In all the posts i have read on this topic, no one has thought to question or discuss why these motors, or any motor provides more power and torque by tweaking the parameters of the timing and AFR's.
Its not rocket science, it does so because you are making the motor more efficient, ie; if the motor produces more torque at certain RPM's with the timing advanced then that is the ideal setting for the timing at that paticular RPM, with the fuel provided, if a motor produces more power at a certain RPM with a timing adjustment and then an AFR adjustment to correspond, then those adjustments are the ideal parameters to aim for.
If on the other hand by pushing the timing at one paticular RPM improves power output, but at another RPM decreases it,continual adjustments have to be made again to bring things back into line, and so it goes on, this is where the skills of the tuner come into play, modern ECU's have much more indepth posibilities to fine tune all the necessary adjustments needed to maintain maximum performance with the fuel available at all times, our 25 year old cars have a somewhat more basic control module, but it still has the capability to be fine tuned.
So my final question is, if by fine tunning these motors we are in fact making them more efficient, why is this going to put the motor under more stress than it was designed for ?
Surely by running it less efficiently, it is going to stress things more in the long run as for one, your wasting the potential of the fuel's calorific value by not extracting its full potential, so you end up running it richer, to keep it cool, and causing premature wear in the process.
As i see it, If you over advance an engine it will give you less power, it wont keep giving you more power untill it destroys itself, detonation sets in because the timing and AFR's are wrong, and this would show up on a dyno as less power, who in their right mind would tune a car untill it did this ?
Just my ramblings.:)

Anthony.

Ant7, the reason you get more power from more advanced spark is that, if you look at a crank angle vs. cylinder pressure graph (this post has one midway through: http://www.evans-tuning.com/forums/viewtopic.php?f=3&t=136&hilit=combustion%252C+igni tion+timing ... looks like a lot of info from "The Internal Combustion Engine in Theory & Practice", which I have a copy of ... someplace ...), you get a higher (and earlier starting) combustion pressure. The increased area in the diagram, which is basically your power gain, is all on the left side of the curve. Once combustion is complete, the expansion side of the curve looks pretty much the same. So the loads on the pistons, rings, & bearings do go up, and they go up much faster than the output torque of the engine. This may or may not be an issue depending on engine design (probably not with the metzger engines - the bottom end appears rather stout).

There were a couple of references to knock monitors in this thread (thanks to the posters!) - I will probably get myself one sooner or later, and once its operational, I might add a chip & see. Without knock control, I am too nervous getting rid of the cushion the factory installed.

And while there clearly is room for improvement, you do have to give Porsche credit - the power to displacement ratio for their engines was pretty darn good for their time, especially considering their longevity.

I have spent a lot of time at the dyno over the years. My experience has been that timing, while important, is secondary to AFR in terms of importance - as it relates to both engine performance and engine life.

It has been my experience that once a base timing curve has been established, tuning for AFR will invariably yield the best results - i.e. the smoothest, most linear curves. I have actually found this to be most visible when tuning carbureted engines with radical camshafts where the base jetting produced peaks and valleys along the power curve and how AFR adjustments - through the use of different emulsion tubes, main jets and air correctors - smoothed out those peaks and valleys resulting in a more shapely/linear power curve and (duh) more horsepower.

Now, I would like to note that some engines preferred 12:1 AFR and others preferred 13:1 - as evidenced by their sound, behavior, and power output - but none of them seem to enjoy 10:1. :)

All that said, however, it would be narrow-minded to think that any ONE thing is the "secret" to engine performance. Tuning engines is a balancing act...an exercise in compromise - all the changes directly affect one another and you have to look at big picture. Is timing important? Of course! Is it more important than AFR? I don't think so; and vice versa. Tuning engines for peak power tends to lead to disaster - i.e. short term gains at the expense of engine life. We try to tune for a power curve that - based on a great many variable criteria - will net the best results in terms of drivability and purpose.

Never lose sight of the big picture...

^ Well said. Optimum AFRs and max power with minimum timing, it sounds so easy to write it like that. But it is true.

ok, what about Atkinson cycle...

Just because it is in a graphic doesn't mean it is correct.....as Steve Wong's dyno sheets prove.

Scott

^^+1..

Hi Burgermeister,
Thanks for that, however, i am well aware of the basic function of the internal combustion process!:)
Sorry if a gave the wrong impresion with that last post, but that was not the point i was trying to get across.
I also take your point on a longer burn process having a higher risk factor on the pistons and rings etc, however, i was of the understanding that these engines were designed to maximise the full potential of the fuel that was available, So,,, by fine tuning the ECU parametrs ie; timing and AFR, all your doing is making more use of what is potentialy already there.
If on the other hand you are tuning for power that was way off from what the original desgn capability was' then thats a diffrent matter.

Anthony.

http://forums.pelicanparts.com/uploa...1340297503.gif

Thanks Hydrocket, as that further exemplifies the insignificance of tweaking the
AFRs when they're close to the ideal (12.6), as is the case for a stock 911 engine.

Loren,

It's a bogus chart. It's something someone like you probably came up with. All one has to do is look at real dyno results to see that chart is just plain wrong.

Scott

I've been away from here for about 3 years now, since keeping my business open through the recession took precedence over tinkering on my Porsche. Things are better now and I have got back to work on my car. Came back to the forum today and Loren is still grinding his axe with performance chips. Glad to know some things never change...

http://forums.pelicanparts.com/uploa...1340304666.jpg

"It has been my experience that once a base timing curve has been established, tuning for AFR will invariably yield the best results - i.e. the smoothest, most linear curves. I have actually found this to be most visible when tuning carbureted engines"

- Mr9146 (Marco - TLG Porsche) -

Maybe Marco can explain how it's possible to 'tune' a carb'ed engine (much less a CIS
or mechanical FI engine), i.e. tweak the torque over the RPM range with various loads
by varying the AFRs within a few points of whatever ideal AFR is desired, AND yield significant
torque/performance gains.

"It's a bogus chart. It's something someone like you probably came up with."

Sure, as it's in all the engine books, e.g. Bosch, "Combined Ignition and Fuel-Injection System
with Lambda Closed-Loop Control", pg 4, ISBN 1-85-226009-2, 1985.

Loren loves the books and charts and theories, you should come join us out here in the real wold .

Well, Bosch, et al, should be ashamed.....

Why? Because Peak power is not made at 12.6:1 on any engine I have seen on a dyno and I suspect most engines would have real problems if tuned to 15.4:1.

Scott

The Q should be; What engine does that chart correspond to?

That is, mixing dynamics influences the chemical kinetics . . which influences what delivery ratio works best for peak power or economy.

So, Loren is a troll for posting that unassigned graphic

winders is an idiot for saying "bogus."

And I'm an idiot for responding. http://forums.pelicanparts.com/suppo...s/a_frusty.gif

It is truly sad to see an obviously passionate person so engaged in activity that results into a net zero at best if not a negative in terms of adding value.

Brain chemistry is a strange and wonderful thing that causes people to respond in this way. That is the only thing I can chalk it up to, it clearly isn't rationally driven. Sure isn't motivated by economics, as has been stated in most threads this does nothing to build trust or patronage for services and products.

Can you imagine what would happen if you were engaged from a business perspective and had a difference of opinion!

Good luck

Just for clarity Loren didn't post it first. And I'm an idiot for pointing that out. ;)

Who said he did post it first??

Scott

That was my interpretation of post 196. Am I wrong?