FORGED PISTONS and KNOCK SENSORS
06-25-2009, 09:00 PM
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FORGED PISTONS and KNOCK SENSORS
Just incase you're not aware of it, when rebuilding your engine and going with forged pistons, the knock sensor MUST be moved to the lower boss on the side of the block.
These pistons don't warm up as fast as cast ones do, and they send a harmonic pinging sound to the sensor which in turn sends more fuel, that's not needed. Drill and tap the lowest free boss under/below the sensor and install knock sensor there. BE VERY CAREFUL NOT TO DRILL DEEPER THAN NEEDED!!! Or you'll have a nice hole in the side of the block!! I found no need to drill deeper than what was already there, just a little larger to accomodate the Tap.
Just something to think about when building your engines
HAWK4295
These pistons don't warm up as fast as cast ones do, and they send a harmonic pinging sound to the sensor which in turn sends more fuel, that's not needed. Drill and tap the lowest free boss under/below the sensor and install knock sensor there. BE VERY CAREFUL NOT TO DRILL DEEPER THAN NEEDED!!! Or you'll have a nice hole in the side of the block!! I found no need to drill deeper than what was already there, just a little larger to accomodate the Tap.
Just something to think about when building your engines
HAWK4295
06-26-2009, 02:39 AM
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Here's another new thing to learn:
The knock sensor doesn't send more fuel- when the ECU detects detonation via the knock sensor, the ECU to drops the timing advance out (retards the timing to baseline) in order to prevent detonation. The sudden change in timing produces the same effect as if the engine were to suddenly get more fuel.
Also, forged pistons expand more when heated than cast ones do. This means forged pistons are slightly smaller than cast ones so that they have the same diameter and wrist pin clearance as cast do when warmed up. This looseness when cold causes 'slap' which the knock sensor can detect and if the signal is 'loud' enough, will trigger the ECU's response as if the engine were detonating. This is why moving the knock sensor lower in the block can prevent the problem with the timing changing when it shouldn't. However doing so also prevents the knock sensor from hearing the moderate detonation it should be able to hear.
The knock sensor doesn't send more fuel- when the ECU detects detonation via the knock sensor, the ECU to drops the timing advance out (retards the timing to baseline) in order to prevent detonation. The sudden change in timing produces the same effect as if the engine were to suddenly get more fuel.
Also, forged pistons expand more when heated than cast ones do. This means forged pistons are slightly smaller than cast ones so that they have the same diameter and wrist pin clearance as cast do when warmed up. This looseness when cold causes 'slap' which the knock sensor can detect and if the signal is 'loud' enough, will trigger the ECU's response as if the engine were detonating. This is why moving the knock sensor lower in the block can prevent the problem with the timing changing when it shouldn't. However doing so also prevents the knock sensor from hearing the moderate detonation it should be able to hear.
06-26-2009, 07:24 AM
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Yeah, I was going to say that many knock sensing systems are tuned for a very particular application and that moving the sensor might render it largely ineffective.
06-26-2009, 08:03 PM
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I haven't had any problems.
HAWK4295
06-26-2009, 09:50 PM
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Kay....dodo those YEARS include datalogs and comprehensive testing, or just "I didn't hear anything, so it must be alright"?
Last edited by Dirt Driver; 06-26-2009 at 09:52 PM.
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