Testing Toward MBT — 6400 RPM at 23.5 Degrees

Today’s test is a consideration of if a Cadillac STS-V supercharged VVT DOHC 4.4L V8 will make more power or less power with slightly less timing at 6400 RPM.  I am using Hp Tuners to data log and for one graphic, and Virtual Dyno for the other graphic.

Cadillac’s Max Torque vs RPM vs Timing table suggests that 23.5 degrees of advance is ideal at 6400 RPM, but the PCM commands more.  So we test and see which is more right.

Torque and HP vs Timing

Torque and HP vs Timing

This graphic shows Delivered Torque in blue, Calc Hp in green, and timing in red.  During this run I had also made a small adjustment to 2-3 shift points so that we get closer to redline in 2nd before the shift.

Test: Our focus is on 6000-6700 RPM — does the HP drop off with less timing, or does it stay on an up-slope?  My observation is that it stays on an up-slope.

Virtual Dyno runs

Virtual Dyno runs

I also captured 2 virtual dyno runs, on the same road, same day, same direction.  The first was with the intercooler temps lower, and the 2nd just after the 1st so with intercooler temps higher.  Clearly the results are sensitive to intercooler temps, as well as normal variances in test method, etc.

Although the first run in red slows an early spike that over-shadows the high RPM performance, in neither run does the performance fall off a cliff past 6000 rpm, which is what we are looking for (above 400 whp is a good result in this range).

HpTuners gauge snapshot at peak RPM 2nd gear

HpTuners gauge snapshot at peak RPM 2nd gear

Conclusion

The reduction in timing to 23.5 degrees appears to make power similar to the higher timing point — no disadvantage from 6000-6600 RPM.  We want to run the least timing that produces equivalent power, so this seems a good result.

The slight adjustment in 2-3 shift points was successful at getting better high-rpm data in 2nd for testing.

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