Why does DDEC 4 have a waste gate

The compression ratio on a diesel is double that(aprox) of a gas engine. Too much boost pressure and you would destroy your compression rings or blow a hole in a piston. Most semi-modern engines limit their boost to around 35 psi(or at least that is where my DDEC 4 was limited to)

 

Two reasons.

One:Streamlining the supply chain. The oem decided to go with one turbo for different horsepower engines.

two: idiot proofing engines. All those just got out of school with no understanding of internal compression mega box New drivers. A normal turbo, like your Borg Warner for example, you need to watch the pyro and boost gauges to keep from getting the engine to hot.

 

My 2000 series 60 has a wastegated turbo and I can tell it opens when I'm limited to ~370 horsepower (exhaust note gets louder & boost stops climbing). When certain conditions are met, the wasetgate will close; exhaust gets quieter, boost rises, and horsepower increases to ~430.

There are folks who say the 370/430 multitorque difference is pedal vs cruise, but I can assure you I'll occasionally get 430 on the pedal (though I haven't been able to predict when or why -- sometimes I'll be on a grade for a while holding a certain rpm when suddenly I'll hear the WG shut and engine surge ahead).


Anyway, my supposition is that the ddec ecm might not be able to support 2 complete horsepower tunes and that it relies on the wastegate to switch between power levels.

 

My DDEC 4 has a waste gated turbo that limits boost to 25 psi. A buddy has an identical truck with a PP non waste gated turbo. I average 7 mpg, he averages 6. He goes up hills faster, I take more vacations with the savings on fuel.
There are many variables and tradeoffs in the engineering of a modern diesel engine in a truck tractor. If you think PP or Rutherford or others can improve what the OEM specifies have at it.
I put my money squarely on Detroit Diesel and Freightliner's engineers.

 

And my dd4 with a Borg Warner gets much better fuel mileage gets much better fuel mileage and power since I took that factory waste gated crap off. Trying to compare your average mpg to your buddies is ludicrous. No two people drive the exact same. You can only accurately compare yourself, to yourself.

 

So many variables there. I would say its pretty much proven that you would do better if you went to the BW 171702. Hell the replacement cost alone is reason to try.

I am averaging 7.3 pulling a 7 car trailer that idles a lot(runs pto) and am pretty happy with that

 

Waste gated DDEC turbo has some advantages. It will spool up a little quicker. But think of a waste gate turbo as a nozzle on a water hose. It is smaller than something like a BW non waste gate turbo, and just like a water hose nozzle, you get a little faster compressor air flow and a little more responsive spool up, which is not a bad thing if one is doing a lot of local P&D kind of work. The whole thing is stupid from a road truck aspect. You don't get the boost that would be better at pulling grades, and you don't get as good of exhaust flow thru it to keep EGT's manageable.

My DDEC IV 12.7 got a BW 171702 with a turbo blanket, and a Bully Dog ported,polished, coated manifold before it was dropped in my glider. The waste gate turbo that came with the motor never saw one minute of time in my truck. I would have it no other way. Great performance and in 449,000 miles on the motor now, it has averaged 7.84 lifetime mpg average. It is a rare day when the EGT's go over 900F on a hot day, pulling a tough grade, with 46K in the box.