Forum » General Tuning Discussion » Filtered Knock Audio - What's my options?

Filtered Knock Audio - What's my options?

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Incoming wall of text.

I've spent the last week tuning a 1.5JZ engine that I've built for testing purposes in order to expand my tuning horizons and so far everything has been going to plan. The engine is using pretty much refreshed stock internals, running slightly higher compression than a normal 2JZGTE (8:5:1), with a small single turbo and a mostly stock fuel system with uprated pump to support 400-450 ish horsepower/torque at the flywheel. It's got every sensor that I could get on it without breaking the bank (oil pres, oil temp, fuel pres, bosch knock sensors, egt sensor etc)

With the current level of tune, the engine is producing a healthy amount of power & torque @ 1 bar of boost(370 hp/ 390 ft/lbs @ wheels) and I could just leave it as is and it would be an acceptable tune for your average daily driven tune/weekend toy etc. However in my search of furthering my skills, I really want to push the setup to a level that I can confidently say it the limit of this fuel, before backing down.

I'm sure part of this is down to my level of experience, but when trying to optimize the ignition tables under peak torque and high rpm areas on 98 octane (UK) pump fuel I'm starting to get a bit nervous trying to dial in the ignition with no knock.

The engine is run on a Link Storm, and has two bosch knock sensor (0261231006) wired up in place of the stock 2JZ sensors, mounted in the factory locations.

I'm also running a Phormula Knock Analyser Pro, which also uses the same bosch knock sensor as mentioned above, which is mounted in between cylinder 5 & 6, directly on the block just below the deck. This knock monitor is just giving me a way to listen to the raw output of the knock sensor, and from what I can tell there seems to be no audio filtering present, and there is no way to filter it according to what type of engine bore size I'm listening to.

Now when it comes to low rpm ignition tuning, using steady state and live torque readouts everything has been fine. Inducing low level knock to form the basis for my knock threshold on the link's onboard knock control, I've been able to hear the knock on the headphones and have seen this knock signal be produced on my Link logs at the same time/rpm etc. And calibration of these areas has been quite straightforward, and if I induce knock then the Link captures it and pulls timing as expected.

However once I start pushing to 4500rpm or higher on ramp runs, the audio I'm getting through the headphones gets really intense with the sound of the valvetrain/pistons/boost etc. It's getting to the point where I'm finding it hard to trust what I'm hearing as there is just so much going on, and unless I got a really large knock, I wouldn't be surprised if I missed low level knocks.

So currently I'm just monitoring the patterns of whats being produced on my ECU logs, whilst trying to make my knock threshold levels more strict to the signal patterns with each run. All whilst trying my best to hear beyond the noise for anything on the headphones.

Given that a big knock under full boost and high rpm could end in tears, I don't really fancy just winging it and slamming in some high ignition numbers and hoping for the best and tuning from there, even with this being a test engine. Surely there is a more level headed way of tuning these areas to their optimum. Maybe I'm just being a bit anal/unrealistic, but I'd like to reach the point where what I'm hearing is almost perfectly reflecting in my ECU knock logs regardless of what RPM/load I'm under.

Just having a quick browse through the forum and google search, it seems like Plex Knock V2 is the device to have for in ear audio that can have a filter applied to it, among some of the other useful features it can provide.

Is the plex still the one to have, or are there any cheaper alternatives which can provide audio output frequency filters?

Are there any tips/tricks anyone has got to approach this higher rpm ignition tuning that I can give a go in the meantime?



I'm not familiar with the Phormula knock monitor sorry. The Plex definitely allows the audio to be filtered which is useful on some engines but I find it's still essential to try the various options to find which works best for your application/engine. If you can clearly hear knock at low rpm though you can use the phormula along with the link closed loop knock control. Once you have the link knock control accurately detecting the knock that you can hear at low rpm you can then trust the system is working as expected. At higher rpm you should expect to see quite large spikes above the threshold if knock occurs, not small increases that are hard to discern.

The other product i use regularly is the Link G4+ Knock Block however this uses a simple wideband filter for the audio and isn't adjustable.

Hi Andre,

Thanks for the response.

Got another 2JZ in the shop at the moment that has been tuned previously by someone else, but the knock features hadn't been setup on the Link ECU so the customer wanted it implemented for safety. Whilst checking it over I thought I'd take your advice into account whilst putting some form of knock control on it.

Again, setting the knock levels/threshold whilst doing low load knock down at low RPM's is giving me good repeatable results that I can verify over audio. But once going to high RPM I'm still a bit hesitant about the results.

So in the first attached photo, is basically what I'm seeing on pretty much every ramp run after 4k rpm. Some increase in noise every now and then, with one cylinder maybe reporting twice as much noise as another (140 vs 340) for a very quick period before returning back to the average noise level seen on all other cylinders. Is this the typical noise behavior you would associate with your description of "not small increases that are hard to discern."

The second photo is actually of the engine hitting the rpm limit, using the default link ECU ign cut settings. The loud bang from the ignition cut is being picked up by one of the knock sensors. This obviously isn't the same as the engine knocking its tits off, but presumably this sort of spike is what could be expected from a large knock spike in the higher rpm's correct?


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