2021 Ram 3500 H.O.

4x4ord wrote:
^^^^And he said he’s already installed a dual disc clutch ..... so I’m kind of curious what steps would a person need to take to build a reliable, deleted, non smoking, tow unit? Say to get the truck to a USEABLE 400 RWHP. Cummins increases boost and lowers the compression ratio to add power.... Are those mods unnecessary if only adding 120 HP? (But again wanting to be able to use the power while towing) Is a new air to air and radiator necessary? I guess if all you have to do is swap out the exhaust and add a tuner it’s not terrible expensive.

400 rwhp is already usable on the Cummins. In fact, that is exactly the power level that most tuners call their "heavy tow tune" on the Cummins. I know my hot shot buddies generally leave theirs on 425 hp, but they have aftermarket turbos. The exhaust side of the HE351 VG turbo on the Cummins is your bottleneck. It is small and very restrictive so you would have a hard time sustaining higher power levels while keeping EGT's in check.

It is not about adding boost to increase power. It is also about injection timing, injection duration, and injection pressure. Just as it does on a gas engine, increasing these will increase power, but will also increase emissions specifically NOx and PM. Boost is just an after thought on a diesel. Remember, a diesel is regulated by fuel, not air, so the amount of air it is using is determined by how much fuel is injected. It is the opposite for gas engines where the amount of fuel being injected is determined by how much boost(air).

As stated before, the Cummins HE351 exhaust housing is small and restrictive. This is good at quick spool up and keeping power even at higher altitudes, but it is not good if your goal is to achieve the highest power levels possible. It is not just about boost either. Flow also has a lot to do with it. At 15 psi, my turbo is flowing a lot more air than the HE351 turbo is at the same psi. If I recall correctly, the HE351 has a flow of around 60 lbs/min while my turbo is 82 lb/min.

Also, Cummins did not lower compression ratio to increase power so to speak. They lowered it to meet NOx emission while increasing power. They could have kept the same compression ratio and easily increased power, but NOx levels would have been high. So in order to increase power and to keep NOx within regulations, they had to lower compression ratio which in turn also lowers the efficiency of an engine. Hence the reason why the lower output "efficiency" Cummins with 68rfe has a much higher compression ratio of 19:1 versus the high output engine.

You will notice this with all of the big three diesels. As power output increases, compression ratio decreases. The Duramax used to have a compression ratio as high as 17.5:1, but overtime as they increased power, it decreased to 16:1 with the 445 hp L5P. The 6.7L Powerstroke used to be 16.2:1 and now it is 15.8:1 with the added power of the 475 hp 2020 PSD. The 6.7L Cummins used to be 17.3:1 and now it split to 16.2:1 for the 400 hp high output and 19:1 for the 370 hp standard output or "efficiency" engine. Notice one big thing about these compression ratios compared to the HP outputs of each engine?

So those who say that they wish the engine makes would focus on efficiency rather than power do have a point. The more power they add, the less max efficiency potential the engine has due to lowering the compression ratio in order to stay NOx compliant at that power level. This loss in engine efficiency can be made up in other ways like gearing and so on, however, you are still losing max potential efficiency by wanting more power on a stock truck that has to be emissions compliant.