It’s real humorous when someone says a performance cam doesn’t make power in a diesel. It’s the same as saying a billet set of connecting rods doesn’t make power.
Truth is both statements are true.
Cam and rods don’t in and of themselves make power. What a cams does do, is allow you to make power by allowing the window in to the combustion chamber that air flows, open wider, and longer.
first To establish my credential’s I have been designing high performance cams for 25 years, and cams for diesels for the last 10 year. I have sold over 4000 cams for Cummins and Duramax engines. Diesels can’t get enough airflow, no matter how good the head, or cam, so any improvement in the cam is good.
The next silly deal is when a person says that a stock cam is good enough. Any OEM builds a cam for the least amount of trouble. Short, easy on the ramps and little lift beyond what’s minimally needed to make rated power.
I have many hours of time on the engine dyno helping to develop power in many different programs. This includes diesels. I know what a diesel likes and on a street engine more is better within reason. Lift is not important if you don’t have a head that works “flows “up at a higher lift. Leaving the intake open 10 more degrees is dramatic on volumetric efficiently. this is evedent on the CFM numbers from the air hat
When designing a cams program, I don’t look at overlap, intake center line, or lobe separation angles. Those terms are nothing but yardsticks for layman to compare cam profiles.
There are 4 events on a cam that matter , open of the exhaust , close of the exhaust , open of the intake and close of the intake.
Rule 1 Diesels do not like both valves open at the same time period. OEM does this for passive EGR.
Rule 2 the exhaust valve must close at around, or shortly after TDC. Set this in stone.
Rule 3 the intake valve should open when the exhaust is fully closed. See rule one if you don’t agree
Rule 4 the closing of the intake valve is open for discussion. The poorer the intake ports, the longer you can leave it open. The higher the intended rpm, the longer you can leave it open.
So in summary, if you put a cam in and do not change any other parameters. You will get little, if nothing in return on a dyno. What little you see is the engines ability to pump air more efficiently and get up on the power curve quicker. What you will get is a reduction in EGT’s and spool time. With that reduction in EGT’s you can now put more fuel in it and here is where the power comes from.
This isn’t magic, it’s a just math.