The greater the HP you are trying to achieve the lower the RPM the engine will go flat at, simply because time to put enough fuel in the barrel is lessened.Īs you increase fuel galley pressure from higher PSI lift pumps so that you can try to fill the barrel quicker while it is uncovered as soon as the plunger raises enough the cover the fill port the pressure exerted through the fill hole against the plunger will push it to one side and it will start to score. At some point there is not enough fuel to make enough HP to keep accelerating, the engine goes flat. As we have less time, less fuel will get into the barrel the less fuel in the barrel the less HP the engine can produce. It takes X seconds for fuel to go through the fill port and fill the barrel, as the engine goes faster the time available that the port if uncovered for fuel to go in gets less than X, the faster it spins the less time (–)X we have. We all know those engines don’t last, they can’t make power more than a few seconds at a time and if you add up all the seconds in-between rebuilds it would not even 1 lap around the course in Key West! It has nothing to do with governors, springs or anything other than fluid dynamics, you can take the governor off and control the rack by hand if you want to and the engine under load will still not go 1 rpm faster and here’s why but there is one way around it somewhat – if you had bigger enough plungers and barrels that when starved still can flow enough fuel to make the HP you want to go the rpm you want, the engine could turn faster BUT the you would over fuel at low and midrange RPM’s sooo much it would look like those tractor pull engines with all the BLACK SMOKE pouring out. I have said before the rpm is limited by the time it takes for fuel to fill the barrel on a P style pump. The 8.3 are so long and heavy you need a big engine bay to carry them in, are far as how fast they will spin stock not much over 3,500 rpm without problems, the pistons and pins, rocker arms, push rods weight too much and you’ll stretch the rods, bang valves or heads and go boom! There are bigger plungers and barrels for that pump to make all kinds of HP but that opens up other problems (see below)
#8.3 cummins torque specs mods
With a Nippendso pump off an old style 300B the 8.3 can make 450-500hp with the addition of a higher pressure lift pump and no mods other than turbo and bigger after-cooler. 8.3's right from Cummins are 600hp marine the early mechanical engines were up to 450hp direct from Cummins.
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