What is the rev limit on a Duramax?

siume99 · July 10, 2002

What is the rev limit on a Duramax? Also, what is red line?

Thanks

SilveradoWV · July 11, 2002

I have a 4.8 and wondered what the red line is, the tach just stops at 6000 so I assume its 6001???????

bluenote · July 11, 2002

The Duramax sorta has 2 red lines. The dotted red area on the tach is where rpm's can go into when grade-braking is engaged. I think it's very difficult to get the rpm's into that area under other conditions (hard acceleration, downshifts), and I haven't been able to do it. The small, solid red area at the very top is your true red line. Based on my experience so far, and what I've read, it would take some kind of catastropic failure to get the rpm's that high.

Colorado Kid · July 11, 2002

Governed engine speed at no load is about 3500 RPM, so the only way you can see RPM higer than that is to have the drivetrain supplying power to the engine (for example using a lower gear going down hill). It is permissible to drive the engine to 4700 RPM in these situations, which substantially increases the engine braking effect available. Why the shaded area on the tachometer starts slightly below the governed speed is anyone's guess...you aren't going to hurt it unless you exceed 4700 RPM, which would take a fairly steep hill and heavy load, and a tolerance for some unusual noise levels. I've had mine up around 4500 RPM briefly when towing a 5'er off of Berthoud Pass, which has steep grades and some 15-20 MPH switchbacks thrown in. If you have an Allison you'll never overrev it, no matter what you try. If you have a 6 speed (like me) you'd have to be trying to break it or else deaf and not paying attention to get it above 4700 RPM.