bent valves

Here is one of many things I do not understand about the 24V Cummins engine in the Dodge. The cast iron exhaust manifold has a divider plate that separates the front 3 cylinders from the back 3. This divider is the one you have to worry about when you drill for an EGT probe. The stock turbo, HX35, also has this division of exhaust gasses. Why is this division necessary?
I switched from the stock Holset turbo to BD twin turbos. Both of these Schwitzer S300 turbos also had a divided exhaust inlet.
Some people have drilled the turbo division to balance the exhaust flow from all cylinders, but there must be a reason Cummins, Holset, and Schwitzer keep them separated. Inquiring minds want to know.

NoSeeUm

It is for turbine efficientcy.

Consider the firing order. An exhaust pulse comes down one tube from the front of the engine and then one comes down the other tube from the back of the engine. The pulses are alternating in the exhaust manifold tubes and to the turbine.

The manifold is split so that the turbine gets the full brunt of the pulse for a couple of reasons. The space in the manifold is minimized so less energy is wasted by exhaust gases expanding into dead end piping. Also, it minimizes interference between exhaust pulses of present, previous and next cylinders as they exhaust to the manifold.

The turbine casing is split so that it aligns to the exhaust manifold and for the same reasons.

If you look inside a stock manifold the forward and rear tubes have deflectors installed pretty close to the manifold flange. The two in the middle do not. Only guessing, but I would think those deflectors also help out with the process of trying to ensure the turbine gets the maximum exhaust pulse possible.

Jim

bent valves

Tank you NoSeeUm. I never even considered the exhaust pulses, and yes it makes perfect sense. So those people who drill out the separation must be making so much exhaust pressure that the sharp pulse is not needed. I will be able to sleep tonight.

NoSeeUm

LOL

Yeah, I believe that they drill it out thinking that they will get some EGT relief. I have not done it or tested it, but from what I have heard it works for trucks that are pretty much over fueled. I do not know how much EGT relief that they get. I would guess that they are pushing the poor little turbo past any sort of optimum efficientcy.

Jim

Tate

Drilling out the divider will allow the front 3 cylinders to wastegate. The split scroll housing only allows the back 3 to wastegate, so even with it fully open, you will still get boost creep. I can get 40 psi on my turbo regardless of what kind of boost elbow I use. If I drilled out the divider, I'm sure I could bring that number down.