Engineers spent many hours & iterations to optimize the tune in your Cadillac.  But once you make some changes to the configuration and performance of the Cadillac, where is the best tune now?

I continue to enjoy Cartest2000 as an analysis tool.  This what-if analysis shows a comparison between a modified STS-V with 500 hp using a 6400 rpm redline (shiftpoints, which since the program assumes the automatic shifts at redline become the effective redline) and one shifting at 6800 rpm.  The LC3 engine in the STS-V has an actual redline at 6800 rpm, so we are well within the design operating range of the engine.  Waiting to shift at 6800 rpm gives a 0.11 advantage in 0-60 time, and a 0.15 advantage in the quartermile.

This table shows the shift logic for the 6L80 used in the STS-V.  The transmission starts to shift from 1->2 at 30 mph, 2->3 at 58 mph, and 3->4 at 94 mph.  When it actually shifts is around 0.3 seconds after this point.  If the vehicle is at maximum acceleration from a standing start that may hit at redline; at slower acceleration on the highway that may hit below redline.

This graph is a parameter sensitivity analysis — used to show if one varies the shift point, what the result is in order to study how sensitive that result is to this parameter.  In this case, we see the ideal effective redline or shift point for the quartermile would be around 7100 rpm.

Hp Tuners Gauge View

This graphic shows a gauge view from a HP Tuners scan at the moment the car opted to shift from 2 to 3 under wide open throttle acceleration — at 58 mph as expected.  Although at wide open throttle, during this shift the engine reached a max of 6,087 RPM — not near the 6400 RPM or 6800 RPM.

The shift completed around 0.4 sec later at 67 mph.  Note: click on images to see them larger; hit back to return to article.

My conclusion is that a slightly higher speed & RPM for wide open throttle shifting in sport mode would be within design parameters, and beneficial for performance.