Pre-Ignition / Knock...

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7milesout

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Guys,

On our old school engines, is there any scientific way to determine knock? I have an AFR gauge and it has opened my eyes to what is going in with the carburetion. I have the car tuned as good as it’s going to be tuned, unless I make my own metering rods.

I’m wondering if there is a scientific way to detect knock. It would be awesome just to have a red light that would flash when a knock sensor notices knock. A person could advance timing until they started see some red blinking / flashing. And then back off the timing until it clears away. That would be friggin awesome.

I’m assuming that doesn’t exist. So, what is the next best thing?
 
old school ears......it's not just total timing, the curve has a lot to do with say, my 318 knocking, (you didn't say what motor). even on new cars the sensor can be out of wack if it's torqued too tight or too loose
 
The big 3 have had knock sensors on there engines for over 15 yrs. Where ya been hiding?
 
The reviews on that G4 unit are not that good, and there are other units out there that do the same but are more accurate from what I have seen.
The margin of error in the sensor ECU is too high for some.

I see people selling the G4 unit on ebay with some close to $500 when you can get it for 190 or so elsewhere.
 
If you are hearing the engine ping/knock, you are already hurting it..
 
Advancing timing to just before ping/knock is not always netting best power.
A knock-sensor should be seen as a safety-device to not hurt the engine.
 
Your logic is good, and thinking is smart.
There are other methods of determining engine performance, and detonation kills performance.

I started with a DynoRad, and a dash-mounted,dial-back, timing box.
The DynoRad is an accelerometer in a tach-like housing. You input yur weight and hit the gas and when yur done it has logged your distance to time, converted it to power, and amassed it into a sequential list for you to transfer to graph-paper. Then you make a change to the tune and run it again. And build yur new curve. Compare better or worse, and make a new plan.
The G-techPro does a similar job and you don't have to do the graphing.
The instant you lose power, you gotta ask "what happened?"
Yur butt-dyno will not tell the difference of 2 or 3 degrees short of optimum, but the engine will sure complain about 1 degree too much. Point is; sneak up on it.
 
BigBlockMopar said:
Advancing timing to just before ping/knock is not always netting best power.
A knock-sensor should be seen as a safety-device to not hurt the engine.
Click to expand...
Hey, that's a really good point. And I'm agreeing with you.

Thanks for the link to the Knocklink. I didn't know it existed. Not that I'm going to rush out and buy it. But something like that, that actually works would be great, if not necessarily for max power tuning, but to at least let me know I may be getting knock that the ears are not hearing.

I have a 72 Scamp, with about a 75 LA 360. Mild mods, well tuned carb. I don't hear any knock and it runs great and fires up reaonalbly well. I know knock sensors have been around a long time but didn't know if there were anyway to adapt them to our vehicles.

I'm considering nitrous on the ole Scamp. Just for giggles. With the AFR gauge I should be able to tune it to perfection ... and safe. The timing retard with nitrous makes me want to ensure the engine is not detonating prematurely. That's what started my thinking about this.

It would also be nice to know exactly how much misfire the engine is experiencing, and at what rpm. My guess is that on my engine it misfires little to none once above 1,500 rpm or so. But at idle, it may be happening a lot. I would like to mess with the idle speed and idle AFR to reduce misfire as much as possible ... if I could be seeing scientifically what exactly is going on.


7milesout
 
If you do a Google search there are a number of people who've adapted factory knock sensors. It turns out they are mostly an audio transducer, that is, a microphone. Some guys actually ran them through a small amplifier and headphones!!
 
OEM knock sensors operate at a specific frequency range, and specific location depending on engine. The knock detection is windowed in time to observe around ignition event, rejecting other unrelated engine noises.
 
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