Can DPF back exhaust help?
Hell yes!
Why and how? Glad you asked…..
Steve at Banks Power mentioned a wonderful drinking straw analogy and I love it. Imagine blowing through a 12 inch straw not hard right? Now what if the straw was 10 feet, or 120 inches long? Oh wow. You could hardly blow through it. What you are feeling is back pressure, because all matter has mass, so does air! The air in the straw has mass! If you take that straw, lets say about .25 inch in diameter and connect it to a larger diameter straw half way down, you decrease back pressure, why???
The rapid expansion of air as it exits the small straw into the larger one results in decrease back pressure. Its similar to the smaller straw just being shorter. Why no DPF dump? It would be a fire hazard (hot regen) and it would be stinky in general, who wants that ammonia smell under the cab? Not safe, as clean as new diesels are , we still have to take the exhaust out the back.
Ford and Ram use about a 3.75 inch exit on the DPF, flanged on the fords and a slip fit connection on the Rams. When we swedge this up to 5 inches there is a significant drop in pressure vs the 3.5 factory over the axle pipe. On the Ford its even more gains due to the loss of the power robbing venturi at the tips and near the last bend (air mixing inlet) .
At 50+ MPH, the slash cut large oblong tip also creates a venturi effect decreasing backpressure further.
And best part is, that venturi is not needed. GM and Ford small exit systems used that to cool hot regen exhaust and now, with the 5 inch pipe, the rapid expansion from about 3.5 inches results in cooler, safe tips at the exhaust tip!
Since installing this system on one of our shop trucks, we have seen EGT 1 sensor temperatures 50 degrees cooler in the same conditions (80 mph cruising unloaded). Lower EGT near the turbo is great for the turbos life expectancy as the oil will degrade less over time.
In addition the truck is more responsive and looks better. Really hard to beat the improvement you get for 30 to 45 mins of work! On the Fords, about 11 hp is the average gained on the Dyno and that number is about 10 for the Ram and 17 on the Duramax trucks.