Category Archives: Test Info

Cadillac XLR Tune 3 MAF Tuning & Tune 4

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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.

XLR Tune3MAF to Tune4

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).

XLR Tune4 1020

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

XLR Tune4B2 compare Tune4 and Tune3

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.

XLR Tune4b vs Tune3 hptuners

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.

Cadillac XLR Volant Intake baselines

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XLR Tune3 Volant2 vs Volant1

Today’s test was a repeat for baseline of the Tune3 with Volant air intake.  Today’s test in Red, previous test in blue.  What we see is that the two results are close, although the blue run has a late peak I would like to repeat more often.

xlr tune3 volant 2

At 6626 rpm today’s run was at 25.5 advance, AFR commanded 12, 192 ECT, -1.0 IAT Adv.

xlr tune3 volant 1

Previous run at 6625 RPM was at 25.0 advance, AFR commanded 12 with 203 ECT, -1.1 IAT adv.

The engine torque calculation guessed today’s run was making more power (297 vs 290), but the Virtual Dyno showed the reverse.

I think it is important to capture this type of data to calibrate the test.  The two lines do ‘snake’ together a bit and graphically are equivalent if one ignores the difference in peak values.  I plan to collect more baseline data then move on to Tune4.

Cadillac XLR Volant Cold Air Intake Install and Test

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Today I installed and tested a Volant Cold Air Intake p/n 25846150 for the Cadillac XLR.

Install

The install is pretty easy.  A screwdriver is needed for the clamps, and a bit of WD40 or similar for the hose fittings.

IMG_2646

This is the intake setup on the stock XLR.  The air comes into the middle then flows down through openings facing the middle to dual filters and back to the middle and through the MAF into the intake.  There are resonance tubes along the way to quiet the intake.

IMG_2648

So the engine has to breath through that opening just above the filter on the left, then down through the filters 90 degrees, 90 degrees back to the center, where they turn 90 degrees to get to the MAF.  Good filter area.  The twists and turns the air takes are to prevent hydrolock in a heavy rain?

IMG_2653

Stock intake vs the Volant Intake.  The Volant has cones and large tubes for flow vs the elliptical pinched approach the OEM took.

IMG_2656

Behind the MAF was this resonator tube.  This probably captures and eliminates certain intake frequencies?

IMG_2658

The XLR MAF is a switchblade style, and has a MAF screen to smooth air flow.  I left that in place, but removed the resonator setup and air now flows directly from the MAF to the throttle.

IMG_2659

This shows the Volant in position.  The hose to the right is not attached yet, but goes from the breather hose to the intake.  It took a bit of muscle and a drop of wd40 to get the hose barb properly inserted on the engine end.

IMG_2662

Close-up on hose attachment and placement.

IMG_2665

One of the two Volant cone filters up close.

IMG_2667

The blue filter matches the blue XLR.  The hood closed fine.

IMG_2668

No trouble lights.

Results?

I have been using Virtual Dyno to measure results.  These are 2nd gear pulls so they vary from a chassis dyno which would be done in the gear closest to 1:1 which for the XLR is 3 or 4.

XLR Volant First Test 236 whp 224 lbft baro corr

[click to zoom in, back to return]

This graph shows tonight’s run in Blue, and the prior run with current tune in Red.  The runs are on different days.  Today was hotter at 95F vs 88F yesterday.  What this appears to show is that the Volant added 10 whp and 3 lbft of torque.  The blue line is clearly above the red line from around 4700 RPM up.  This would mean the 320 hp LH2 now puts out about 320 + 10/.8 = 332 hp at the crank.

The intake also had an effect on the intake sound, and the exhaust sound.  The fuel trims kicked up to around 10% each, which is another indication the MAF is now getting more air in than it expected.  I will want to adjust for that in the tune or have the MAF dialed in on a dyno.

The XLR did not show any trouble lights, and the idle is smooth as always.   The calculated hp and torque were lower than expected, so that seems to suggest that these are not predictive of real-world performance?