Newsletter 33

09 May 2006

 

Welcome back

 

Before you begin filing this for further reference, please do check out my massive new K&N stock.

I am sure you will find something for your Car, Boat, Plane, Pickup, Motorbike, ATV…

And the prices have decreased in most instances, too !

 

Recently my long-term insurance broker confided in me that there was a cheaper product on the market, than he originally sold me.

He apologised by mentioning “It was not available at that time”.

No need to apologise. The world turns a little every millisecond.

Often people forget that we also upgrade. Just because it was not available last week, does not mean it is not on the shelf right now.

 

A few years ago, I was convinced that Knock detection equipment, which could be swapped from vehicle to vehicle for diagnostic/tuning purposes was impossible to mass-produce. Nowadays you even get Individual Cylinder Knock control that is a permanent installation. But it will cost a few grand.

 

Before you ask, “what is knock?”.

Any rude sound (never mind how soft) emanating from your combustion chamber, spells trouble.

Normally immediate and big enough to put a stop to your trip.

The following article I pulled of the Internet, explains it best:

Background

Engine Knock-that annoying rattling sound that sometimes comes from under the hood of your pride and joy, is a killer. We have all heard the stories of blown head gaskets and broken pistons. Maybe it has already happened to you, too. But just what is knock, sometimes also referred to as detonation?

The knocking sounds you hear are the cylinder walls set into oscillation by intense pressure waves, caused by abnormal combustion. Normal combustion is a controlled burn that starts from the spark plug and spreads outward, causing a pressure rise in the combustion chamber. This pressure is then converted into torque on the crankshaft. Ideally, the peak pressures will occur about ten to fifteen degrees after top dead center (TDC), as the piston is on its way down.

Detonation is a form of abnormal combustion that starts off right, but at the last millisecond, something goes wrong. The remaining air-fuel mixture, called the "end gas", explodes all at once, instead of burning in a controlled way. Resultant engine damage is caused by an instantaneous pressure rise that can excede 1500 psi. This is more than double the normal peak combustion pressure, and will blow head gaskets, break piston ring lands and hammer the rod bearings. Another form of damage seen is that the tops of the pistons will be eroded and can even melt.

High octane fuels are resistant to detonation because they contain compounds that slow down the chemical chain reaction we call combustion. If left unchecked, these chain reactions would quickly escalate, resulting in increasing damage to the piston and other engine components. All fuels, regardless of octane, have a knock limit. This is reached when the temperature of the "end gas" reaches an autoignition point. Combustion chamber designers use high swirl inlets and large "quench areas" to fight this "autoignition" problem. There are other factors beyond these mechanical design features which influence "end gas" temperatures. Some of these are: (1) Intake charge temperature, (2) Coolant temperature, (3) Compression Ratio, (4) Boost pressure, (5) Spark timing, (6) Air-fuel ratio, and (6) Humidity.

An increase in compression ratio, boost pressure, or spark timing will increase peak cylinder pressure, which in turn raises the "end gas" temperature. Higher inlet and coolant temperatures also increase the "end gas" temperature. Richer mixtures can be used to cool the charge. At some point beyond about 10:1, however, will again increase the tendency to detonate. A decrease in humidity will also tend to increase detonation.

Solutions

Some things you can change, and some you are stuck with. Obvious things to do are get cold, fresh air to your air cleaner, use the best form of charge cooling (intercoolers) you can afford, and work on your cooling system to bring the temperatures down. Get an Air-fuel meter (O2 meter), and if necessary, install a fuel enrichment device. For turbo/supercharged engines water-alcohol injection can be very effective, but the volumes required mean constant refilling and maintenance, so in the long term it is a specialized solution that has a lot of drawbacks.

Spark retard, within limits is the most powerful means of controlling detonation. Traditionally, this has been a manual affair by simply cranking the distributor back "x" degrees, Some electronic devices can retard timing in relation to manifold or boost pressure and other devices offer simple manual knobs you can alter the timing with if an audible "ping" is heard. Many newer cars are quipped with knock sensors that retard the timing when detonation occurs. This form of closed loop spark control where the vehicle's ecu automatically retards all cylinders when detonation occurs, a situation we call "retard all". On a select few modern engine controllers (Porsche, Corvette) the microprocessor is programmed to retard individual cylinders as knock or detonation occurs. The problem with either of these approaches is twofold: First, the OEM carefully maps a complex set of spark curves and only allows a small degree of retard to take place, typically 4 degrees; Secondly, these ecus are highly specific and are not readily adaptable or programmable for other applications.

It is not a simple matter of hanging a microphone on the engine and listening for the tell-tale "knock". If you have discussions with OEM powertrain engineers they can tell you of the difficulties they face in the areas of signal discrimination or "noise" as well as the issues related to how the actual control over the timing should be done.

Preignition and detonation are two separate and distinct events. It was first pointed out as far back as 1906 that the two phenomena were not only quite distinct but were in fact not related to each other. In the first place, preignition in itself does not produce an audible "knock" and if it is audible at all it could be described as a "dull thud". Because preignition is frequently brought about as a result of persistent detonation, the distinct "knock or ping" of the latter came quite erroneously to be associated with it.

It is by no means uncommon for preignition, or in this case it would be more correct to describe it as autoignition, to occur at the same phase as the timed spark. In this case the ignition can be switched off, and the engine could continue to run perfectly steadily without the slightest observable change in performance, sound, or any other characteristic. The danger, however, lies in the fact that all control of timing can be lost and ignition may creep in earlier in the cycle.

The danger of preignition lies not so much in the development of high pressures but rather in the very great increase in heat flow to the piston and cylinder walls when the ignition occurs too early in the cycle. This increase in heat flow, in turn, raises still further the temperature of the hot spot or surface which is causing the preignition resulting in even earlier ignition. At some point the temperatures are elevated to the point where the incoming charge is ignited, causing backfiring in the inlet tract. The belief, still widely held, that preignition can give rise to dangerously high cylinder pressures is totally false. Under no circumstances is the peak pressure resulting from preignition appreciably higher than from a spark-initiated ignition and, in both cases, the peak is reached when the maximum pressure is attained at or just after top dead center, that is to say, about 10 degrees earlier than the normal optimum. As the time of ignition is further advanced by either advancing the time of the spark or by earlier preignition, the maximum cylinder pressure falls again due to the excessive heat loss, for the piston is then compressing gas at or about its maximum temperature, and the intensity of heat flow is increased many times. The danger lies not in the production of excessive pressures but of excessive heat fow. The intense heat flow in the affected cylinder can result in piston seizure followed by the breaking-up of the piston with catastrophic results to the whole engine.

In nine cases out of ten, preignition is initiated by overheating of the sparkplug electrodes or some sharp point or edge that has gone "critical". We are accustomed these days to focus all our attention on the subject of detonation for it is the limiting factor controlling the performance of a spark-ignition engine. We are apt to forget that the real danger is that it leads on to preignition. In itself, detonation is not dangerous... It is the preignition it gives rise to that can so easily wreck an engine.

So after reading this and then asking how difficult is it to overhear your engine detonating away, I searched for a sound clip:

This log show second and third gear. If you play this sound file, which corresponds to this log, you can hear the same sounds that the ECU hears.  The pinging is audible just after the shift to third.  It has a fairly distinctive sound, that I would describe as similar to the "twang" that you can get from flexing a piece of sheet metal.  You will also notice a rather loud crackle around the top of second.  I hear this a lot, and I am fairly sure that it is electrical interference, rather than a mechanical sound from the engine.  I can't be certain that the ECU is actually hearing this at all... it could just be due to how I have my recorder wired.  You will notice that it does NOT show up as knock, even though it is quite loud.

Maybe now you know how bushed I feel after Dynotuning a car for a few hours. Constantly listening for that telltale sound telling me something is horribly wrong.

Doing a few cars in a row like these Nissan V6’s helps, as their engine sounds are similar.

 

 

 

 

 

 

 

 

I think people in Namibia are far too reluctant to praise a good service or product.

Maybe that is the cause of the lack off Service in Namibia ?

If nobody cares, why should anybody perform…

So imagine how I am going to treat this customer the next time he comes into my shop; ”Just a report back to you concerning my Cruiser that you have tuned. Toe ek Windhoek toe gery het oor die Bosua pas het ek so 5.2 km/l gekry. Donderdag het ek toe oor Spreetshoogte teruggekom (500km) en 6.7km/l gekry. Dis een moerse verbetering.

 

Wat nog beter is is dat ek amper nooit hoef terug te change van 5de rat nie - ongelooflik. Sal hom nou graag op die teerpad wil toets sometime. Anyway, nogmaals baie, baie dankie vir die dynatune en al die moeite - dit word baie waardeer.” Like Royalty, that’s how !

 

Wishing you a pleasant 2 weeks work before it is Holiday time again

 

Nick