This is hard to tell I think, because BMW under rated the 335i from the factory with its 300hp rating. Only way to determine this would likely be comparing an engine dyno:
no biggie.
was probably figuring it wrong anyway, likely better to just divide whp by the dtl
whp/0.85 (340/.85=400, 340/.82=415 etc...)
It's really not as straight forward as a percentage drive train loss, it's different amounts at different power levels in different gears, and then all the different makes and models of trannys on top of that, I have a 6MT trans which is basically assumed to have 15% DTL but I wasn't using any of that when posting my crank numbers, and yes BMW heavily under ranks their numbers, I was quoting the Dinan numbers for the stage 3 Power package, which I have on my 335is, which comes from the factory substantially lighter and more powerful than a 335i, with the factory overboost function torque goes up to 370 factory and HP is probly right around there as well, altho the rated HP and Torque is 320 and 331...
Dinan, on their website, shows what BMW claims as stock, and what they actually measure, along with the gains their packages generate, and you can see many times BMW is rounding down, to say the least about factory numbers. This is also where I am getting my CHP numbers from. Stage 3 = 398BHP, 429LbFt... And more than any peak numbers the area under the curve is what counts not so much peak numbers...
Again I don't think DTL "%" is a proper way to look at it as it obviously has different power loss in different gears, RPMs, and many other conditions... But I think the general public accepts 18% for a classic single torque converter automatics, and 15% for a manual stick, and possibly some newer DCTs and even newer TC trannys. The number is just a loose average at best