NVRatio information

[pezfighter99]

Haven't posted before but have read many of the posts with interest. Several of you folks have a fairly good grasp of tuning Hemis so I'd like to "pick your brains".

I'm working with a 2009 Challenger SRT 6 speed with no engine mods except a Whipple supercharger with their cold air intake option and of course, I have the over-active throttle issue. After getting 2 tunes from Whipple, I bought the HPTuner suite and got the throttle response more "reasonable" but a tuner's work is never done, unfortunately.

NVRatio is stated to equal RPM/VSS (VSS being MPH I've read in several posts. Correct me if I'm wrong.) NVRatio is an odd parameter. Using simple algebra, the formula can be rearranged as VSS = RPM/NVRatio. My 6.1L Hemi tune in Power%Request and ExpectedPedal has 9 values for NVRatio ranging from 26 to 1024. If one assumes that the usable RPM range for a 6.1L Hemi is 800 to 6400 RPM, the VSS (MPH) range for each NVRatio can be calculated.

Using the NVRatio extremes, for 1024 the VSS range for 800 to 6400 RPM would be 0.8 to 6.3 MPH. For 26, the 800 to 6400 RPM VSS range would be 30.4 to 246.2 MPH. The MPH range for the remaining 7 NVRatio values would naturally fall somewhere in between the extremes.

It seems that the largest value of NVRatio effects the lowest MPH and the smallest NVRatio effects the highest MPH. I've noticed that in many newer Hemi tunes listed on this forum the largest NVRatios (1000 and 1024) are missing, with 256 being the largest. This, for my listed RPM range, would give a VSS range of 3.1 to 25.1 MPH. Seemingly a more realistic MPH range to control. Controlling any MPH less that 3 would seem ridiculous.

In my case, starting with the largest NVRatio (1024) the MPH range of all progressively smaller NVRatios overlap to some extent. So, what has this got to do with anything, you ask. It somewhat explained what I experienced while driving. While holding the throttle steady, the car would abruptly accelerate faster as the MPH climbed causing me to back off the throttle. I'm assuming the controller passed from one NVRatio-MPH range to the next one on the list.

I might be way out in left field here, but does any of this seem reasonable to you experienced tuners??? Thanks for your attention. (Hope you weren't bored.)

[Hemituna]

If you log NV you will see 1st gear is around 255, 2nd 130ish and so on.
Yes, we use it for throttle response per gear...but you dont want big variations just a gradual increase so the engine feels similiar in each gear.
Use the DD flywheel power table to get the engine response per pedal% vs rpm correct.
It is set for an NA engine so the blower changes things alot.

[spoolboy]

Yes, log NV ratio and see if it cooresponds with what you are feeling.

I would guess you could just zero it out if you'd prefer a "traditional" cable throttle feel.