This maybe a dumb question but could someone please explain drive pressure and back pressure to me? I read all the time about how bad high drive pressure can be on these trucks. I just want to make sure I'm within safe limits.

 

Very simply, drive pressure is the pressure that is "driving" the turbine wheel in the turbocharger. This is also the same as the backpressure that is seen by the engine.

A drive pressure gauge would usually be connected to the exhaust manifold. What is too high? Well, that kindof depends on the efficiency map of the turbo. Generally speaking, it's not desirable to have much higher than a 1:1 ratio of drive pressure to boost. In other words, you don't want drive pressure to be much higher than boost pressure.

However, if you push a turbo out of it's efficiency range, drive pressure can begin to skyrocket. For example, the stock turbo may be able to make 45 - 50 pounds of boost with enough overfueling, but the drive pressure needed to do so would likely be above 60. This is where it gets into the dangerous zone for headgaskets, piston/valve interference, etc.

I think the highest recommended induced back pressure is around 60 - 62 psi for these engines (and that is close to the back pressure that most exhaust brakes provide to the engine as stopping power).

Some people say that they can detect when the 3rd injection event is firing on our engines due to a few psi difference in the drive pressure.

If you use a boost gauge to read drive pressure, it's probably a good idea to install a scrubber, or gas particulate filter inline as well.

--Eric

 

Running around on level 5 on the juice with a stoke turbo a bad thing?