Category Archives: HP Tuners

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 Northstar LH2 4.6L V8 VVT Tuning #hptuners #Motorama

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The LH2 V8 added variable valve timing (VVT) based on the Premium V6 schema of the same time.  Interestingly, the LH2 and the LC3 use the same base cam timing, which reinforces how much the LC3 Supercharged V8 in my STS-V is a supercharged 4.4L LH2.  It may also give us some insights into how the LH2 VVT is programmed vs the LC3 VVT.

Here in Plano, Texas we stay in the High BARO table, so we’ll be looking there.  The same principles should apply in other barometer ranges.

Here is the OEM calibration for the intake and exhaust cams at high baro.  During WOT my LH2 operated around .57 g/cyl airmass so I have blue-lighted the .56-.60 areas: [click to zoom in, back to return]

lh2 vvt intake and exhaust cams

What we see is that the intake cam goes from 16-19 degrees at 4400 rpm down to 2 degrees at 6800 rpm.  The exhaust cam goes from 3-6 degrees at 4400 rpm to 4-5 degrees at 6800 rpm.

The values for the intake cam should be degrees of advance, and the values for the exhaust cam degrees of retard.   For the LH2 it appears 0 degrees of either are Top Dead Center (TDC) [ref: Helms manual pg 9-340].   If that is the case, as the engine moves to high RPM the intake cam gets less advanced (retards), and the exhaust cam gets more retard (retards).

camactuatoroperation

Simple cam tuning rules for Naturally Aspirated engines like my LH2: [ref]

  • Advancing both cams => more low-RPM power, less high-RPM power
  • Retarding both cams => more high-RPM power, less low-RPM power
  • Less overlap => more low-RPM power, less high-RPM power
  • More overlap => more high-RPM power, less low-RPM power

So as the engine moves to higher RPM we want to see both cams retarding, and that is what we appear to see.  We would also like to see more overlap, and that is not what we see — the net change between the two cams appears to introduce more overlap not less.

I am interested in the changes over cylinder air mass within the table.  At lower cylinder airmass the changes have the same basic shape, but to different degrees.

LH2 Intake Cam Graph

This graph shows the degrees of intake cam (left axis) vs rpm (bottom axis) at various gram/cyl air pressures.  The top two lines are our lines of interest, which seems odd, but because the graph maxes out at that point every other range over-writes the top line.

I think our first step will be to begin logging the intake and exhaust cam positions in order to verify that there are not other tables having an impact on these values.

What do you see in the data?  How would you tune these values for low-end torque and high end power?

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?