Anti-Detonation System?

[jyl]

What are some ways of detecting and preventing detonation in a high-compression 911 motor that has to run on pump gas but lacks a factory knock sensor (e.g. a Motronic), without a expensive aftermarket engine management system (e.g. a Motec)?

Is there such a thing as an aftermarket knock sensor that can detect detonation and do something about it (e.g. alert the driver, trigger water injection, cut off fuel, etc)?

Does a CHT/EGT monitor detect detonation? Will it do so in time to alert the driver to lift off before the engine is damaged?

I don't know much about this and don't have an engine project underway, so I am just asking to see if there are good ideas out there. Basically, I'm curious.

[s_wilwerding]

I don't have a definitive answer, but I don't think there are any aftermarket knock sensors that you could easily add to a Porsche. You have to figure that the knock sensor would have to be integrated with the engine management software to vary ignition timing when knocking occurred. This would require at the very least a remapped ECU, which may or may not be able to integrate with an aftermarket knock sensor.

I suppose anything is possible, but I doubt this would be a cheap or easy project to undertake.

[ChrisBennet]

J&S Safeguard has a knock sensor that retards the spark on a cylinder by cylinder basis.
-Chris

[89turbocabmike]

John, from what I've read about this, to be truely effective, the knock sensor needs to be tailored to the particular "noise" characteristics of the engine it's on. I'd love one for my 911 turbo. I did a knock sensor update on a turbo'd VW GTI I had years back which was a successful and popular upgrade because later VW motors(similar motor) came with one that could be retrofitted. Regards, Michael

[ChrisBennet]

Somebody on this list is using a J&S, I think it is "350HP930".
-Chris

[RickM]

From what I've read it seems the 911 engine is too noisy for a knock sensor. I believe BeepBeep tried it (or knows of someone) and found it to be ineffective.

Here's a related thread.... Turbo Carrera making real progress, question for those who've been there...

[jyl]

Will a EGT/CHT sensor detect knock? In time to avoid damage, that is?

[Chuck Moreland]

Perhaps the 3.6 sensor could be used, with an aftermarket ignition.

[tsuter]

The only fool proof way to detect knock is ionization across the gap. Once knock is detected then the retard formula can kick in as J&S Safegard or others use. The key is knock detection. The change in resistance across the plug wires caused by ionization is detected by the ECM. Different wire lengths (resistance) must be accomodated.
With current EFI ECM capability, people often unintentionally disable their knock retard features when they install "low resistance" wires thinking they are improving ignition!

[ChrisBennet]

While Saabs way of using the spark plug is ingenious and effective the method Porsche/Bosch uses work well enough. The 911 engine is not "too noisy" for the factory knock sensors so it must be possible. When I inquired about the J&S system they told me they were being used on a few 911s.

I looked into using the factory 964 sensors on my 3.2 (3.4 twinplug). the 964 motor has a "bridge" that mounts to bosses on the cylinders. These bosses aren't present in earlier motors so I didn't pursue it further.
-Chris

[RoninLB]

Originally posted by jyl
Will a EGT/CHT sensor detect knock? In time to avoid damage, that is?

I'm using an aircraft computer for EGT & CHT monitoring.. maybe this will help

[jyl]

Ronin LB, am I correct that your (incredibly cool!) J.P. EDM computer can be set to give you an audible alarm at EGT/CHT values that imply detonation or preignition? So that you are alerted even if you are not actually watching the EDM - for example, when you're on a track concentrating on driving?

[MotoSook]

That one is going into the "good stuff" file Ron! How about a thread with the setup and a show and tell???

[bell]

i've seen pics of ron's setup....VERY impressive stuff and super cool to boot

[RoninLB]

Originally posted by jyl
So that you are alerted even if you are not actually watching the EDM -

there is a screen alarm, and a low amp output for an alarm dash lite.. because I get blind, deaf, and crazy on some of my rides I'm going to use the low amp lite wire to trigger a relay, to trigger a FD 110db+ blaster.. mostly because of my relatively loud exhaust and ear damage audio habit..

[RoninLB]

Originally posted by Souk
That one is going into the "good stuff" file Ron! How about a thread with the setup and a show and tell???

it's a kinda mindless install.. and its console mount doesn't even attract attention.. the EGT probe wires were kept under the engine, riding in indivudal small dia rubber fuel lines.. the CHT probe wires from the spark plug gasket/sensor ride outboard of the engine. there are 2 electrical connectors for easy enging drop.. the beauty of the install is in the hidden from view install neurotic details.. not much else to offer, I think

[RoninLB]

Originally posted by Souk
How about a thread with the setup and a show and tell???

still thinking about you, Souk..

right now the car is being prepared for some jewlery.. so the
EDM 700-6c hasn't gotten much attention.. I was supposed to install the rear window today, BS, etc.. so I'm still in a humble situation in trying to understand what this unit offers.. and no living with this for awhile. maybe next spring.. but some morning stretches of 500mi or less is a done deal..
and to put this unit on the track with someone tommorrow needs someone who knows about the 911, and is an aircraft mechanic, to set this thing up.. I still figuring out what questions to ask JPI tech.

and Guys,
I do enjoy having this new toy around.. just like the little kid in a candy store.. With the education that a computer offers.. I gotta Luv it...........Ron

[Steve W]

I believe the 944 turbo uses a Motronic dme with a knock sensor built in (KLR). Its DME is not too different than the one in the Carrera, so imagine the possibility of incorporating one with the associated software changes. Just remap the chip the same as the Carrera's.

Another cheap and practical knock sensor system would be the SAAB APC system which you could pull out of any mid 82 on up SAAB 900 or 9000 Turbo. I can just go to my local Pick-A-Part and gut one out for about $10. It's a grey or black box under the rear passenger seat in 82-86 cars, and black or red on the side of the engine compartment in the later cars. The knock sensor is center on top of the engine block bolted down with a 10mm? bolt. The box incorporates three inputs, knock sensor, rpm, and boost pressure to determine the pulsed output signal it sends to a 12v selenoid which controls bleedby for the Turbo's wastegate release pressure. The box has three adjustable pots, that determine the output signal based on the sensitivity to the knock sensor, rpm, and boost pressure. All you really need to use is the knock sensor and hook up power and ground, and use the selenoid output for whatever you want (water injection, ignition retard, or to a led to indicate predetonation).

[350HP930]

Originally posted by ChrisBennet
Somebody on this list is using a J&S, I think it is "350HP930".

Thats right, and I can certainly say it works.

When my andial fuel enrichment system took a dump you could tell it did its job far too well at high boost by pulling the timing back so far I initially thought I had problems much worse than A/F.

After 130,000 miles of high boost and agressive ignition timing in a hot area like Florida my pistons show absolutely no signs of detonation damage or abnormal wear.

Many factory system use acoustic knock detection so there is nothing wrong with the concept. And while some people state that an air cooled engine is noisy, they are referring to the ability for it to transmit its internal vibrations to the air. Internally a porsche engine is no noiser than any other six cylinder engine with overhead cams. On top of this the acoustic sound of detonation can not be confused for valve train noise.

[RickM]

Bump....BeepBeep, any comments?