Hi guys, I am scratching my head at why my L67 car is knocking so damn much and I'm having to pull so much timing. Its not a stock car, and I'll briefly list the mods I've done just for reference.
- CAI
- 180 TStat
- Autolite Copper 103 plugs
- 3.4" SC Pulley
- ZZP Headers and 3" downpipe
- Custom 2.5" exhaust
- 1.9:1 Rockers
- Northstar throttle body
- Ported supercharger blower housing
Talking with some guys on 3800 forums, most people run high teens in their WOT timing for cars with similar mods, yet I am barely able to get above 10 degrees, not to mention a couple cells requiring as low as 2-3 degrees to be knock free. Some things I have done and crossed out are
- Replaced louvered core resonator with a Vibrant perforated core one
- Compression test (Passed fine)
- Cut out and installed a new high flow cat
- Ran 1 and a half tanks of injector cleaner
- Dropped another step colder plugs from Copper 104s to 103s
After doing all that I maybe gained 2 degrees of timing max, I am still around 10-11 degrees WOT. Using TrackAddict, I am barely below 15s in the quarter, which the car has run bone stock years ago, so something is clearly up and it is not making nearly the power it should be (IIRC with these mods it should roughly be high 13s low 14s).
What else can I check/try here? Am I doing something horribly wrong with my tune that's causing it? Or is this most likely something with the engine? Its got 170k miles on it, could I have an injector getting bad and leaning out one cylinder? I attached my most recent scan and tune, I'll also put a screenshot of my table before I did some smoothing to see just how much I had to subtract out of it from the scan.
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Copper drive 3.hpl
Copper drive 3.hpt