I am wondering if anyone knows why cummins is using an all iron block, instead of something lighter like Aluminum, etc. Its crazy how the 5.9 weighs in close to 1000lbs.

 

Because Iron is strong and has proven reliability over years and years of engine design. Plus, let's not forget the forces involved with this engine. This little ISB runs about 33:1 compression (compare that to a little AL block gasser running 10:1 or so) and the power output is 400+ ft-lbs of torque (these engines survive just fine boosted up to 1000 and more ft-lbs). With that 33:1 compression each cylinder is displacing about 1 liter of air, typically when a gasser gets to the size of these engines there is 8 cylinders to divide that displacement across. and if those engines are putting out 450+ ft-lbs of torque its only in a 50 or so RPM band. These ISBs put out the 400+ ft-lbs over a 1500 rpm range. So, why Iron, because you'd need about as much if not more Aluminum to handle these beasts for the long long haul and with that much Aluminum the engine would probably be twice the size. Another side note on the Aluminum thing, Diesels like having some heat in the head, iron is very good at holding heat in, Aluminum gives that heat away very quickly so for heat efficiency iron is far superior in a diesel.

 

You can get some pretty strong Aluminum(s), but can't disagree with you on the heat retention. I guess its bad enough getting our Diesels to warm up in cold weather with an Iron block, would be worse with Aluminum.

 

I think the compression ratio is about 17.1: 1 and not 33: 1

 

33:1 is the big bore engine like the 855 CID's. They don't need intake heaters with that high of compression

 

33:1 is probly close to right for an ISB at full boost. (Dynamic ratio?). Its mostly calculations and theory. At crank speed, yeah its like 17:1, 12v's were around 17.5

 

aluminum cannot handle high temps like iron. when the engine of the ford or chevy diesel overheats the heads and block actualy warp. it takes alot more heat to distort the iron blocks of our ISB's.

compression is 17:1, dynamic compression when at full boost (28psig which is 2 atmosphere and where the waste gate opens stock) would equal around 52:1 if not a bit more.

at idle you have approx 14.7psia at the intake, at full boost the turbo is able to produce approx 42psia which is 2x higher than normal pressure, however you have to take into account I am starting at a full vacuum.

with that said the air in the cylincers is being compressed by a factor of 17, so with 42psia at the manifold, max pressire before fuel is injected is around 720psia, when the fuel is injected that number go WAY higher

 

Drew, I've seen you say Ford's heads are aluminum a few times, it's not true. Ford still uses cast iron heads. There is a seperate piece on top of the head that is alum, but the business portion of the head is iron.