Knock Sensor question

[SVXRide]

Originally Posted by Evil One

Making a few dyno pulls with high octane in the car and monitoring it for AFR, audible knock, and temp *engine, induction, and exhaust would be best*... shouldnt cause damage but would give further insight to the performance of the KS and possibilities to work around false positives.
Driving it you feel the car starting to respond and then essentially falling on its face, compared to the pull it should have.
It isnt even my car and all I could think of was how to get past this stumbling block.
I can imagine how it must be for Bobby and Tom.


Jim

Yeah, what Jim said
-Bill

[NiftySVX]

Originally Posted by Trevor

Please advise in full regarding the knock sensors now in use. I have not seen any information in this regard and the subject is of considerable interest.

I have bookmarked this thread and will most certainly pull out my books so i can describe them accurately when i return to my parents home for thanksgiving, I can't remember how they work off hand, only that they are different and were said to be more accurate and compact, and i believe the type of signal they generated was very different.

[svxistentialist]

Originally Posted by Trevor

There should be no reason for the knock sensors to react to noise from a blower. A weight is incorporated so that they are not sensitive to anything even remotely within the audio frequency range. Furthermore they a mounted to a large mass which would damp out extraneous indirect vibrations.

What you are saying here Trevor may be correct in theory or at least desirable in theory, but it conflicts with the observed facts.

Graham had this problem with his Eaton blower. The ECU was pulling timing in a bad way. Initially we thought it was actual detonation. We discussed it with Lan. Some of the theories even included surface imperfections in the ceramic coating on the head contributing to localised hot spots. Bear in mind most or probably all of the US installations were using stock compression ratio. Graham was using a built engine with CR at 8.0 to 1.

The answer was more mundane. It was mechanical vibration picked up by the sensors as sicksubie and Evil One have noticed and deduced.

The actual source of the vibration that the sensors were "hearing" was the drive pulley for the blower. It had a loose key that we were aware of and eventually fixed.

The proof of the pudding was when the installation was put into my Version L, and everything tightened down, no loose pulley. The timing is not being pulled, full power all round.

As Trevor asked fellas, will it be possible to substitute more modern knock sensors in place of these piezo ones we currently use? Will the signal range be correct for the ECU to interpret?

If this made an improvement in a reduction of false positives and stopped the timing getting pulled, it would be worth the cost of the change.

Joe

[sicksubie]

One othe thing tha might add more to the blower vibration/niose theory is that on 9psi the car felt faster. That could be due to the fact that the blower was spinning slower and therefore not generating as much vibration/noise.....


Just some more info for you guys to mull over

[Evil One]

There could be a couple of reasons for it running better on 9 than 12.
9 is closer to base programming, will have a slightly slower boost ramp with lower overall boost to compensate for... and the aforementioned reduction in blower speed.
The cobras with the factory superchargers dont even have knock sensors.
Part of the reason is that the noise from the eaton supercharger, part of the reason is that they are air-liquid intercooled and run fairly low induction temps stock.


Jim

[svxistentialist]

I'm inclined to agree with you here Jim. I have no idea if you have lowered the CR on the car you are discussing, or if you have installed bigger injectors.

Mine is currently running standard injectors, standard CR and about 6 pounds. My calculations give 9 or 10 lbs as the point at which the stock injectors will be running 100% of delivery rate.

So if you are running stock CR and stock injectors the AFR will be lean at higher than 9 lbs boost and you would expect the ECU to try and compensate for that. With injectors giving 100% it will not be possible to throw extra fuel in to richen it up.

Joe

[Evil One]

As a first step, I normally step up injector size and turn down the fuel pressure. On cars with a boost referenced fuel pressure regulator I watch the AFR and have switched to a variable ratio FPR when it ran too rich/lean in the upper rpm or boost range. This allows for growth in fuel delivery without breaking the bank.
Its a little crude but "can" work very well on many engines.


Jim

[SVXRide]

Couple of SAE papers dealing with knock sensors (unfortunately my membership lapsed a couple of years ago and I've been too busy to renew)

http://www.sae.org/technical/papers/2007-01-1288

http://www.sae.org/technical/papers/922370 (optical fiber knock sensor!)




anyone down in Florida should look into attending this training class:

http://www.sae.org/servlets/pdEvent?...EVT_NAME=C0602

-Bill

[sicksubie]

Joe,

the car is running all forged internals with a CR of 8.5:1. The injectors are 740cc from NISMO. My AFR are good at WOT. Once the pedal is floored they stick at about 11:1-11:3. I cannot say though if they stay in that range through the whole RPM range though at this point. I am hoping to go to a dyno letter part of this week or the beginning of next week. That will give some much needed insight on a variety of things.

[svxistentialist]

Originally Posted by sicksubie

Joe,

the car is running all forged internals with a CR of 8.5:1. The injectors are 740cc from NISMO. My AFR are good at WOT. Once the pedal is floored they stick at about 11:1-11:3. I cannot say though if they stay in that range through the whole RPM range though at this point. I am hoping to go to a dyno letter part of this week or the beginning of next week. That will give some much needed insight on a variety of things.

That all looks good and strong. In which case you would not expect more than the normal amount of detonation to intrude.

However you did not mention charge cooling. Are you using an intercooler?

If you are not, then you will certainly be creating much more heat in-cylinder with the higher boost figure. In turn this will create the conditions for actual detonation. The sensors will detect it and the ECU will pull the timing.

You would expect there to be less of it[or at least be less susceptible to it] at 9 lbs, although it might still be present.

That might be the reason it feels more powerful at 9 lbs.

I'll be looking for the dyno figures, it will be interesting to see those. Thanks.

[Trevor]

Originally Posted by svxistentialist

The actual source of the vibration that the sensors were "hearing" was the drive pulley for the blower. It had a loose key that we were aware of and eventually fixed.

The proof of the pudding was when the installation was put into my Version L, and everything tightened down, no loose pulley. The timing is not being pulled, full power all round.

Joe

Joe,

More acceptable proof would require the installation to remain exactly as is/was, with any adjustment confined to the rectification of the loose pulley. How was it exactly established that the timing was not being "pulled"?

The problem is that all is and has been assumed, based on information which is not absolutely definitive. Furthermore experiments envisaged will not in practice indicate exactly what is transpiring. All is rather hit and miss.

Bill has shown an interesting paper. which indicates that the a knock sensor signal has been used to detect valve operation by analysing the audio signal produced. A special or modified sensor may been involved, we do not know.

I have suggested a means of establishing fact in my post No. 14, which appears to have been ignored.

[sicksubie]

I am going to the dyno the Monday after Thanksgiving. I will be renting it for either 1 or 2 hours and will be fooling around with different octanes as well as the two different versions of LAN's software that I have.

Joe,

It is NOT intercooled but a methanol kit is planned for the future to help in the cooling of the intake charge.

[svxistentialist]

Originally Posted by Trevor

Joe,

More acceptable proof would require the installation to remain exactly as is/was, with any adjustment confined to the rectification of the loose pulley. How was it exactly established that the timing was not being "pulled"?

The problem is that all is and has been assumed, based on information which is not absolutely definitive. Furthermore experiments envisaged will not in practice indicate exactly what is transpiring. All is rather hit and miss.

Bill has shown an interesting paper. which indicates that the a knock sensor signal has been used to detect valve operation by analysing the audio signal produced. A special or modified sensor may been involved, we do not know.

I have suggested a means of establishing fact in my post No. 14, which appears to have been ignored.

Well I do agree that the tuning and the problem solving can be hit or miss, depending what is being measured and how the problem is being tackled.

In our case we knew the timing was being pulled from driving Graham's car connected to a data logger at Zen Performance. We did actually fix the offending key while the kit was all on Graham's car, and the timing came good.

It runs even sweeter on my car because we put on a new pulley and a new key on the shaft, knock on wood, pun intended

I'm not in a position to try your amplifier test, my car is in the UK. It looks a good scheme though.

Joe

[sicksubie]

I just bought an intake temp gauge and am about to order a meth kit from snow performance. Using that gauge and running the various combinations on the dyno when I go I should be able to determine pretty accurately the cause of teh timing issue. However if someone has a select monitor I could borrow it would be appreciated.

[svxistentialist]

Originally Posted by sicksubie

I am going to the dyno the Monday after Thanksgiving. I will be renting it for either 1 or 2 hours and will be fooling around with different octanes as well as the two different versions of LAN's software that I have.

Joe,

It is NOT intercooled but a methanol kit is planned for the future to help in the cooling of the intake charge.

I'm planning the same. However, as you are not currently using a charge cooler you need to keep your boost lower for safety.

Just as an example my calculator shows you delivering about 312 hp at 12 lbs boost [I'm assuming a Whipple 1600 here, let me know if your model is different] However at 8.5 CR and no cooler your cylinder temps are going to be way too high at 1211F

When you drop to 9 lbs pulley, you are now making 290 hp, but your in-cylinder temps drop to 1160. Still too high, but safer.

At 6 lbs boost you will be making 267 hp, but your temps drop to a just-about safe 1100F.

And just in case you were wondering, using water/methanol injection you will be making about 375 hp at 12 lbs with a cylinder temp of around 1010F, no more detonation!

Joe