Highest RPMs should go?

You risk blowing the turbo charger. Should stay below 2000.

 

What engine, makes all the difference.

 

Depends on the engine. Should say on the valve cover max rpm..
Mines only an 1800rpm max, 1925NL.
If the Jake's won't hold her back by 1925, I press the service brake & bring her down 7-9mph & repeat till I'm safely off the grade..

 

Accidently ? How does that happen ? Must be an automatic or u would know u was in to low of a gear

 

Yeah I wouldn't do that again.

 

Typically on a large, 12-15L diesel you don't really want to get above 2,100 to 2,200 RPM.

Did 2,700 hurt it? Probably not. Issue with overspeeding is you start to see "valve float" at high speeds. The valve springs can't get the valve closed in time. You risk major valve train damage and a piston can smack a valve.

Then you add in the inertia of the pistons going from dead stop to full speed extremely rapidly. Very easy to throw a rod.

You've got the flywheel and clutch housing to worry about as well.

 

If any of you are interested in seeing the carnage on the valvetrain from an overspeed, check out this recent thread:
Click Click Boom!!!!!

 

Not even. There are ways to force a DT12 into a gear that much lower than you should be in, but they're all quite intentional... and also not worth the effort to pull them off, either. Better off stabbing the brakes and praying IMHO