Cadillac XLR LH2 V8 Tuning – More Tune 9a

Tonight I had cooler weather so I re-tested Tune 9a for baseline comparison.

XLR Tune 9A2 Comparison Calc HP

The 9A2 runs showed some KR spikes at 4150 rpm and 5000 RPM. This appears to relate to a high IAT advance multiplier at those RPMs, which I will zero out for Tune 9B.

XLR Tune 9a2 to 9a comparison

The Virtual Dyno for 9a2 was equivalent to 9a1, which is good news (same tune, different day).

Tune 9B will also reapply the MAF 2% touch up around 8,000 hz since there are some signs of running lean there.

XLR Tune 9A2-0139 HPTuners

The issue of KR due to multiplied IAT advance at lower temps could be why the XLR has consistently run better at high temps (which is counter-intuitive). In the next tune I will change the multipliers below 6000 RPM/below 104F for IAT advance to 0. The alternative would be to zero out IAT advance adders at cooler temps, but there may be some value in keeping them at higher RPMs.

Because the KR doesn’t go up at higher RPM it may be false knock?

Cadillac XLR LH2 V8 Tuning – Tune 9A OEM VVT plus less adv high

Tune 9A goes back to OEM VVT Tuning, and pulls 2 degrees of advance near redline where combined timing was above MBT.  Timing elsewhere was returned to OEM. KR attack and decay were modified.  Unfortunately for comparison today’s test was much warmer than yesterday’s test conditions.

XLR Tune 9A-0304 comparison to 8A calc hp

Even corrected the hotter weather today drove ~2 degrees of IAT and ETC delta timing.  Ignoring that difference however, restoring VVT appears to have restored the torque dip at 4800, and looks better above 6400.  Tune 9A ‘solved’ the KR issue as well, which perhaps was coincident with the VVT changes?

XLR Tune 9a-0304 Vdyno Comparison with 8A-0942

Virtual dyno was equivalent between 9A and 8A, although 9A has a lot less timing.  This seems consistent with the delivered torque/hp corrected.

Next I would like to see some 9A data under the same conditions as 8A.


Cadillac XLR LH2 V8 Tuning – Tune 8A

Tune 8A commands 12.8:1 AFR from 1500-6700, where Tune 7A was at 12.5:1 AFR.  The VVT in 8A has some minor cleanup in an unused area.   The piston protection in 8A is at 8192; in 7A 6400 rpm.   7A was the ‘just advance the timing’ run, so 8A has 2 degrees less timing from 2300-5600 more or less, with -3 at 4200-4400.

XLR Tune 8A all 5 runs calc

I ran 5 runs today to study run to run variance.  I have started not initiating the scan until ready to test, which avoided (randomly?) the scanner hang issue. The reference number for each test is the Tune (8A), the time the run starts in its scan (0942) and the test area used for the run (A, B, C).  Test area A data was uniformly hard to smooth for Virtual Dyno, so I will plan to exclude it and focus on B or C.

The runs on the graph above are all the same tune 8A.

XLR Tune 8a to 7a calc hp comparison

This comparison of 7A, which was non-viable due to heavy KR, vs 8A-0942C.  Even with the main spark retard in 8A there is still some KR in that run, perhaps caused by IAT advance?

XLR Tune 8A comparison timing to 7A

8A is able to run more timing than 7A partially due to conditions, and due to avoiding some KR at 5000 RPM.  The max timing on 8A actually runs above MBT so I will reduce timing from 6500 RPM. One knock event causes 3 degrees of KR and the characteristic stair-step decay from 4250-5500 rpm.  My goal is to tune out any knock.

These show the raw calculated data, with no smoothing.  All 5 runs HP data, 1 run torque data for reference.  The hp/torque maximums are shown for each run, which is less valuable unsmoothed but provides a reference.

XLR 8A-0942C Virtual Dyno

This is the Virtual Dyno wheel hp / torque for the 8A-0942C.

Here is a comparison across viable runs with a Tune 7A run included

XLR Tune 8A 3 Viable Run Comparison

Given 7A and 8A are on different days they appear to be equivalent and I don’t see a tune delta in the Virtual Dyno plot.

XLR Tune 8A comparison 7a Virtual Dyno