Nistune Forums

Hi folks,

New to the NIStune system. I have tuned a few cars using other systems, piggyback and stand-alone. I have a Twin Turbo Z32 that I am currently tuning. Took it out on the streets to get the A/F ratios in the right ball park before we take it to the dyno. Low gear pulls are great, high gear high rpm/load is great as well. Problem I am having is getting the A/F proper in 4th gear when loaded up at a lower rpm.

On every image file I've seen the gear map is identical to the primary fuel map, however I had to add an extreme amount of fuel (as compared to the primary fuel map) to the gear map to get anywhere near a safe A/F. The High Gear coefficient is at 47 / 100%

I have read in a different thread that I can set this to 0% to disable the map switching to high gear, and will do so if necessary, but was just wondering what could be causing such a discrepancy.

Is it an AT or MT ? and does it have a non standard twinturbo diff by any chance ?

Transmission type and final drive ratio are essential variables for calculating/choosing the gear-coefficient.

I have found that if the switching to the high gear map occurs too late (because of an incorrect gear-coefficent) it will cause a lean peak in AF ratio during the switch...although it is only for a short moment.

Maybe this is what is happening in your case also...

-Eric

Ok, so the coefficient does not trim the table at all, just decides when the map switch takes place?
Car is a MT with factory diff so, not sure why I would have to change the coefficient, but I'm going to have another go at it today.

the coefficent only determines at what point the switch to the high gear maps takes place, it's not used for trimming or anything like that..

for a MT twinturbo with stock diff and coefficient at #2F (decimal: 47), the high gear map is accessed as soon as 4th gear is engaged.

for the AT twinturbo with stock diff the same applies when the coefficient is set to #1E (decimal: 30): high gear maps are also accessed as soon as the transmission switches to 4th gear (with overdrive switched on)

Not sure why the standard coefficent value doesn't work correctly for this car...maybe it has a non standard diff ? or a non turbo diff, which is a also a popular modification...

Maybe there's something wrong with the speed signal to the ECU or maybe the car has non standard sized wheels ?
In theory running larger (rear) wheels/tires should throw the high gear map switching point off balance, but I have never looked into how much of an effect it has.

RandomHero wrote:Ok, so the coefficient does not trim the table at all, just decides when the map switch takes place?
Car is a MT with factory diff so, not sure why I would have to change the coefficient, but I'm going to have another go at it today.

Eric wrote:the coefficent only determines at what point the switch to the high gear maps takes place, it's not used for trimming or anything like that..

for a MT twinturbo with stock diff and coefficient at #2F (decimal: 47), the high gear map is accessed as soon as 4th gear is engaged.

I thought the gear maps were for 5th and not 4th?

In those cases were nissan enabled the high gear maps, they are used in 4th + 5th gear (MT) or 4th (AT)

but for some reason Nissan decided in 99% of all cases not to use the high gear maps at all..

If you modify the high gear coefficient you can make it use the high gear maps in 5th gear only or eg. for gears 3+4+5.