possible
configuration. The downside as the cost of these "big-boy toys" can easily cost over a $1000 to as much as $5000 for
parts alone. Installation is often tedious and requires a working knowledge of modern cars or be prepared to shell
out at hundreds of dollars for installation.
|
|
 |
