Most are under the impression that the so-called 'performance' tuning of a stock
engine is an effort that is specialized requiring knowledge beyond simple
automotive engine basics, and that the effort maximizes performance
beyond what Porsche was capable of achieving when they developed their
engines without any compromises or trade-offs. So what is 'performance'
tuning for a stock unmodified engine really?
Well, the reality is that performance tuning is neither an effort requiring any
knowledge and capabilities beyond what most back yard mechanics knew
when the internal combustion engine was first developed nor yields any
additional performance without engine compromises and trade-offs. The simple
fact is that performance tuning is nothing more than increasing the timing
advance beyond what was specified for reliability by Porsche. Furthermore,
the hyperbole of tweaking the AFRs for added performance yields basically
no performance improvement once the AFRs are within one to two points
of the ideal AFR of 12.6, which is the case for a factory stock engine.
Thus, it's mis-leading to most to indicate that tweaking the AFRs will improve
performance for a stock engine.
Dyno tests (see below) have demonstrated on a 911 3.2 engine, whether
stock or non-stock, that for every one degree change in the advance timing,
a three to four horsepower change occurs from about 4500 to 5500 RPMs.
Many 911SC engine builders were aware of this effect and achieved a simple
performance effect by just loosening the distributor and slightly readjusting
the timing a few more degrees advanced, as has been the case for many
years with all early non-ECM (engine control module) controlled Porsche engines.
Obviously, this effect is limited to small changes in the timing.
So based on this simple and basic effect, it can appear to a Porsche owner that
so-called performance tuning has really accomplished something significant when
in reality it has just compromised the margin of engine safety that Porsche included,
to just achieve a marginal performance change. This 'tuning' is nothing more than
a minor engine tweak requiring no real testing and evaluation, as would be the
case for a major engine development effort. Additionally, this effort hardly requires
any real knowledge other than being able to buy a laptop, a 'tuning' app, and
programming a memory chip, i.e. An effort now days learned in high school auto shop.
Like many of the automotive performance products, 'performance' tuning is just
another marketing game of convincing the car owner that the owner needs
the product and relies heavy on word-of-mouth evangelists to promote the product
image. As is usually the case with hyped products, few purchasers really understand
what the product really is, what it really does, and what real effects it has.
So included in this thread are graphical data from dyno runs which demonstrate
what the so-called performance tuning really is all about and the myth that exists.
For more testing data on this topic, read here:
Tests
Bottom line: Therefore in summary, the dyno tests demonstrated that small changes in ignition
timing result in significant torque changes versus small changes in the AFRs which produce very
little effect on torque once the AFR is near the idea. Besides, the AFRs are changed continuously
based on the intake air temp, irrespective of what the 'tuning' setting was. Based on this,
'performance' tuning of a stock engine in reality is basically just 'pushing' the ignition timing,
given the marginal effect of an AFR change, beyond the stock values and nothing more for the
claimed performance improvement. These were the actual results obtained for a 911 3.2 engine
during a 'live' dyno session. If one disagrees with the results, then one can always buy dyno
time and demonstrate a different outcome.
Here's the dyno graph where small changes (3-4 degrees) in the timing resulted
in significant torque changes:
Here's the dyno graph where changes in the AFR had basically no effect on torque
once the AFR was close to the ideal of 12.6:
Here's the well known standard graph of how ineffective AFR changes are on
torque once the AFR is near the ideal of 12.6 (AFR = Lambda X 14.7):
Graphs
Additional Supporting Data:
The actual torque changes are only about 3% over the AFR range of about 11.8 to 14.7.
Reference:
"Automotive Handbook - Second Addition", Bosch, 1986, pg 439, ISBN 0-89883-518-C
"In the areas of interest - near the maximum power point and the minimum fuel
consumption point - those curves are relatively flat. Even if the system can be
adjusted to deliver the perfect mixture (just at the point of maximum power),
the gain promises to be pretty small. There are no huge amounts of horsepower
to be unlocked there."
"Bosch Fuel Injection & Engine Management", Charles O. Probst, Chapter 7, pg 7,
ISBN D-8376-0300-5