[petevb]

I'll weigh in and give my opinion: There is certainly truth to some of what Loren says, but he also makes some big errors and reaches invalid conclusions because of them.

Taking his three main points out of order:

Point 1:

Originally Posted by Lorenfb

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

Clearly false, as others have said. Yes there is an area around ideal where there are limited gains, but Loren clearly doesn't understand how small that area is. If by "within 2 points" he means either a 10.6 AFR engine, which is terribly rich, or 14.6, that's a dangerously lean place to try to make max power. There is without question a significant, measurable direct effect on hp across this range.

Even more important, however, is the indirect effect the graphs do not show:

The first of these is the interaction between AFR and timing- the leaner tune is much more likely to detonate, and timing must be adjusted accordingly to maintain a given margin of safety, while it must be adjusted in the opposite direction for the richer motor. In fact across the range air fuel ratio, timing and safety margin are linked. So while a graph might show a relatively minimal drop in power with a 13.5:1 ratio, what it doesn't show is that timing must also be pulled out to safely run that ratio with the same safety margin, compounding the effect.

A second indirect effect is on engine temperature. A richer engine runs cooler which is why much good tuning is done with exhaust gas temperature measurement, but too rich and you get issues with cylinder wash-down, etc, that negatively effects reliability. As tuning for "Performance" naturally includes durability and reliability, these issues can't be ignored.

Taken together all of these require a well tuned engine to run in a relatively narrow A/F ratio band for peak performance. The ideal A/F ratio varies not only from motor to motor, but also within one motor: gas quality and particular point in the rev range (volumetric efficiency) both have an effect.

Now a separate issue, to some extent, is did Porsche get the air fuel to be ideal in the first place? If it's already ideal then obviously that can't be improved on. As stated, however, Porsche engineered a generic solution for a range of fuels and usages. When a given gas quality, maintenance standard, intended usage, expected conditions, etc are known I do believe it is possible to optimize the A/F ratios for that, improving (slightly) on Porsche's necessarily generic solution.

Point 2:

Originally Posted by Lorenfb

performance tuning... compromises the margin of engine safety that Porsche included

This I generally agree with. There is no free lunch, and the ability to run well on all the fuels and engine conditions Porsche engineered for is almost certainly reduced if a tuner successfully produces more power. Remember they only have two main knobs to turn- fuel and spark, and one can't perform magic with these two knobs.

However. As others have pointed out, what's an "acceptable" margin of safety is a non-trivial question. We've seen Porsche themselves change their mind on this question by tuning different model years differently.

My other car, a BMW 1M, offers a more dramatic example. It uses the same N54 motor with very minor tweaks as was launched in 2006. Then rated a 300 hp and 295 ft lbs, BMW has since decided that more is perfectly safe, and with software changes my version of the same motor is now rated at 335 hp and 370 ft lbs (and in reality often delivers those numbers at the wheels on a dynojet, suggesting it's making closer to 370/ 410). Not coincidentally my motor's ratings are near identical to what some chip tuners have been providing for the older version of the motor for years. Was the margin of safety compromised? Absolutely. In an acceptable way? BMW thinks so.

Point 3:

Originally Posted by Lorenfb

the reality is that performance tuning is neither an effort requiring any knowledge and capabilities beyond what most back yard mechanics know... This 'tuning' is nothing more than a minor engine tweak... Additionally, this effort hardly requires any real knowledge...

Yes it is true that DME tuning is now becoming more accessible to the masses. You can go out and use laptop to do it yourself if you're willing to go to the effort, and I've done that. And making more power is not a mystery- as we said there are only two knobs. So what's the difficult part?

Knowing where the line is.

Knowing how far you can push the motor while preserving the needed margin of safety is the difficult part, and that's where a good tuner earns his money. It takes real testing, ideally on both the road and a dyno (preferably load dyno, engine dyno being best), looking at EGTs, etc. And it takes knowledge.

A tuner is playing a high stakes game- on the one hand there is the desire to maximize power, but on the other they can't blow a customer's motor up. It's a small community, and that's the kiss of death, weather you're tuning for the Daytona 24 or street car enthusiasts. A tuner's livelyhood lives and dies by reputation, and blowing a motor is the surest way to lose it.

So sure you can tune your car yourself, crank some timing and make more power, but without the knowledge of where the line is you're playing Russian roulette. A good tuner, on the other hand, is playing chess, and a good one has played the game many times before. Unless you really know what you're doing I'd strongly suggest you don't go off turning dials and leave it to someone who does (and has more to loose than you do, if they are good). There is also some trick, however, to knowing who a good tuner is, as there are also bad ones.

I do believe Loren is not being straight about the dyno chart he posted, making me question not only his points but his ethics and motives.