i wanna learn how to madify a cummins and other diesels

Demon Speed, what size engines are you talking about? Sounds like the larger medium/heavy duty engines?

There are a few different "Gens" for the dodge diesel:
The "First Gens" are from 89-93, they were the boxier truck and didn't come with intercoolers till 91. These trucks have a mechanical injection pump called the VE pump. These trucks can be tweaked with for "free" HP but these are smaller pumps and on fuel only will max out around 330-375HP depending on how well they are set up. These truck make great torque number anywhere from 650-900ftlbs. I've seen one truck up to 500hp but at that much power the truck becomes unreliable, his engine would "run away", rev up all on its own. These are 12v motors and for a while the aftermarket injector selection was meager, now most of the injector companies can make you a custom set rated at just about any HP you want.

2ng Gen trucks came out in 94 and the body style went to 02, but received some updates in 98. 94 to 98.5 trucks came with 12v P7100 mechanical pump. 98.5-02 came with the VP44 pump which was their first electronically controlled pump.
The P7100 pump (P-pump) can make some serious power and still be very reliable. There were a couple version of it 160,180, and 215hp pumps. The 215 pump are more sot after cause they have some bigger/better internals and can support more HP... easily 700-800hp. There are aftermarket pumps called 13mm and 14mm p-pumps and that refers to the pump plungers. These pump can spin the motors up 5-6k rpms and make up to 1500-1800hp.
These pumps have fuel screw, springs, and "plates" that you can change out, modify and do all kinds of things to make power. But yes these aren't "on the fly adjustable".

The 24v Vp44 truck were from 98.5-02. The vp44 has a bad rep for failing all the time... But in reality it wasn't all its fault. The vp44 is lubricated with diesel fuel instead of motor oil like the Ppump and VE pumps. The 24v trucks came with a really crappy electric lift pump that supplies the VP with fuel. These lift pumps would go out anywhere from 10k-100k miles on stock vehicles and in no way could keep up with mildly modified engine. Electric fuel pumps are meant to push fuel instead of pull fuel as well, these lift pumps were mounted on the side of the engine straining to pull the fuel up to the VP. Most people buy after market fuel pumps and install it on the frame back by the fuel tank eliminating the stock lift pump all together. The VP is a smaller pump and maxs' out in HP much sooner then ppumps. On fuel only they are just getting to 700-850 or so hp with aftermarket VP pumps. They are just breaking the 1060hp mark with nitrous.

Now all of these motor use a "mechanical" type of injector. It uses shims to adjust "pop off" pressure, when the injector injects.

In 03 and newer trucks they went to a Common Rail injections system. This system's injection pump is called a CP3 and all it really does is create pressure. The injectors have an electric solenoid and can be controlled a lot more then the previous injectors.... There is all kinds of crap on these truck and I dont know too much about them so I'm not going to get into these.


But some other things to think about is most automatics SUCK when they are stock behind a Cummins. It seems like they basically took a small V8 trany and stuck it back there. The design of the trany its self is great! But the stock valving and pressure are too weak. An aftermarket auto is one of the best upgrades I've done and really changes the characteristics of the truck.

There are a lot of things you can do to these trucks. Its crazy how much HP you can get of these and still get great fuel mileage and drive it everyday. Cummins has a 1/3 less rotating parts then a powerstroke or duramax. Working on a cummins is very easy. But watch out... it gets addicting and your other projects might get neglected.