It's amazing how often you turn out to be the "exception" ...
Richard
Extraordinary claims require extraordinary evidence.
Richard
This was a minor amount of knock retard compared to what it would do at times on 87 octane and the stock tune with the factory 195°F thermostat and factory 5 bladed fly swatter fan blade. It still jumped up around 3° knock retard when the transmission shifted into 2nd gear. I think this was with headers, small cam but stock compression ratio. Cam really did not change its tendency to detonate as the 9.4:1 compression ratio, detonation prone GM dished piston design and thick OEM head gaskets that kill quench were all still in place. Also this had to be when I was playing with trying to get it to run well on 87 given that it is maxed out at 25-26° of timing. Vortec heads typically make peak power between 29° and 34° BTDC. I could get it to stop detonating but it was a dog with the timing pulled. I put 91+ octane in the tank, cranked the timing up and it ran much better. On 91 octane with a coolant temp of 176-182°F I ran 29° at 4,800 and 32° at 5,600 in the timing map. Shifting at 5,100 had me about 31° and 5,500 about 32°. On E85 that same setup liked 34° of timing and all of that at 2,400 rpm. Torque was way up, 330 @ 2,700 vs 310 @ 3,100 and peak hp went from 257 at 4,900 to 272 @ 4,700. At around 1,500 rpm E85 and the high timing gave as much as a 35 ft/lbs gain, it absolutely loved the higher octane and full timing advance at low rpm. My E85 timing table had as much as 8-10° added in places.
The waviness in the maf airflow reading also points to this being before I upgraded the valve springs. I was getting valve float so severely before I changed the springs that it lost 30 hp at the wheels between 5,150 rpm and 5,350 rpm. Post springs the power leveled out and it would rev cleanly to 5,500 and stay within 10hp of the peak at 4,900.
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