I have to agree with @BoxTruckDoc and @Timerbell that it's not a great idea!is it safe to ecu tune the hino j08e wd engine to 350hp++ without any other mods?
Totally agree with this! I've got a 2015 Hino 338 with the J08E-WD and tried a mild tune last year, just bumped it to around 310hp for better hill pulls. Even then, I had to upgrade the cooling system and swap the clutch after a few months. The stock setup just isn't built for sustained high power. If you're hauling heavy or running long routes, staged tuning with solid monitoring (EGTs, boost, trans temps) is the way to go.I have to agree with @BoxTruckDoc and @Timerbell that it's not a great idea!
I think you can do it in stages instead and start with a less aggressive tune, maybe 300-320hp, and keep an eye on your EGTs!
If you're running too hot, you'll melt pistons and turbo seals real quick.
You're also going to need to address the clutch, driveshaft, and rear end eventually, as they weren't designed for that kind of power.
So while it might be possible to get the numbers, doing it safely and reliably for the long haul is another story!