: Answering ? on sensitivity of knock sensors and tuning..



kencav
07-11-09, 11:42 PM
Luna- Jesse would be the best one to explain this but I will give it a go. This all started when my installer who is also an exellent tuner looked analytically at Jesse's tune we were uploading and expressed concerns that knock sensors built into the ECU were being "desensitized" and that this might not be a good idea. He related this to me and I asked him to give Jesse a ring

It ends up, you don't mess with the Zohan aka Jesse!

Seems that Jesse knows these factory calibrations and the reasons they are set the way they are- theres a shocker. Our knock sensors are actually 16-18 percent OVERLY SENSITIVE from the factory. Therefore they will pull timing and hence engine performance much quicker then if the were at a neutral setting. Jesse knows this and that is why he is smarter than the average tuner when it comes to the 2009 CTS-V

I also found an interesting little quip off the internet

Most modern engine management systems incorporate a knock sensor or two (LTIs use one on each side of the block) for closed loop timing control. These systems only have a limited amount of control and are designed to stop detonation in the normal operating range of the engine, not to compensate for 12 lbs. of boost on a 95 day. The sensor itself is a piezo-electric accelerometer, or a sort of an electronic tuning fork. It's tuned to create an output voltage and is designed to bore and chamber geometries. When a given frequency of knock is detected, it in turn sends a signal back to the ECU identifying detonation, and the ECU retards timing


Tuning A Knock Sensor Equipped Engine
When trying to get maximum drag strip performance out of a feed-back timing control engine, you might want to disconnect the knock sensor. The sensor is designed to listen for vibration, and it does a very good job. Anything that can cause a harmonic might be picked up by the sensor and be interpreted as detonation. The major problem with that lies in what is called the hysteresis of knock. Once knock starts, you need to pull out more timing than would originally be needed for knock to ever occur. For example, if your Z28 makes maximum torque and doesn't detonate at 38 advance and you advance the timing to 39 and detonation occurs, the knock sensor may have to pull the timing out to 30 to stop the knock. There goes the timing and there goes your ET and mph. Also, at WOT the engine might knock, just for a millisecond, and bingo, there goes the timing. If you have an exhaust that shifts slightly during hard acceleration and vibrates, say goodbye to advance again.

The cure is to run good unleaded fuel; around 100 octane works best with today's performance cars. And you should also turn off or decrease knock sensor sensitivity

End of quip

Of course we still will detect knock with Jesses tune and prevent detonation- but we will also obtain better performance by desenstizing these overly sensitized knock sensors

Hope this helps LUNA

Jesse I need you as a lifeline here!

backup
07-12-09, 11:04 PM
Thanks for the info. How fast does it advance the timing after detecting knock? Is it a few seconds, a few minutes, or longer? Let's say you get a tank of bad gas, and knock occurs and is detected thru the whole tank. You run it near empty and refill with high quality high octane, but the ECM already has timing backed off, how long before it advances it forward with the good gas?

Luna.
07-12-09, 11:26 PM
Thanks for your thoughts Kencav; very interesting.

Knock, especially on a blown motor, isn't a good thing. Makes me wonder, for GM made them overly sensitive for a reason. If it's for something dubious, like smog, I'd gladly bomb the heck out of them. If it's so the motor doesn't go kaput...that makes me a little more nervous.

How do you feel about de-sensitizing them?

kencav
07-13-09, 12:21 AM
To answer both ?- a am no expert on this- i would enlist Jesses help here- but Jesses entire tuning philosophy seems to be

1- there is alot left on the table with these FI engines for us to exploit and

2- he does not take shortcuts like shutting off o2 sensors to eliminating problems

3- He would not overly desenitize something if it would cause harm to our engines ImHO

A GOOD QUESTON THOUGH IS- if bad gas increases knock sensitivity do "oversensitized sensors" help buffer for that?

Thoughts Jess?

Mazz
07-13-09, 03:10 AM
smart Q

this is interesting

Gotham CTS-V
07-13-09, 09:34 AM
Thanks for your thoughts Kencav; very interesting.

Knock, especially on a blown motor, isn't a good thing. Makes me wonder, for GM made them overly sensitive for a reason. If it's for something dubious, like smog, I'd gladly bomb the heck out of them. If it's so the motor doesn't go kaput...that makes me a little more nervous.

How do you feel about de-sensitizing them?

GM made a 4200lbs sedan that laps the Nurburgring in under 8 minutes, blazes down the 1/4 mile in 12 seconds, and can top out at almost 200mph. They gave us a 5 year warranty. I bet they felt the performance was definitely enough to dominate the segment while still giving us the 5 year warranty. Any more power and they may not have felt comfortable giving such a warranty. I'm sure someone like Jesse will give more info though, but that just seems to make sense to me. :thumbsup:

kencav
07-13-09, 10:42 AM
GM made a 4200lbs sedan that laps the Nurburgring in under 8 minutes, blazes down the 1/4 mile in 12 seconds, and can top out at almost 200mph. They gave us a 5 year warranty. I bet they felt the performance was definitely enough to dominate the segment while still giving us the 5 year warranty. Any more power and they may not have felt comfortable giving such a warranty. I'm sure someone like Jesse will give more info though, but that just seems to make sense to me. :thumbsup:

Stallion, or was that scallion (couldn't resist the Apollo Creed line from Rocky)

I would say to each his own. Some of us enjoy modding, and are prepared to take the risk associated with it. I think you better have your other financial priorities in order before embarking on journey's like this. That is also why a am rolling with Jesse and his experience here

And as far as dominating the segment- right now yes but things change fast

Gotham CTS-V
07-13-09, 02:14 PM
Stallion, or was that scallion (couldn't resist the Apollo Creed line from Rocky)

I would say to each his own. Some of us enjoy modding, and are prepared to take the risk associated with it. I think you better have your other financial priorities in order before embarking on journey's like this. That is also why a am rolling with Jesse and his experience here

And as far as dominating the segment- right now yes but things change fast

I totally agree brother. I enjoy modding and have plans to mod this car as well. I spoke with Jesse over the phone about it last week but am still waiting for him to email me a quote on the parts and a list of what I would need...I guess he is on vacation?