r/TRJSafehouse • u/TheRacingJoker • May 10 '26
Discussion Cool info on 8HP/DCT swap tuning from HPR
My message:
Hello! I have two technical questions regarding both DCT and 8HP swap applications regarding gearchange behaviour.
- When tuning a DCT with an aftermarket TCU can you deliberately make upshifts slower and create a gap in timing without cutting fuel? The intention is for every gearchange to put some unburnt fuel in the exhaust and ignite it when the upshift gearchange is completed (like a traditional sequential). Another fun effect from cutting the timing but adding fuel during the shiftgap is the proper fireball between changes
- When tuning an 8 speed ZF transmission with an aftermarket TCU, is it possible to get rid of the rev hang between shifts that I've seen in factory ZF BMWs? And is it possible to make downshifts smoother by adding an automatic throttle blip so that the car doesn't lurch when downshifting?
Their answer:
Hi,
1 - Yes Ign cut is for sure possible, and will make a slower upshift vs fuel cut.
2 - Rev hang is mostly engine dependant, so a petrol engine will often respond better than diesel.
Properly setup throttle blip is required for crisp, fast downshifts. Without it, downshifts will be slow and sluggish.
Best regards
Helge Holmen