I've just changed to a straight thru muffler and noticed that my SAFC2 shows a higher knock count !!!

Any idea why is this so ?

 

More boost due to less backpressure?

 

But even at idle and non-boost condition, I noticed knocks which I did not encountered previously ! Strange !

 

Did you also add a downpipe? I've heard that some downpipes will cause false knocks to be detected from rattling against the crossbraces.

Even if not, maybe your exhaust itself is rattling?

 

Nothing is changed except the muffler itself ...

A rattle at the muffler should "not" transmit all the way back to the engine block and knock sensor right ? (I assume the distance is too "far" away)

 

I would assume the same (too far to trasmit back to the block). Sorry, I'm not familiar with the SAFC2. It'd be nice to know what the 'real' knock count is in the ECU. (I mean, doesn't the SAFC2 just tell you the knock sensor voltage?) Do you have a Tactrix cable/EvoScan?

Maybe you coincidentally got a bad tank of gas?

Maybe if you dump some race fuel in it, you can see if it goes away. If it doesn't, you know it's probably something noise related.

 

Thanks ... I've tone down my SAFC settings to compensate for the higher knock count.

However, like usual, the car felt more powerful, and i doubt the ECU is retarding ignition timing due to the higher knock count.

Despite all the rumors about inaccurate knock count on SAFC2, I am still concern with a sudden increase in knocks.

Maybe I should just pop down to ensure nothing is moving and rattling.

OH, btw, it only shows higher knock after the car is well warmed up and running .. not when it's cold

 

It's not rumors

SAFC2 measures knock using voltage, so depending on how that voltage is measured, it translates to false readings if the following is true

bad ground from ECU
bad ground from SAFC2
bad ground from chassis to battery
loose connection from SAFC2

Meaning it's as accurate as using the narrowband O2 sensor to determine how rich or lean you're running ..

lastly, YES rattles ANYWHERE that's attached to engine may get transmitted through the engine to the pickup inductor (which basically is just a microphone for noise)

 

Yeah, but strangely, when I set the SAFC settings to 0, the knock on SAFC2 shows 0 most of the time ...

So must be the engine behaving differently right ?

 

The SAFC is useless for reading knock as it doesn't know what the noise floor is supposed to be. Also it is HIGHLY unlikely that you are getting knock at idle.