Knock alert

[sawood12]

I've just ordered a DME/KLR chipset and 3bar FPR from Promax which when fitted means i'll have the Promax level 2 kit fitted (i've already got the DPW). My research on off-the-shelf chips has shown that the knock/overboost protection the standard KLR chip offers by being able to retard the ignition is lost as the KLR cannot provide this function at elevated boost levels. Even though I know that there is now enough people running these off-the-shelf chips to prove their safety but I still don't like the idea of loosing that extra level of protection. I wondered if it would be possible to run some wires from the knock sensor to a light to alert the driver that there is knock happening so they could at least ease off the throttle??

 

[Fen]

I don't think boost matters to the KLR. My understanding (based on my own experience playing with a BE and differing grades of fuel) is that it detects knock pure and simple, so if the fuelling were correct for 36psi the KLR would let the car run 36psi, but if the fuelling were weak with no boost at all it would do its stuff.

 

[Diver944]

I may be wrong but I was always under the impression that you'll lose the overboost protection but that knock detection is still there. Give Andrew a call and I'm sure he'll let you know for sure. I know he was working on a chipset that keeps all the factory protection features but that allows boost up to 1.2 bar.

In the meantime there are a couple of knock indicators on the market - a google on 'Knocklink' brings up loads of sites

 

[Fen]

With respect, Paul, I already explained to Andrew on here that from my experience boost is not what is measured and I have since seen him post to that effect on Rennlist. I don't know why it would be designed to care about boost when boost is safe provided fuelling is correct, all that would achieve is hobbling the performace potential of the engine (which I guess is quite possible knowing Porsche and anything but the 911).

 

[berg944]

but if the fuelling were weak with no boost at all it would do its stuff.

I can confirm the mixture will trip the "knock sensor" as mine tripped and the engine went into "reduced power" mode when my inter cooler pipe was blown off (no boost to inlet). This was overfueling not a weak mixture.

Mike[:'(]
Just thought it could be the "reduced power" part of the programme that might change when swapping chips?

 

[sawood12]

I too thought that the ECU doesn't care about boost at all and just monitors knock but the term 'overboost' was one of those terms that is used to describe the effect and not the cause. In my mind the only thing that initiates the timing retard (and clycling valve to divert full boost signal to the wastegate if it is still connected) is the KLR computer who's sole purpose in life is to look for knock and adjust timing to suit and if knock becomes unmanagable it switches to 'overboost' and retards the timing fully (6 degs I think). From the reading i've done so far I was under the impression that the only reason why the KLR chip has to be replaced in these off the shelf solutions is to effectively disable this function because if the KLR sees boost levels above 1 bar it automatically initiates the knock protection whether or not knock is detected. Obviously in the majority of cases where these chips are used people are pushing boost up beyond 1 bar so the standard KLR chip cannot be used.

In any case assming the knock sensor converts the piezo electric signal to a voltage then it should be possible to splice into the loom, pick up the right wires and rig up a bulb or something to light up when the voltage signal from the knock sensor signals knock?

 

[AndrewS]

Hi Scott,

Knock induced retard is a function of the KLR. If the knock sensors are working on the car; this function is invoked by the KLR detecting the knock signal and passing the instruction to the DME to retard timing.

With the ProMAX chipset, what you won't have is over boost protect. This is induced if the knocking increases to the extent that ignition retard does not cure it. The ignition is then retarded a full 6 degrees and the cycling valve switched to reduce boost. There is an over boost value on the factory DME chip also, this corresponds to a maximum boost tolerance value. On the ProMAX chips this is increased and the over boost protect is disabled as the chipset is designed to run beyond the KLR map sensor capability which is 1.0 bar (1.2 bar). There is also an additional temperature induced ignition retard if the ambient temperature at start-up is very high. This presets the whole ignition map with a fixed retard constant.

For those that want to retain the over boost protect function, we offer the SciVision chipset which retains all the original functionality but is limited by the factory KLR map sensor (1.0 bar). The ProMAX 1.2 bar chips offer increaseed performance as they can run with more boost (as was seen on May 20th with cars fitted with Level 2 on the Dyno).

Regards,
Andrew

 

[sawood12]

Andy, thanks for the detailed explanation it ties up with previous conversations i've had with you and other things i've read on off-the-shelf chips. Although I am confident about the safety of these chips as long as you use decent fuel I was just wondering if there was any other way that I could rig up a signal if the car did, for whatever reason, get into the situation where the normal knock control was not stopping the knock situation. If a lamp could be rigged up to illuminate when the KLR tells the DME to go into 'overboost' mode then at least I would be able to come off the throttle and pull over.

By the way I fitted the Promax Level 2 chips & 3bar FPR today. The install was basically a doddle - the only minor issue I had was in dealing with is all the extra boxes and wires that are hooked into the ECU for the immobiliser where the installer wasn't very neat and tidy so I had a bit of an untangling job to do. I took a good few runs to work upto the 1.05bar I want to run on initially and first impressions are that the sudden wave of boost I had previously has been greatly tamed - I wouldn't say the response is lag free but the boost definately starts to come in much earlier and ramps up in an ever stronger wave rather than a step change from nothing to all hell breaking loose. It should be alot better in slippery conditions. Also the car seems to have a noticably more to give above 4500-5000rpm than before where the K26/6 starts to run out of puff. Previously in this region the throttle response was a bit lumpy and lack-lustre but the improved fuel mapping in the Promax chips seems to be much better than the standard chips - this should make life a little easier on the motorway. I havn't noticed a massive increase in accellaration but i've not really driven it much yet and I suppose with the boost now feeding in in a much more civilised manner the extra power increase might be disguised a little.

Now I can't wait for next years Weltmiester rolling road day so I might give them a ring and see if I can get the car on the rollers in a few months time to do the back to back. I'm expecting around 270bhp (give or take a few HP) from my current 240bhp. Big thanks to the guys at Promax for being very patient in answering all my questions over the past few days on the install.

 

[Indi9xx]

The knock sensor in the 944 turbo is designed to be there "just in case"... For example just in case boost shoots up way too high and knock occures... at that point the knock sensor in the standard setup with inform the KLR, which will then pull back boost with the cycling valve.

However, this is designed to be a a bit like an ejector seat in a jet fighter.. not something to be relied in, but something that in a freak event will save your bacon.

By the time the knock sensor will trigger, your already into detonation in great big fistfulls, which is why a good dyno tuner does not just plug into the knock sensors to know if he is pushing things too far, and why also a good dyno tuner will not program a chip that will see the knock sensors firing during heavy use... In an ideal world, the knock sensors will not ever trigger.

If I had my way, knock sensors would bring on a big "PANIC NOW" light on the dashboard so further investigations could be made.

All manufacturer and aftermarket knock warning systems tell you too late, which is why dyno tuners use various methods to make sure they know when knock is about to happen, rather than it has just happened. This includes knock sensors and even combustion ion detection, which both tell you only that knock/detonation is happening.

The other important issue is that not many people, including some chip tuners I have spoken with, understand there is actually several types of knock/detonation, including pre-ignition and sonic wave knock to name but two of about 5 types. Not to mention the various combinations of causes.