4BT Exhaust Minimum Diameter

[Smitro]

I have twin Cummins 4BT’s (150hp) with the standard OEM exhaust elbows bolted directly to the turbo outlet flange. I plan to fabricate my own dry risers to increase the spill over height. The existing ID of the factory elbow is 58mm at the smallest part. The new dry riser will have 3 long radius bends and approx  length of 500 – 700mm to where the wet mixer where the Dia will increases to 100NB.  Will using 65NB pipe for the dry riser on the engine side of the wet mixer cause restriction and hamper engine performance?

Topic

[Tony Athens]

All is good..

[Smitro]

Hi Tony / Francis,

I should have elaborated a little. The 65nb that I mentioned for the dry side is 316ss sched 10 pipe (2 1/2″) and wet side will be 100nb 316ss sched 10 pipe (4″) 

I will keep the length on the wet side as short as possible to still achieve the higher spill over height. Just didn’t want to create any restriction.

Thanks for the confirmation 🙂

[Tony Athens]

10 Ga 3″ tube ( expensive) or 2.5″ SCH 10 SS pipe using Long Radius 90’s ( cheap and east to get) is good for the dry side..

3″ pipe size  / 3.5″ OD sch 10 for the wet side.

 

 

[Francis Valerio]

I would say that 3″ is good to go as a “minimum” for the dry part of the exhaust.  The mixing elbow probably would be good to increase to minimum of 3-1/2″ to the rear outlet.

With pushing water thru the “wet” part you theoretically decrease the airflow and making it 3 1/2″ should compensate.  You can not hurt yourself going bigger either, like say 4″…

Tony and his moderators are experts here and will correct me if I am wrong

 

Good luck

 

FV

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