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Engine Knock Detection – Plex vs Phormula vs MoviChip vs TunerNerd

Engine Knock Detection System Shootout - Collage of products

A comparison of some of the main engine knock detection systems available for the automotive aftermarket including Plex Tuning, Phormula, MoviChip & Tuner Nerd. I list the features I think are important and score each product for each feature to come out with a winner.

NOTE: This is not a test of the performance of the products. It is only a comparison of their feature list.

First I will detail the products in the test, then the important features, then a table scoring each of the products according to these features, concluding with an analysis of the scores.


The Engine Knock Detection Products

The products in the test include the Plex Knock Monitor V3, the Phormula KS-4, the MoviChip KSC2 and the TunerNerd Knock Monitor Pro Elite.


What Features Are Important & Why?

Some things I want, others I don’t

I don’t care about

The feature I am not interested in is audio. I believe audible knock can be detected with the ear with a normal lap top (connected to an engine bay mounted microphone or tapped directly into the knock sensor) and free software (APO Equalizer & VLC Media Player). In short, I personally do not see the need to pay for an external device to listen to engine knock.

I do care about

The features listed below. Some of the features are a nice-to-have, others I deem as essential.

Engine load input – Nice to have

It’s essential to be able to detect knock at full throttle but it’s also nice to detect engine knock at any engine load. By monitoring engine knock at lower engine loads it is easier to perfect part-throttle ignition timing maps.

For example, the engine knock volume threshold maybe be “10” at full throttle. Just because this threshold is not met at lower engine loads does not mean the engine is not knocking. An engine can knock at partial throttle but the intensity will be lower than at full throttle. It is nice to be able to differentiate between partial throttle knock and full throttle knock.

RPM – Essential

Engine noise increases as RPM increases. The knock threshold intensity will usually be higher at higher RPMs. Knock intensity at 3000rpm will be much lower than at 6000rpm. If we set our knock threshold intensity to 6000rpm there is a good chance we won’t pick up knock at lower RPMs

Ignition Window – Nice to have

Some engine knock detection systems can only measure the signal from the knock sensor during a certain window of crankshaft rotation, something like 10 degrees before TDC to 50 degrees after TDC. This window is where the manufacturer of the knock detection system believes knock will most likely occur. By only listening to knock in this window, sounds unrelated to ignition can be ignored from the measurements.

This should give better accuracy in detecting engine knock and it could also increase the speed by which knock is detected.

Knock By Cylinder – Nice to have

Fuel and air flow is rarely even across all cylinders. Being able to optimise the ignition calibration on a per cylinder basis should improve power and efficiency.

Frequency Calculator – Nice to have

There is a theoretical knock frequency based on cylinder bore. There are knock frequency calculators available online. The actual knock frequency received by the knock sensor may differ from the theoretical frequency due to the location of the knock sensor on the engine, the type of knock sensor, the routing of the wiring and other installation specific factors.

A feature that allows the user to identify the actual knock frequency of an installation can be very helpful to calibrate the knock detection system.

Normal Engine Volume Calculator – Essential

To identify engine knock we must know what is the normal knock sensor volume when the engine is not knocking. A feature which allows us to calibrate the knock sensor system for the normal knock volume is essential.

Interpolated/Variable Knock Volume Threshold – Nice to have

This feature is related to the system being able to read engine load and RPM.

I wrote above how the knock volume threshold can change according to engine load and RPM. A system which has an adaptable knock volume threshold according to these conditions should be more accurate at measuring knock in more engine operating conditions.

Visual/Audible (Buzzer) Output – Essential

When we are not using headphones or listening to the engine generally, we need an indication of when the engine is knocking. It is essential that the device can alert the operator of engine knock either visually or audibly.

Output Signal to Engine ECU – Essential

This feature is a nice to have for calibrators using the OEM ECU but arguably it is an essential feature for engine’s using an aftermarket ECU (or an OEM ECU which can accept analog inputs) which use the signal to adjust ignition timing in real-time.

An engine knock detection system which can output a signal to an engine ECU to indicate engine knock adds an extra layer of engine protection and can help the calibrator perfect the calibration by looking at datalogs from the engine ECU.

Variable Output Signal to Engine ECU – Nice to have

As above but instead of a fixed signal being sent to the engine ECU to indicate engine knock, the engine knock detection system has the ability to send a variable signal to the engine ECU to indicate the severity of the engine knock, not just a “yes/no” the engine is knocking, signal.

Permanent Install – Nice to have

If the vehicle user always has access to the status of engine knock, the vehicle user could identify specific conditions where the ECU calibration may not be optimal or perhaps identify if the engine is developing a problem, be it a fuelling issue, a timing issue, a fuel quality issue and so on. Logs from the engine ECU could also include the knock data. This ongoing monitoring is only possible if the product is mounted in the vehicle permanently.

If we can not mount the device in the vehicle permanently (and unobtrusively) we lose this ability to monitor the knock detection system, output.

Wiring Loom and Knock Sensor – Nice to have

A pre-made wiring loom may make installation easier (assuming the loom is long enough). Likewise a supplied knock sensor may be easier to install versus having to tap in to the existing knock sensor which may have difficult access.

Software – Nice to have

It may be nice to have PC/laptop based software to analyse the knock sensor signal separately from the engine ECU software

Audio Connection – Nice to have

Being able to tap into the audio signal from the sensor using the product may be a bonus to some.

Price

OK, price is not a feature but it is a factor.


Scoring – Engine Knock Detection

For the “Essential” features, products get 10 points if they have it, 5 points if they kind of have it, 0 points if they don’t have it.

For the “Nice to have” features, products get 3 points if they have it, 1 if they kind of have it, 0 points if they don’t have it.

Price score. 1 point if over 1000 dollars, 2 points if over 900 dollars etc to 10 points if over 100 dollars

The Scores

FeaturePlex Knock Monitor V3Phormula KS-4MoviChip KSC2TunerNerd Elite
Engine Load Input3000
RPM1001010
Ignition Window3000
Individual Cylinder Knock Detection3000
Frequency Calculator0030
Normal Volume Calculator10101010
Variable Volume Threshold 3033
Visual/ Audible Output 10101010
Output Signal to ECU 10101010
Variable Output Signal3303
Permanent Install1131
Wiring Loom & Sensor3313
Software3313
Audio3303
Price ($ Equivalent 20.1.2022)1075400270415
Price Rating1797
Total Score66506063

The Results

How do the products score with regards to features?

First Place – Plex Tuning Knock Monitor V3

As expected, the Plex Tuning Knock Monitor V3 came out on top despite being over twice the price of the next most expensive engine knock detector in the comparison. When you need a tool that can give you OEM levels of features for an OEM like level of calibration the Plex Tuning Knock Monitor V3 is far ahead of the other products in this comparison. Perhaps there exists a similar level of sophistication inside standalone ECUs, for example the Motec M1 but that discussion is for another article.

Some stand out features of the Knock Monitor V3.

Individual cylinder knock detection can be very helpful when you need to get the absolute maximum out of the engine. It can also be helpful in diagnosing potential problems with the engine hardware.

CAN connection and the software allows very sophisticated analysis of the calibration

Downsides

The unit is relatively large, having it permanently mounted on the dash may not be for everyone. If you are not looking for OEM level calibration the unit may be overkill.

Second Place – TunerNerd Elite

The TunerNerd Elite looks to be a very complete solution, it includes wiring loom, sensor, Windows software, datalogging inputs and an audio ouput.

Main Pluses

The Windows software looks to have a lot of options and is nicely presented. It can also display data in realtime. Variable output to the engine ECU is also nice

Downsides

Perhaps not the easiest to permanently install. I think for the visual indication of knock you need to mount the unit where it can be seen and the unit is quite large. Although the Elite is not the only product in this comparison with this issue.

Third Place – MoviChip KSC2

MoviChip seems to have taken a different tack to the other products in this test. They shun audio capability and they also shun any sort of windows software in exchange for having an Android based interface. The KSC2 is the only product in this comparison that is not supplied with a wiring loom or a knock sensor, Although they do supply a high quality automotive connector for the user to populate.

Main Pluses

The stealth install and ability to trigger visual/audible indicators remotely. This is the probably the product most suited to be installed in a vehicle permanently. The in-built frequency calculator is unique among the other products in the comparison, although this could be down to the fact the KSC2 will be used with third party sensors and wiring of unknown origin.

Downsides

The knock output to an ECU is binary. It will tell the ECU if it detects knock but not the severity of the knock. The other three products seem to be able to output the severity of engine knock. For any data analysis you will need to use software from the engine ECU or a specialised datalogging product.

Fourth Place – Phormula KS-4

The reason the KS-4 does not score higher is the lack of an RPM input. An RPM input is on the “Essential” list, not having is a big scoring handicap versus the other units. I have not used the KS-4 but I am not sure how it can measure knock accurately at lower RPMs without this input. This omission seems a shame because the unit seems robust in all other areas. It comes with a wiring loom and sensor, it seems to have a variable output to feed to an aftermarket ECU and it can power an external knock indicator such as a light or buzzer.

Main Pluses

It seems to be able to output a variable knock sensor to an ECU. This could allow an engine ECU to take into consideration RPM and load.

Downsides

As detailed above, the lack of an RPM input could massively compromise the engine knock detection abilities of the unit, in my opinion.

This page was last modified Jan 20, 2022 @ 6:15 pm

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