Rick

Not so many years ago, det cans werre considered by most the best way to detect detonation. Det is often unaudiable, so mappers relied on the early stages of knock or audiable preignition, and then would back off the timing from here.

Modern OEM ecu's use knock snesors and are able to constantly adjust engine parameters to use the most possible ignition advance while keeping the engine safe. I'm interested to see what the mappers think of current electronic knock/det detection systems. As you can't hear det, these devices offer the possibility of picking up the harmonics of abnormal combustion before the human ear does.

Any thoughts?

Rick.

R4N SS

iTrader: (6)

interesting topic...

The DIVA

iTrader: (3)

I`m very interested by this too, we are noticing that the manufacturers are using more knock sensor channels now to detect multiple areas on the engine....we have found 4 sensors so far on my mates new R8

AlexF

If you want to know more about this try seraching the net for Ionic Knock control like the BMW E60 M5 runs...

Alex

foreigneRS

if they're using the old style of knock detection, i.e. 'audible' then they can 'tune' the ecu to listen to the frequency range specific to that engine. universal kits do not usually have that ability

ECU Monitor Enthusiast

iTrader: (1)

FYI,...

Dont treat knock sensors like human ears they do NOT detect sound.

Most kits convert a pulse into an arbitary audible noise do you can hear it.

They are in fact accelerometers, I.E they detect movement and convert these to electronic pulses of varying frequency.

By use of electronic filters and timing alogrithms, knock is detected as a signal that occurs in a very wide frequency range within a certain time frame for a particular cylinder.
This partly removes mechanical noise from false triggering the sensor.

The more sensors there are on an engine, the better overal accuracy and repeatability a system will have.

ION knock sensing as suggested above is a totally different technology and in fact doesnt detect knock directly itself.

CombatSapph

Am I also correct in thinking that maximum advance without pinking does not always (in fact rarely) equal maximum power. So advancing to knock then backing of a couple of degress doesn't mean max power.

wirralphil

Sorry to sound dumb but what is Det?

Is it when a piston is on the upstroke and their is an early ignition?

GARETH T

you are correct!

ion sensing so very cool! takes a fast processor though i would guess!

Chip

iTrader: (3)

Did you mean


If so, then yes absolutely.

markk

iTrader: (2)

so bringing the YB into this, as we all know that a knock sensor in the bottom of the block is a dumb idea, where would you be looking to position a knock sender on a yb, top of the block? lower section of the head? to get as close to the combustion chamber as possible?

Chip

iTrader: (3)

For a conventional externally mounted knock sensor like the YB, it really doenst matter much, the whole block rings like a fucking tuning fork anyway.

markk

iTrader: (2)

the letters NVH was made for the YB !!

jammy86

Nah was made for the CVH, but they dropped the C and made it N so it wasn't the same as the engines name

I've been told by a fairly reliable source that a standard Bosch sensor screwed in to the back of the block, ran in to a laptop and listened to on some cans should be sufficient as long as your not going to tune to max det limit.

JAmes.

Chip

iTrader: (3)

Err, what does the laptop bit do? surely if you have the cans on, you dont need a latop? Ive certainly never use a laptop for knock detection and havent had a problem yet on any of the many cars ive mapped.

jammy86

Laptop amplifies the signal from the sensor. I expect you've had no problems as you've used a full knock sensing kit.

JAmes.

ECU Monitor Enthusiast

iTrader: (1)

Actually it doesnt in todays real terms of cpu performance.
It uses specific ASIC hardware and a DSP to do it.
Besides it doesnt detect the pressure wave on the current cycle.
It uses the info to correct the next cycle so has time to process and is cheaper to implement.
All engines can tolerate the odd sporadic det event and infact all closed loop ignition systems have to generate det in order to know where the limit is so it can self adjust away ! (PID loop of sorts)


The only amplifier in any lap top is the audio one for the speakers which is no use for this application.
More likely its used as a data logger.

jammy86

Sorry, perhaps I should have been more specific in my first post.

Typical knock sensors sense the vibrations (noise) that is caused by the detonation. Ideally you would place this at a point of the block which resonates the most at the knock frequencys (4kHz or something like that?). Lots of knock sensors are simply microphones which have a frequency filter which only the knock bandwidth to pass (well the rest of the sound passes but is filtered, ie. quieter). You plug the knock sensor into the microphone input of the laptop and listen for the knock which should sound like a static click, as if you were plugging and unplugging a speaker connection on your hifi. You still have you uses your ears as oppose to a nice light to tell you its knocking.

JAmes.

SillyFezzaMk1

iTrader: (1)

Ok so what are peoples recommendations on an in-car det gauge or visual meter??? I know they're out there so does anyone have 1st hand experience with one?

Can't be driving around with a knock sensor plugged in to the stereo now can I!

Dan

AlexF

Phormula are good...

Chip

iTrader: (3)

A 0-5 volt output from a decent knock detection kit, into an autronic SM4 ecu, with a table with allowable values mapped RPM vs BOOST, with a light that comes on if they are exceeded.

Thats the best visual system I can think of as its fully mappable to your specific engine, not based on a shitload of assumptions.

Chip

iTrader: (3)

Looks a nice bit of kit but would be NO use at all on a trackday or while driving on the road, ok for mapping but not for telling you if something has changed since IMHO

AlexF

They have audiuable and visual alerts....

Chip

iTrader: (3)

Yes, which arent mappable.

All you can do is set a value that if it goes above it tells you, you cant set different values at different points, which means that given that at some points in the range the knock value it gives is lower for det than it is at other points for normal operation, its of very limited use.

So like I said, better to map it on something like an SM4

Big Will_

Lol - when the Phormula goes off to warn you it's picked up more than acceptable det it goes off properly

Has a good range of adjustment on it too

Rick

Chip, i think you may be oversimplifying some of the later sensors. They are designed to take into account the varying RPM an engine works at.

Will, do you use the Phorumla? Does it pick up things that cans can't?

Rick

GARETH T

are knock sensors now active then? as apposed to a passive device

AlexF

Not on BMWs - they are normal accouctic type...

GARETH T

TBH i havent heard of any active knock devices

Chip

iTrader: (3)

Yes but its defining what is acceptable that is the problem

Define "good range" can I set it so that its different at different boost levels and at different rpm on a 3d map?

No, thought not, lol

AlexF

Chip thats more than most people will ever need!

Normally you tune an engine not to det (I'll be specific - I map like that) and then monitor it for "safety" reasons. Manufactures are the ones who usually map the car right into det and then use knock sensors to deal with it.

alex

Chip

iTrader: (3)

Fair enough Alex, depends what you are wanting to do I guess.

Personally though im of the opinion that if people have a gauge in front of them that tells them half truths they end up ignoring their other senses.

Its a bit like a narrow band lamba gauge, if people have one and it shows rich, they assume their car isnt lean, when on full boost it may well be, and they often ignore other warning signs like excess exhaust temp telltalls because they have a gauge telling them its rich so it cant be lean even if other things hint it might be.

Rick

up

AlexF

True - but if there is det and the driver backs off (eg poor quality fuel) then it might be worth it

Alex

GARETH T

i always like reading your replys simon!!! top marks

SS1

iTrader: (3)

Stu's old shonky has a knock sensor in the dash, if your in work tomorrow could you ask him where the sensors are based on the engine as a mate of mine asked

Ive always pondered where and whats the limit for the BLUE LED

pa_sjo

I bought one of these once but never got round to it to test/compare to proper cans...

http://www.turboxs.com/more_info.php?ID=212



Not expensive, possibly worth a shot?

lead_foot

iTrader: (1)

How much was that?

pa_sjo

Not sure, but under £100 from the States. I wouldn't use one for tuning purposes, but might be useful as an post-tune warning light. It'd need testing though.

Knock detection is a very complex thing and it's something OEM's spend a fortune on in R&D. I believe the BEST way to do it is to directly monitor cylinder pressures within the relevant time window but it's not practical to have a pressure sensor in each combustion chamber (although this is done during some engine R&D).

Chip

iTrader: (3)

Those ones at least make an attempt a noise curve over the rev range, all be it one only drawn from two straight lines.
Look great for the money IMHO