Why Is A 'knocklink' Essential Scooby Kit, But Not Skoda ?

[Fabpreza]

I was reminded of this when people started talking about SUL /Optimax etc :-

- On tuned Imprezas, an essential piece of kit was (is) a knocklink device which warns of detonation and potential engine damage.

I've never heard this mentioned for Skodas (1.8T).

So, is the VAG 1.8T engine / ECU better than the Subaru's in adjusting to higher boost / different ron fuels / stenuous use ?

:confused:

Just want to know the reason !

[devonutopia]

Glad you explained what it was - I was going to start with WHAT is a knocklink?.. Although, I don't remember any alert going off on the RPM tour when Gossy's scooby's turbo went spectacularly... :(

I guess VAG assume their 1.8T's don't get as much abuse? - or that the engine management will cut out any problem areas before an explosion becomes imminent? Interesting Q that...

[mannyo]

Could have done with one of those things in Germany, back in august.

TaviaRS was following at erhmm MPH, when just pas bonn on the autobahn, lots of noise from under the bonnet and no power. The engine was det ing badly. When we arrived at the destination Jon asked me what all that smoke was coming from the exhaust. Seems I had put a whole tank of duff fuel in by the hotel near cologne.

[Tech1e]

VAG petrol cars do have 'knock sensors'.

They are bolted onto the engine block and contain a pietzo crystal which alters signal when vibration or knocking is felt. This in turn controls you ignition timing via the engine ECU.

[Fabpreza]

Techie

Imprezas do as well (I'm 99.9% sure), but if you visit Scoobynet (as I used to), most owners who tune their cars beyond (say) 240bhp with a remap, decat, induction etc, also fit a separate knocklink device.

This warns by a series of lights how much detonation is going on. I've not heard of anyone needing to fit one to a 1.8T Octavia yet. WHY IS THAT ?

p.s. My Impreza's engine self-destructed due to detonation (95% sure) caused by degrading Dogimax (90% sure), but I didn't have a knocklink fitted so will never 'know' for sure.

[Steve vRS]

A lot of Scoob owners hit a knocklink when they are tuning their cars due to turbo engines being particullarly prone to detonation. The Impreza ECU monitors 'Knock' which it uses to adjust timing so that the engine is always running at it's most efficient. However, the Knocklink is more sensitive to knock and also gives the driver a visual warning of detonation. I believe that they use a Bosch sensor as part of the kit.

The question remains, do highly tuned VAG 1.8T engines need the extra protection offered by a knocklink?

Steve

[Tech1e]

Ive not seen alot of 1.8 T engine fail due to detonation. Might be due to fairly low amounts of boost pressure and small turbos on the whole. (compared to some Jap cars)

And dont forget most Jap cars are supposed to run on 100 + RON fuel which they do in Japan which isnt really availible over here.

[KLB]

VAG 1.8T engines definitely have a knock sensor (tuned piezo-electric type).

I don't understand the point of a "knocklink" (as described here) - it sounds like an LED display showing "this is how fast your engine is being destroyed".

What's the point in having a display which shows "knock levels"? The ECU should be reading the knock sensors and retarding the ignition so that it doesn't happen.

[Neo_VR]

i think the knock sensor on the impretza is only a slow acting one and the ecu takes time to adjust..

mind you.. VAG is miles ahead in terms of engine and electronic technology! does the prezza have a "limp mode" if it overboosts?

EDIT: just thought.. with the prezza having horizontally opposed cylinders detonation will put more stress on the rods/crank/bearings then in a standard 4 pot..

just my 2penneth

[Steve vRS]

Scoobynet knocklink question

Steve

[Stuart_J]

As a general rule Scoobs go bang, Skodas dont. As to why scoobs go Pop there are endless discusions on Scoobynet with various conclusions but the fact that knock sensors, exhaust temp gauges & Oil pressure gauges seem a common fit means the Engines are fairly stressed when tweaked with. Also should they let go they cost a small fortune to fix.

[Alex]

so the infamous japanese quality it not as it seems then?

[Fabpreza]

Originally posted by Stuart_J in this post

As a general rule Scoobs go bang, Skodas dont...but the fact that knock sensors...seem a common fit means the Engines are fairly stressed when tweaked with. Also should they let go they cost a small fortune to fix.

That sums up my reason for the thread

Mine (a UK car with FSSH and super-duper oil) would have cost

[DaveU]

Originally posted by fabia in this post

so the infamous japanese quality it not as it seems then?

Well I wouldnt say that exactly... cars like the STI are pretty well tuned to begin with and as someone pointed out - are designed to be run on 100+RON petrol which we dont get over here... The Knocklink is more a paranoia gauge I think - I never fitted one in mine but then I only had a zorst + induction - never got it remapped. I ran it on Optimax (when it was 98 RON) + octane booster and it never knocked.

[Andy Tang]

Hi guys,

Some of you know me from Scoobynet!!

Too much boost, bad quality fuel, your engine goes bang!!!

Seriously, the Knocklink has two parts, the sensor and the display.

The sensor is a small microphone that mounts onto the engine block (much like any other knock sensor) and listens of specific frequencies, which are in the range of pre-detonation.

The display has a series of LED's which show how severe the noise was! So green for normal, amber for warning, and a big red one!!!

I had a UK Impreza, running a big turbo, FMIC, filter, de-cat, etc, etc. The car had a standard block and fuelling system and ran 1.3bar of boost.

The knocklink would stay in the green as long as I ran on Optimax! (The car had a Link ecu which was mapped to run on Optimax!) I used BP SUL once and the Knocklink lit up like a christmas tree even on part throttle! A cap full of octane booster and everything was normal again!!! I believe that the knocklink saved my engine that day, from very low octane SUL!!!

I believe they are invaluable on turbo cars! If I were to start tuning another turbo car, I would invest in a Knocklink straight away!!

Cheers

Andy

[tavia4x4]

Hi Andy, welcome on board!

:cheers:

[Clarey]

Hi Andy and welcome to briskoda.net,

For those who are wondering what a knocklink looks like i have found some old pics.

( EDIT :webspace isn't working, see attachments)

The knocklink lights located under the fuel guage:

The Knocklink sensor fitting location:

The Knocklink sensor fitted in position:

Can be fitted to any engine not just subaru, only requires 12v to work.

When fitted to my STI 3 using standard ECU, it occasionly lit up big red using SUL, so octane booster was needed to be safe.

Happy VAG man now the scoob is gone, got too paranoid about the scoob in the end.

Phil.

[Clarey]

The knocklink lights located under the fuel guage:

[Clarey]

The Knocklink sensor fitting location:

[Clarey]

The Knocklink sensor fitted in position:

[Neo_VR]

Thanks for the info... yer learn something new every day dontcha!

so the knock sensor in a scoob is purely for efficient running.. but only has a limited range of ajustment..

no doubt the VAG one will be much more responsive, and could put the car into limp mode if detonation was really bad..

ive heard of a 225 bhp engine wind back the boost/bhp to about 160 on a rolling road due to heatsoak, so it wouldnt suprise me.

[Disco@Impreziv]

Nice one Andy, good to see you here:D

IMHO there are 3 main reasons as to why a knocklink is more valuable on a scoob than most cars.

1) In non-remapped form, a Scoobs ECU runs as perilously close to the knock threshold as it can. The engine design and compression ratio makes ignition advance critical to torque delivery. Obviously adding decat exhausts, inductions and then more critically boost controllers means the ECU can be running closer to that threshold than if often thinks.

2) Because of the boxer design of the engine the dynamic movement of rods, pistons and also the bearing loads mean that said components are prone to failure from lower levels of det (knock/pinking)...(apparently)

3) When remapping/tuning a car obviously having a display of knock readings is critical due to above sensitivity to knock related issues.

There is a knock sensor as standard, the ECU actually sets itself by running ignition until it detects knock and then corrects itself by a few degrees.

Given that its so susceptable to knock I personally think that any tuned Impreza should have a Knock Link for warning purposes. (That said it didn't stop mine going pop!)

I think before I start playing with the Skoda I'll probably fit one to that also, purely for peice of mind.

Disco

[Fabpreza]

Glad to get some more meat on the bones on this topic, as I did wonder.

For what its worth, I have a lot more confidence in the Octavia/1.8T/Jabba/unleaded combination than I did in the Impreza/***tek/Optimax combination, and won't be fitting a knock link.... that's unless I lose an engine in an Octavia as well !

[Steve vRS]

Not a fan of ECUTECK?

Steve

[Fabpreza]

Steve

It was excellent while it lasted (probably better than PPP) but it was either that or the fuel (Optimax) or a combination of the two that caused "one or two teeny-weeny problems with the bottom half of the engine and its contents"