Tuning VVT — Establishing a Baseline

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Variable valve timing allows tuning of the camshaft timing across the RPM range.  In my 2008 Cadillac STS-V, the DOHC engine allows individual tuning for exhaust and intake cams.

TUTD3 baseline hp torque vs boost sc vac

This graph shows today’s run delivered torque and calc hp vs supercharger boost and supercharger inlet vacuum in psi.  It is provided as a baseline comparison for how the engine performed today.

tutd 3 hptuners peak

Hptuners capture at peak in 2nd gear.  This run shifted in custom TUTD mode at top of 2nd to allow selection of 2nd gear but smooth transition to 3rd.

TUTD3 KR vs total KR

I have previously been charting KR, or knock retard.  I added tracking for Total KR, which includes burst, or pre-emptive knock retard.  The KR is shown in yellow, and the Total KR in green on this chart.  I think you can see the Total KR anticipate and over-shadow the KR, as well as the fact that the Total KR runs a degree of KR all the time, which was a surprise to me.  More thought and study needed here.

I also should note that my gauge for KR tracks the Timing Retard sensor, which seems to be different from just KR or Total KR.  Again, more study.

TUTD3 cam position

Finally, this graphic shows the VVT operation — the gold line is the intake cam position, and the green line is the exhaust cam position.  Basically, in the pressure range the V is running, the intake cam is commanded to 20 degrees, while the exhaust cam goes from 5 degrees at low RPM to 2 degrees midrange to 4 degrees at high RPM.

In our previous experiment, I changed the exhaust cam to show a more expected pattern similar to lower pressure settings by adding 1 degree at 4800 and 2 degrees of cam position from 5200 on.  We did not see a improvement or degradation, so it was reset it to OEM for this run.

It surprises me that the VVT cam position is not constant (waivers).  I am not sure if this is an effect of the variance in the boost, or if this is a cause of the variance in the boost.

TUTD3 2013-06-22 low virtual dyno result

I included a Virtual Dyno run.  Other than it is hotter now I am unclear why this run was markedly lower than prior.  Both are ‘cold’ runs at operating temp but without heat soak.  The MAF also shows less air in lb/min so I don’t think it is just test variance, but I am uncertain what caused.

TUTD3 RPM vs Time comparison

This graphic shows the raw data that Virtual Dyno uses — time deltas and RPM for the two runs shown.   The runs appear equivalent until 6300+ rpm, where today’s run tapers off.  This may be an effect of the TUTD shift for today’s run vs the hold to redline of previous run?

I will note that I got gas from an unusual location on last trip, not my normal source, but was marketed as 93 octane.

The boost psi looks similar between the two.  The good news is programming the TUTD to shift automatically avoids pulling the V back in to normal then back to sport, which appears to have been causing the RPM pattern that disrupted the virtual dyno readings.  The last few charts have not shown that issue.

 Summary

The purpose of today’s test was to select and record VVT cam positions over RPM to characterize current state with OEM tune.  Next I plan to study changes to the intake cam position.

Testing VVT Exhaust cam retard at high RPM

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Today’s test was not a normal test.  First, I was dispatched for a breakfast run to Starbucks, which adds intercooler heat.  Second, the highway was jam packed with some problem, and the run was captured in an alternate location.  All that noted, I feel we can reach some conclusions.

TUTD 2013-06-21 exhaust cam test

This chart shows exhaust cam position for the VVT timing.  The cells in red are our test settings — adding 1 degree of retard at 4800 rpm, and 2 degrees of retard from 5200-6800.  What we hope to see is a change in the slope of the HP and Torque curves as a result.

tutd 2 2013-06-21 add exhaust cam retard

This chart shows today’s hotter run vs previous cooler run.   I am not focused on the absolute values so much as the slopes for today’s study.  Here is a zoom in from 5800-6600:

TUTD 2 2013-06-21 zoom in to study slope

What this appears to show is that the change in the exhaust cam timing didn’t cause a huge improvement or loss in power and torque at 4800-6800.  However, the slow of the blue torque curves appears to suggest that the addition is overall not an improvement, since the current curve decreases over time in this range at a faster rate than the previous.

The TUTD shift point did work correctly for this test, so that change will help with future testing.

TUTD 2 2013-06-21 exhaust cam retard

Next I will restore the exhaust cam VVT timing, and test an adjustment of the intake cam vvt timing.

TUTD shift speed test 1 — Too high

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Tested my 2008 Cadillac STS-V with the LC3 Supercharged 4.4L DOHC VVT V8 this morning cold, low on fuel.  Today’s experiment was to add an auto-shift at the top of the tap-up/tap-down shift for 2-3, so I can lock the transmission into 2nd gear for testing, but then have it auto-shift at redline and avoid either having to pop it out of sport mode and back in to get it to auto-shift, or just hitting the rev limiter in 2nd.

For this test I also restored the stock calibration higher advance at high RPMs.  I recognized that what this higher advance does is offset the beginning of IAT2 retard, with the net effect of hitting closer to the ‘ideal’ timing.

TUTD Shift Speed miss 2013-06-20 hptuners

Unfortunately, it never shifted and just hit the rev limiter in 2nd.  I will have to recheck the calibration for commanded shift speed and rethink why it didn’t shift.

TUTD shift speed miss 2013-06-20

Max boost of 9.5-10 psi, and a nice max delivered torque of 468 lb -ft at 3530 RPM, max calc hp of 548.8 hp at 6580 RPM.

TUTD shift speed miss 2013-06-20 VD

The Virtual Dyno shows a steady 377 WHP from 5500 on — looking a lot like the car needs more something to keep raising torque/hp after 5500 RPM.  I would like to see the car get to 440 WHP in 2nd gear tests like this one (!)

Conclusion:

Today’s test was not successful in changing TUTD shift behavior.  The car put up good numbers, although the Virtual Dyno WHP continues to stay below goal.  Restoring the additional timing at high RPM seem successful.  I have recalibrated the TUTD for the next test.

Update:

TUTD timing vs retard b

Pulled 0.5 of timing at the two points where KR is coming up, and added some timing at 6800 RPM to push up the last bit of the curve.