Cadillac Northstar LH2 4.6L V8 VVT Tuning #hptuners #Motorama

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).


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?

Tuning the Cadillac XLR – MBT #Motorama @hptuners

Torque and horsepower are related, and if we increase torque everywhere across the RPM band, horsepower will go up as well.   What we want to know is what timing or advance will give us the most power?  But also, knowing that more timing can mean more heat and more detonation, what is the minimum timing for the maximum torque from the engine (MBT)?

I recently purchased a 2007 Cadillac XLR with the 4.6L LH2 V8 DOHC VVT engine. I will be tuning this platform and publishing my experiences.


GM helpfully includes a reference table used by the PCM which shows the Max Torque Timing vs RPM vs Cyl Air based on their experiments with the engine design.  This table is shown above for the XLR from the factory calibration file for my 2007 XLR 4.6L.

I highlighted the two rows 0.56 and 0.64 cylinder airmass because at WOT the engine flows from 0.61 to 0.58 cyl airmass.  So those are the rows of interest.  If we get the timing to the values shown along those rows at various RPM values (without detonation), we will maximize the output of the engine.

XLR compare XLR tune to MBT

For this sample I captured the actual advance from the engine, the actual measured cylinder airmass, and then calculated the ideal advance from the MBT table to compare to the actual advance from the engine result.  What we see is that with the heat and other factors the engine is 3 degrees retarded from MBT.  In this range for this engine I believe that is a 15 hp difference.

Now, since some of the gap is CAUSED by intake air temperature (IAT) retard, and some is caused by engine coolant temperature (ECT) retard, we may not be able to get to MBT in the summer heat here in Texas.  But during tuning that is the spark advance I will be shooting for.

Separately, I will be looking at the fueling the engine prefers, the transmission tuning, and transitions.  If you have other ideas or recommendations please reply below.  There is not a lot published on the RWD LH2 Northstar V8, so if you have experience with what worked for you please share.


2014 Cadillac XTS VSport Platinum Day 2

Saturday with the XTS was a breeze of course — the Cadillac is perfectly competent with plentiful, smooth power delivery and grace.  Crest Cadillac is my host for the weekend test drive; read about the pickup here.

Click on any of the photos in the gallery to zoom in, and to flip through the gallery.


It is hard to photo well, but the tail light actually extends enough behind the rear to clearly form a tail fin reminiscent of the iconic 60s Cadillacs.


This photo captures the entry to the driver’s seat illumination at night in the Platinum version, which is Cadillac terminology for over-the-top luxury models.


I think these are the best rear-view mirrors I have seen on recent cars — they are perfectly shaped and sized and provide a huge view ports.  This has been a pet peeve of mine on some recent models who favor small horizontal rectangles for mirrors at the cost of being able to see clearly.   These work very well.


The Platinum has the full driver assist options, including augmented reality backup camera, front and rear proximity warning systems, automatic headlight dim control, lane change warning, and multiple-color, adjustable, customizable heads-up display.

What would I change about the XTS?

  • More advertising — Cadillac is doing a poor job of getting more info out about the XTS, and especially the new AWD XTS VSport and Platinum VSport Models.
  • The rear windows have roll-up shades, which makes the car cooler inside.  It also makes the windows a bit difficult to see through at night or in the evening.

What is my favorite feature?

  • The power plant: Twin-Turbo 3.6L DOHC VVT DI V6 with 410 hp with AWD

Tomorrow will start with an early breakfast run, then Church.  Stay Tuned for more real world impressions.