Today’s road test is a repeat of the previous test to add to the baseline for Tune 5.  The only change from previous was to decrease the TUTD shift speed by 1 mph to 81, and to change the PE ramp from 0.1 to 1.0 (range 0.01 to 2).  This value effects how quickly the engine attempts to reach the PE fueling value.  Since the commanded air fuel ratio is now set constant from low RPM to high, we would expect this to have impact only just after wide open throttle is reached.

Today’s run is in Blue, and we are comparing to the Tune 5 run in red.  What I see is the runs are very close.  Today’s somewhat better torque may be an (additional) effect of cooler air, or it may be helped by the PE ramp up.  We’ll see how other runs look — certainly I don’t see any disadvantage from the higher PE ramp.

The calculated HP peak was at 6554 RPM.  ECT 194F, ambient 88F, Intake air 90F, MAT 115F.  Some IAT retard.  Peak advance ~26.5 degrees.

Madtuner.com offers a tune for the LH2; they did work on a 2005 STS in 2012 and showed this dyno chart for before / after:

This looks very similar to what I am seeing with the LH2 in my XLR.  They had some glitch in the base tune, but I am looking at the shape of the before & after curves — the HP peaks at 5400 or so and is flat until 6000.  They stop the scan at 6000 rpm for some reason — I suppose because the engine wasn’t making more power past that.  They don’t mention the specifics of their tune.

Cadillac XLR 320 hp picks up 12 whp with Magnaflow catback

The Magnaflow performance exhaust for the Cadillac XLR shows a similar shape in the before and after — HP peaking near 5400 RPM and dropping to past 6000 rpm.

320 hp LH2 Rear-wheel Drive Variant

GM powertrain showed the LH2 continuing to improve hp until 6400 rpm.  Redline is at 6700 rpm.  Note that the GM plot is an engine dyno, and the Madtuners and Virtual Dyno plots are hp at the rear wheels, so we expect them to be different due to drivetrain, friction,  and aero losses.  The part I am considering is the shape of the curve — the engine dyno showed that the LH2 makes a bit more power from 5500-6400 RPM.  To be fair, it is not on the same up-slope as 1000-5500 RPM.

Today’s test added to the Tune 5 baseline.  The Madtuner result is supportive that there is more to be gained here somewhere.  The Madtuner experience closely mirrors my results and varies from the engine dyno.  More testing to follow.

If you have ideas, suggestions, encouragement, or advice please hit Reply!

There are several things you don’t want to have happen when you are tuning a car:

• Tuning laptop crash
• Communication / connection / gadget problems
• Unintended tune changes
• Changing conditions

I think I saw them all today, but here is what I think I learned.

First, I worked on MAF tuning.  With the recent addition of the Volant intake, my long term fuel trims were up 8-12%.  The MAF is tuned for the factory intake, so presenting it with a different air flow is not surprising that it would need some instruction.  In order to tune the MAF I compared long term fuel trims and short term fuel trims with the MAF signal, and used the fuel trim results to adjust the MAF signal in HPtuners.  This calibrates the MAF so that it correctly measures the incoming air with the Volant intake.  now my long term fuel trims are closer to +-5%.  I will keep collecting more data and trim them in.

That produced the RED line – Tune3MAF+Volant.  I was disappointed with this lower HP — the prior baseline runs were 231-236 whp.  I was predicting that tuning the MAF would pull the actual AFR (Air fuel ratio) back to commanded, and that the prior runs were slightly too lean for max power.  So I expected to see today’s test several whp above prior tests, but that was not the result I got.

Certainly it is hot here, and I had the XLR out all day and in the sun, and that effects the tests, but I am not certain yet why the tuned MAF version was not better.

I started a new Tune4, which takes our 50% of the IAT retard at 212F, and 50% of the ECT retard at 212F.  It also turns the engine fans up sooner to try to keep the ECT lower.  I like to have the TUTD (touch up touch down) transmission shift itself at redline, so I modified the transmission programming to have it do that.

This transmission programming caused a bit of a testing issue, as the default is not to shift at redline and so my next test didn’t get to 6700 rpm.  The blue line in the graph doesn’t rev fully to redline.   I have moved the shift up 2 mph further to improve the RPM span for the next update.

The Tune4 line in BLUE also has 2 degrees of advance except where there was some knock retard, and reductions in timing there.  The next update will have a few more reductions around knock — basically by reducing the IAT and ECT retards, and increasing the base spark, I am near the knock limit at mid-RPM (4500-5200).

Tune4 looks promising overall.  I hope to get a cold/cold test in tomorrow morning early, which may tell more about the ‘range’ of our current baseline.  With a bit more touch up this will complete air and fueling, and after more baselines I would like to do some VVT tests.

Update:  Next morning cool air test

In this graph the green line is 9/5 AM in cooler air, with XLR not heat soaked.  Again, I expected this to be higher than the blue result but it was not.  I conclude from this that heat effect is not what is causing the lower than expected result.

Hptuners scan at calculated hp peak.  Note IAT is at ambient, and MAT is all the way down at 112F, with ECT at 189F.

UPDATE after Tune 6D:

I have re-visited all of my tune logs, and I suspect that the adjustments to the MAF were good outside of WOT, but not in the WOT range.  I have extrapolated from the pre-WOT range to correct the WOT range of frequencies.  This would have effected everything from Tune 4 (right after Volant install) to now.