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?

Monitoring IAT, IAT2 Cadillac STS-V

This morning I did some data-logging with HPTuners up and down the highway.  I am still learning the software, so feel free to make suggestions.

I grabbed these screen shots of a couple of points: (click on the image for a zoom-in version, then hit back to come back):

HPTuners datalog screenshot 1

What the first screenshot shows is that at 69 mph and 6651 RPM the supercharger was making 10.7 psi.  During this portion of the run, ambient air temperature was 90F, IAT air coming into the MAF temperature sensor was 108F, and IAT2 air leaving the intercooler was at 151F.

Actually I would have expected the car to shift at 6500 rpm, but 6651 is close enough I suppose.

In the chart display at the bottom however, you can see that the IAT2 was already elevated before the higher-RPM event occurs.

The question for today though is how the IAT2 151F compares with ambient air 90F.  The Supercharger adds heat to the intake air in the process of compressing it.  At maximum RPM as here, the Supercharger is spinning at 2.1:1 and so 13,967 rpm.   This can add up to 200F to the air coming into the intercooler.   Today the air coming in to the supercharger was already 108F, so heating it by a couple hundred degrees puts some very hot air across the Laminova intercooler tubes. The goal for the Intercooler is to reduce the heated air back as close to ambient air as possible, pulling the air back from 200F+ down to 151F in this example.  The unachievable ideal is that the intercooler get the air down to the intercooler heat exchanger’s own cooling source, which is the ambient air coming into the front grill at 90F.

HP Tuners datalog screen shot 2

In the second screen shot, at 39 mph and 6502 rpm, ambient air was 88F, MAF intake air 108F, and IAT2 after the supercharger was 135F.

On a separate topic, long term fuel trims appear to be small, which I think is good.

Points to ponder:

How to reduce the IAT2 temperatures from 151F when accelerating at highway speeds

Why the max pressure seen was 10.7 psi instead of 12 psi?  Is this also temperature related?

How will these readings change in cool air?