Exhaust, Otr, Dyno and some noise :-(

[ZB_Driver]

I think it is slight knock in Open Loop under peak load, evidence that changing induction and exhaust pressures mean recalibration.
In Sydney Oztrack and AutoWerks are great for this sort of tune.

I know this is an old thread but I thought I would share some knowledge as I am curious to know what you did to fix the issue.....

Without seeing the engine data I would agree with that engine knock as the root cause for the noise. But why is it knocking though....

As someone who has done factory engine calibrations for GM on LS3's (not "dodgy" aftermarket tunes ) the likely reason for the engine knock is either:
1. the spark table(s) has been changed from factory settings, i.e. too advanced, but this will be brief knocking as the knock sensor should detect this and retard the spark temporarily and hopefully adjust short term spark adaptions (called octane scalars) unless the tuner has disabled them
2. aftermarket tune has changed knock sensor calibration (some tuners turn it off completely and tell you drive 98RON only, which is very dangerous to the engine, especially on a hot day with high intake air temps as it needs more retarded spark under those conditions)
3. since it is likely the peak airflow is higher at this RPM than factory tune due to the hardware mods, you may have fallen off the edge of the factory spark map (it is a map of RPM and Air Per Cylinder which is a measure of airflow) which means the spark is clipped at too high a value as it corresponds to a lower APC than you are actually operating. FYI, as a general rule the higher the airflow, the more retarded the spark needs to be (all other things being equal, i.e. fueling, coolant temp, intake air temp etc which also influence knock tendency).

 

[Emco]

Not sure about the noise, Sams performance done my tune and very happy with results

 

[RevNev]

See those idiots who say you don't need a tune and the computer will adjust, are talking about fuel trims under typical conditions - Closed Loop. Yes there is some scope (+/-20%-30% trims) to get fuelling right in Closed Loop but when the ECU switches to Open Loop the calibrated values are preset, and are definitely incorrect for the change in induction and exhaust pressures.
Tuning the Malfunction Indicator Light off for a Diagnostic Trouble Code relating to improper value reported from rear Heated O2 Sensor does not affect the tune, unfortunately, no.
If you drive like a granny (as it appears most people are fine with by just turning off the MIL for the DTC caused by the HO2S value), then probably fine. But the engine is way out of optimal tune, potentially destructive and drives worse.

The air fuel ratio is massively rich in open loop mid to full throttle with minimal ignition timing and they're still too rich with minimal ignition timing with an OTR, 1 7/8 primaries, catless and twin 3" exhaust. Other than adding a supercharger, nothing bolt on will lean the engine out or cause ignition timing to advance to the point of engine damage with a stock tune. Making power with a custom tune is primarily advancing ignition timing and leaning air fuel ratio out to maximise engine efficiency.

The engine light with high flow cats or catless, is a catalyst efficiency code that needs to be switched off. The rear O2 sensors will only throw malfunction lights if they're not working properly, nothing to do with cats although there's no tuning purpose for them.

 

[RevNev]

If you are not getting a tune then no need to do CAI in any form (including OTR) unless you want the noise. If getting a tune then yeah tune to CAI and headers.

HSV got 340kw with an improved CAI , headers and exhaust with same tune up as a stock 304kw LS3 SS. A better CAI or OTR increases power by leaning out an overly rich air fuel ratio a bit. A CAI, headers and exhaust on a stock LS3 and stock tune will at least match a 340 R8 and likely make more power in most cases.

 

[moveage]

HSV got 340kw with an improved CAI , headers and exhaust with same tune up as a stock 304kw LS3 SS. A better CAI or OTR increases power by leaning out an overly rich air fuel ratio a bit. A CAI, headers and exhaust on a stock LS3 and stock tune will at least match a 340 R8 and likely make more power in most cases.

Yes with a retune or another tune CAI provides more air mass, cooler intake air temperature to allow more greater margin against knock.