Do I need knock control?!?
Real Tuners episode 79 - Knock Discussion follow up.
Brian recently joined the guys from the Real Tuners podcast to discuss tuning, parts selection and how to decided what features you really need in your ECU and tuning equipment. (Go visit the Real Tuners Website and be sure to follow Real Tuners on Facebook)
The topic turned to knock detection and knock control on ECUs and (after a short rant from Scott) we came to the suggestion that ecu knock detection may not be as critical as it seems. This generated quite a few questions and concerns regarding how to actually tune ignition timing safely. The easy answer of course was "Know your setup, run the right fuel and just don't knock!" But what does that mean for the DIY home tuner and track guys? Are you destined to learn the hard way?
Check out the discussion and the follow up below! And check out our knock tools here while you determine what fits your needs.
(note - audio issue on the current recording misses initial discussion, but main knock discussion starts at rougly the 56 minute mark (though with small hiccup and skip on Scott's rant) and we revisit at 1:07:00 discussing tuning without knock detection)
Ignition timing (and preventing knock) are of course critical aspects of properly calibrating your engine, so why would we suggest that you don't need the feature?! Crazy talk? Just arrogant tuners that don't want to share their "secrets"?
We'll go back to the theme and phrase Brian used often during this discussion - this isn't a once size fits all industry. Deciding what features you need (and don't need) are often more complex than the tuning itself! Ignition is typically one of the most nerve-racking processes for new (and even experienced) tuners so the idea of using knock detection to save your engine should you push it to far is appealing. But it's useless if it's not properly calibrated and herein lies the problem.
As Brian's discusses Most systems require extensive setup specific to your engine to be truly accurate. This requires the use of a load bearing dyno and actually making the engine knock to calibrate the ECU. Don't get us wrong - when properly calibrated modern ECUs do an AMAZING job with knock control. And an an ideal world this would be perfectly setup on every car and ecu.
The truth it, tuning doesn't always deal with the perfect and ideal situation. For those street/strip tuner the truth is this feature just isn't going to be fully or properly utilized. There are some equations to calculate your centerline frequency and with some extra effort and care the filtering could be done (though this would be much more difficult without a dyno) but you are still introducing a non-negligible amount of uncertainty into you knock calibration. What's worse, you don't know if this uncertainty is erring on the side of caution or not! If you want to check out a live demo of setting up knock on a Haltech ECU take a look at their video.
So, what are our options? Just leave it safe, and hope that was safe enough (and if not learn through trial and error)?
Or, we revisit our toolbox and make sure it matches the garage we're working from and builds in our bay.
There are a handful of tools that can aid in knock detection from simple visual knock lights to audible knock detection systems found in dyno cells. You can check our line of Knock products here
To start, the first discussion should be what are your needs and tools available. As discussed, without access to a dyno properly calibrating a knock system for maximum accuracy could be difficult. So simply relying on an ECU with knock detection may not be the best primary tuning strategy. A main discussion should really be "what are the odds of my engine knocking?" Of course, that's the root of the issue - but not a complete mystery. Utilize your resources, research and understand what your combination is truly capable of, select your fuel properly, and decide how far you really need to push your engine. And remember, your engine may not be knock limited! This is of course easier with experience, and we often set our Turbo LS drift cars with a fairly safe margin on the ignition setting knowing we want a buffer and accepting the lower power output that comes along with this. There is always a risk in this assessment of course. Assumptions can be wrong, even from very experienced tuners. Issues arise in parts, fuel, conditions, etc. that can all change this safety margin you may have thought you had. This is part of tuning! There is always a risk and understanding these risks and how to mitigate them and solve them is as critical to entering the "correct" numbers in your table. Knock is scary, getting it wrong is scary - but take your time and understand what tools you have and how to review your physical and digital data as a whole system - then you can determine what tools fit your needs!
There are tools available that will work for the guys tuning off a dyno. Even for those guys that will be tuning on a dyno selecting an ecu based solely (or even largely factored) on knock detection may not always be the best decision and use of resources. Even with the best dyno and parts In some cases the ECU knock detection may not function with your setup. So let's discuss a few of the tools and methods available when knock detection is not capable with your ECU and engine combination.
Knock lights are just that - a light (or other visual indicator) that warn you when knock is detected. Sounds simple, and great - right? On the surface they are, but to understand why these may or may not be right for you let's understand first how they work.
A knock light works similar to the knock detection system on an ECU - it uses a knock sensor (typically a 2 wire Bosch flat response type) wired to a amplification and filtering circuit. The difference here comes in the filtering and speed. The Link KnockLink and most other knock lights use an automatic or simple filtering process that involves a learning process. The system will listen to standard engine noise with no knock present and set a base filter based on this noise and frequency range. As knock typically will be on a very different amplitude and frequency the system can now differentiate between standard engine noise and spikes such as those caused by knock. This makes these units very simple and easy to use and an attractive solution.
The drawback with these devices is again with the filtering and calibration. The filtering process makes a number of assumptions to determine what is and isn't knock. This can introduce a certain level of uncertainty and error especially when the calibration is done on inconsistent road surfaces and operating conditions. The filter is a one-size-fits-all application and typically cannot be tailored to your specific setup. In the case of extremely noisy systems the light may not work (as it cannot establish a narrow enough base filter) or cause inconsistent results and false or missed detection events. The circuits in these units are also not typically suited to analog outputs (and virtually never present) as the knock detection event occurs so fast the proper signal cannot be communicated to the ECU in most cases.
This leaves these primarily as a driver warning device. They are priced attractively starting at $200 and offer a certain peace of mind for drivers and street tuners. A knock light can give you enough warning and in most cases warn at the onset of knock giving a driver enough time to lift off the throttle and either sort out the issue on the track or make the tuning changes necessary. They are not fool proof and should be used along side other methods of verification. However for those that are tuning on the safe side and want a little peace of mind and warning a knock light is a great and affordable tool.
Knock Ears - Audible knock detection
There are also a number of tool available to audibly listen to engine noise and knock. The simplest of these is a mechanical Det Can and can be pieced together at your local hardware store. I will speak more to the electronic version here, but the idea is the same - a tool that allows you to listen to the engine noise via a set of headphones. Knock is very discernible from back ground noise and typically described as like "marbles in a coffee can". By skipping the filtering and letting your ears do the work you eliminates the drawback in setup and calibration of other systems. The Link KnockBlock is a popular and powerful knock detection system offered by Tuner Tools.
Most electronic systems will utilize an adjustable filter and gain to allow you to fine tune the audio output. There is still a very complex and chaotic system at work so understanding of what you are listening for is critical. In some cases (such as the Link KnockBlock) the unit may even include a canbus output that will allow it to integrate with your ECU or logging setup or log to their own software.
These systems tend to be significantly more expensive starting at $400-$500 and ranging to the thousands of dollars depending on features. Since this approach requires wearing headphones it's not always friendly to street tuning, and definitely not to track use. Audible systems work great for steady state and calibration processes but may not always work best in dynamic tuning as pinpointing the exact point of knock requires the tuner to mark the exact operating conditions when knock occurred. There are some more advanced system that integrate engine speed logging along side frequency analysis and knock logging - though this again requires some setup and understanding to ensure the data is useful. Some units such as Tuner Nerd offer audio logging that you can play back along side the digital logged parameters.
These are typically more suited for professional tuning and controlled calibration. The cost is not insignificant - though the gap is being closed and when used properly these can be a useful tool for the DIY tuner willing to put in the time, understanding and funds into properly learning and setting up the tool.
Using all your data!
In the end the best tool for preventing knock and properly tuning your ignition system is that squishy mass between your ears. Tools are only as good as the hand they are in. Truly understanding what knock is and why it occurs is more important than any knock detection tool or strategy. Think critically about what you are seeing. Higher IATs and higher cylinder pressure are going to be large contributors to the risk of knock. The risk increases more as octane decreases as well. During the podcast we discussed these topics -watching your IATs, picking the right fuel and taking a look at your data to make sure the engine is "happy". Understanding what you should and shouldn't see in your data along side inspection of physical parts and plug readings (and understanding the arguments behind reading plugs) can go a very long way into tuning for and preventing knock.
In many cases it's even possible to just tell when an engine is not happy and may be starting to knock. Engines should have a fairly smooth and recognizable tone and rate of acceleration during any given pull or run and most of us can tell when there is a small change or hiccup in the power band. This is often apparent in dyno curves or acceleration data as well. Knock by it's very nature is an inconsistent combustion event. A knocking cylinder will not generate and transfer torque as smoothly or evenly. Reviewing your acceleration data (engine or vehicle) and utilizing this along side you other data can be used to asses the possibility of knock. Factors such as engine RPM, drivetrain inertia and balance and even logging speed will all play a role in how reliable these methods are and should be used along side common sense and other data and tuning methods to achieve your end goal and engine longevity.
As always I have to stress that no tool in a band-aid for lack of understanding. Tuning is not a black art but it does require critical thinking, problem solving and a certain amount of patience. In the end our goal at Tuner Tools is to ensure you are getting the best overall package to suit your needs, skills, equipment and budget - while also ensuring what you need is capable within you budget. So what knock tuning method and tools are right will always come down to a personal case basis and all the information here should be considered with all the skepticism and questions you may have. As always if you have any questions on tools, equipment or even just tuning theory please contact us!
Any additional questions or topics you'd like to see me discuss? Let me know! I hope to be able to join the Real Tuners group on many more and look forward to the discussions with all of you!