Blog Post: E4A2 – Tuned Versus Stock ATS-V LF4

[Bruce Nunnally]

I had been concerned that my test method inherently didn’t capture torque as well. My basic method is sport mode, AC off, use tap-up tap-down on the steering wheel (not the shifter) to select gear 3, then floor it, letting it shift automatically to 4th. From around 45 mph, and by the time it gets cooking we’re at 4000 rpm or so, which is where we see my graphs start. I have been thinking that this suppressed the max torque, because where I should be hitting max torque I was still gathering boost instead. A run from 1000 rpm for example like the GM LF4 engine dyno would let the turbo spool up a lot more by 4000 rpm.

Here is a plot of the GM LF4 engine dyno converted to ‘at the wheels’ versus the current tune.

Tune versus Stock

The blue and red lines are tuned whp and wtorque; the dashed lines are the GM LF4 engine dyno converted to whp and wtorque.

This shows that the torque isn’t “missing” — just as the tune makes more hp, it makes more torque through the ‘range of change’. The tune by nature is focused on WOT benefit, so as to impact daily driving as little as possible. The solid red line is clearly better than the dashed line from 4800 rpm – 6700 rpm. Increasingly so at higher rpm; 43 lb ft better at 5252 rpm, 56 lb ft better at 6000 rpm, 88 lb ft better at 6500 rpm.

It probably is same or better at 1000-5200 rpm as well if there was a more convenient way to test that range off the dyno. Doing the scan from 1000 rpm with an automatic seems impractical.

Torque and HP are inherently mathematically interrelated, so we could not have more of one without more of the other. But this helps me to see where the torque gains are — right out there with the HP where the increased boost is, but also from 4800 rpm on to redline.

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