SP Engineering has tuned some of the most powerful Nissan GT-R’s so far. They have at least three R35’s that are pushing over 700 horsepower to the wheels. They have run into a problem, that has been talked about, but not too much in the open as of yet. Something a lot of the tuners have been working on. At first the high power cars were being tuned with the Haltech, and not able to shift from 3rd to 4th gear under full throttle. SP Engineering’s demo car, and a customer car both ran into the same problem with the Greddy turbo kit, and the Haltech.
GTR was also making over 750 in torque with the very same kit. Both vehicles were tuned with the Haltech unit. From what we've encountered was this mysterious "NO SHIFT" issue from 3rd to 4th gear. We've been working with Haltech to resolve this issue on a daily basis. We feel the TCM is definitely the reason behind this shifting issue once you reach high torque numbers.
SP Engineering then has been developing their own turbo upgrade kit – the SPE750. The SPE750 kit is being tuned with the Haltech and has also been tuned with the Cobb Accessport .
Stage 1 SPE750 package and Wayne's R35 was next in line. Haltech was also used which produced torque numbers of 782 and encountered this "NO SHIFT" issue as well. Keep in mind the more power and torque we've made on race map this occurs on every setup we've tried. Running the power levels on pump gas levels did not have any issues at all.
91 pump gas was first in line and achieved power gains of 680 awhp and 676 Torque. 109 race fuel was next in line and achieved power gains of 720 awhp and 709 torque. From what we've learned, this "NO SHIFT" issue will ALSO occur using the COBB AP once you've reach high torque numbers shifting between 2nd and 3rd gear.
SP Engineering say they are working with Cobb and with Haltech on a solution to this problem. Until this solution gets worked out, the TCM will be holding up further development, and possibly a 9 second quarter mile pass.
The TCM for the GR6 Transmission is something new to most tuners, however it is something that will need to be looked at in the future, as most performance cars will be dual clutch, and extracting maximum performance will require both engine, and transmission tuning.
Source: NAGTROC forums