One of PDXTuning's main goals is to post information that is beneficial to the community. In a passing conversation last year we spoke with TurboXS about some products that would benefit the community, a knock light is one of the ones we discussed. Recently as part of their DTEC fuel computer they released a knock light. PDXTuning immediately asked for the KnockLite as a stand alone product so we can help people in the community with other forms of EM understand the state of their tune.
The two most common forms of engine management for the Subaru's right now are reflashes and piggybacks. I will hold this discussion to the UTEC and to reflashes. Since PDXTuning tunes AP Protuner, EcuTek, and UTECs commonly it is easy for us to give detailed information about how they all work. Since the AP and EcuTek both rely on the stock ECU to run the car this discussion will treat them as equals.
What is a TurboXS KnockLite?
The TurboXS KnockLite is a simple stand alone unit that can be added to any electronic ignition car to monitor for detonation, and indicate a given RPM to shift. Since it has built in tach drivers it works on cars like the Legacy GT that do not have a engine speed signal to tap.
One of the most important aspects of a tune is the safety margin. If you push a setup to the point of regular detonation it will eventually fail. Detonation results in spikes of cylinder pressure that will either mechanically fail some engine component, or cause the motor to absorb additional heat that will melt the piston top. Keeping detonation at bay is absolutely essential, and ultimately it limits the amount of power a car will make on pump gas. This limitation is the reason why race fuel makes more power than pump gas. Race fuel has a greater resistance to detonation, which allows the tuner to achieve the optimum timing, fuel, and boost combination for your particular car's setup.
One benefit the UTEC has over reflashes is it notifies the operator when detonation is detected. Unfortunately the UTEC does not have a learning system like the reflash to deal with detonation. The UTEC relies on the tuner to set up the map so that it does not regularly detonate. It does react to detonation by pulling timing, just like a reflash, but it currently does not have the ability to adapt to a problem spot. In order to make up for this the UTEC notifies the operator by flashing the CEL after a detonation event is detected.
The stock ECU has a learning system in it, which over time adapts to the octane limitations of your car and fuel. While many people prefer the learning ability of the stock ECU, they are relying solely on the hardware to detect and adapt. While this is normally adequate, there are motors out there that fail due to detonation with reflashes so the system must not be perfect.
Each model ECU is different, so I will have to make some general statements next. The 02 WRX ECU was particularly bad about reacting to detonation at times. Subaru decided to stop listening for detonation after about 5700 rpm due to a limitation in the hardware. After the cutoff RPM the ECU would run the maximum allowed timing, without regard to occurrence of detonation. Provided the map was setup properly you could still tune safely. However in order to get the maximum out of the car on 93 octane you had to be absolutely sure that the car was never operated at it's maximum with lesser fuel in it. While it is easy to say you will never put in 89 or 87 octane fuel, there is nothing you can do about a gas station having old or otherwise bad fuel in their 93 tanks.
Subaru figured out the design flaw in that system and improved the system in future cars. Now the hardware is better so it is able to listen to higher RPMs, and after the point they choose to stop listening they do not add max timing. This has to have improved motor longevity, and allows the tuner to tune your car to a higher power level more confidently.
The question still remains, how often is my car knocking? One common statement made by car owners is I never hear detonation so it must not happen. We have come across people who should know what detonation sounds like, but are not hearing it. Part of the problem is detonation becomes damaging before it becomes audible. This means you may never be able to hear it while it is taking it's toll on your motor.
If you get in a bone stock car and romp on it you may well hear detonation. The problem is there are so many variables that contribute to lowering the detonation threshold. For example if you sit at a light for 45 seconds and then take off in a spirited manner your intercooler is not as cool as it was when the car was on the dyno, getting custom tuned. In this situation the map your tuner made may no longer be appropriate. 20-30 seconds later when the intercooler cools off everything is back to normal, but what happened as you rowed through the gears?
Everyone always wants to put a boost gauge in their car. Others ask what are the three most important gauges to add to the car. Typically the response is some combination of boost, EGT, oil temp, and oil pressure. If you think about it a knock detection system is as important as any one of those, if not more. None of the systems in there will kill a motor as fast as detonation. In fact one of the main reasons why you want to know what you are boosting at is to determine if you may be detonating. If you are boosting beyond the capability of the fuel you will detonate, if you are boosting beyond the level tuned for you may be detonating.
What about fuel and timing? They have as great of an effect on causing detonation as boost does. Rarely do people add wide band O2 sensors, and even fewer people monitor the timing they are running at any given moment. This is where a knock indication system is so valuable. If you rely on the engine management to do it's job you do not have to know what AFR, timing, or boost you are running. What may be more important that the exact AFR, boost, or timing you are running is if you are detonating. The TurboXS KnockLite is an inexpensive tool to help you understand more of what is going on in your motor. It is easy and clean to install, and perhaps best of all it only cost $129 MSRP.
Yes, it also is a shift light, so anyone out there wanting the extra little coolness of knowing when to shift you have that built right in. I can say personally that the shift light helps me out a lot, since I seem to have the habit of driving down the freeway in third gear cause I can not hear my motor with the stock CBE installed.